PNITEBSITY OF CALIFORNIA PUBLICATION 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 THE EVAPORATION OF 
 GRAPES 
 
 BY 
 
 W. V. CRUESS, A. W. CHRISTIE 
 
 AND 
 
 F. C. H. FLOSSFEDER 
 
 BULLETIN No. 322 
 
 June, 1920 
 
 UNIVERSITY OF CALIFORNIA PRESS 
 
 BERKELEY 
 
 1920 
 
David P. Barrows, President of the University. 
 
 EXPERIMENT STATION STAFF 
 
 HEADS OF DIVISIONS 
 
 Thomas Forsyth Hunt, Dean. 
 
 Edward J. Wickson, Horticulture (Emeritus). 
 
 Walter Mulford, Forestry, Director of Resident Instruction. 
 
 Herbert J. Webber, Director Agricultural Experiment Station. 
 
 B. H. Crocheron, Director of Agricultural Extension. 
 Hubert E. Van Norman, Vice-Director; Dairy Management. 
 
 James T. Barrett, Acting Director of Citrus Experiment Station; Plant Pathology 
 William A. Setchell, Botany 
 Myer E. Jaffa Nutrition. 
 Charles W. Woodworth, Entomology. 
 Ralph E. Smith, Plant Pathology. 
 J. Eliot Coit, Citriculture. 
 John W. Gilmore, Agronomy. 
 Charles F. Shaw, Soil Technology. 
 John W. Gregg, Landscape Gardening and Floriculture. 
 Frederic T. Bioletti, Viticulture and Fruit Products. 
 Warren T. Clarke, Agricultural Extension. 
 John S. Burd, Agricultural Chemistry. 
 Charles B. Lipman, Soil Chemistry and Bacteriology 
 Clarence M. Haring, Veterinary Science. 
 Ernest B. Babcock, Genetics. 
 Gordon H. True, Animal Husbandry. 
 Fritz W. Woll, Animal Nutrition. 
 W. P. Kelley, Agricultural Chemistry. 
 H. J. Quayle, Entomology. 
 Elwood Mead, Rural Institutions. 
 H. S. Reed, Plant Physiology. 
 L. D. Batchelor, Orchard Management. 
 J. C. Whitten, Pomology, 
 t Frank Adams, Irrigation Investigations. 
 
 C. L. Roadhouse, Dairy Industry. 
 R. L. Adams, Farm Management. 
 
 F. L. Griffin, Agricultural Education. 
 John E. Dougherty, Poultry Husbandry. 
 L. J. Fletcher, Agricultural Engineering. 
 Edwin C. Voorhies, Assistant to the Dean. 
 
 fin co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture 
 
THE EVAPORATION OF GRAPES 
 
 BY 
 W. V. CRUESS, A. W. CHRISTIE, and F. C. FLOSSFEDER 
 
 CONTENTS 
 
 PAGE 
 
 I. Purpose of Investigation 421 
 
 II. Acknowledgments '. 422 
 
 III. Principles of Evaporation 423 
 
 (a) Necessity of Heat 423 
 
 (6) Modes of Conveying Heat 424 
 
 (c) Necessity of Air Circulation 424 
 
 (d) Humidity Control 425 
 
 (e) Miscellaneous Requirements 427 
 
 IV. The University Farm Evaporator 428 
 
 (a) List of Materials and Cost of Construction 428 
 
 (6) Description of the Evaporator Used in 1919 430 
 
 (c) Course followed by Grapes at Evaporator 434 
 
 id) Suggested Revisions in Plan of University Farm Evaporator 436 
 
 V. Cost of Operation 441 
 
 VI. Results of Investigations 442 
 
 (a) Dipping 442 
 
 (6) Sun Drying vs. Evaporation 447 
 
 (c) Sulfuring 450 
 
 id) Effect of Temperature on Quality and Rate of Drying 451 
 
 (e) Effect of Construction of Trays 452 
 
 (/) Comparison of Gravity and Air Blast Burner 455 
 
 ig) Comparison of Disc and Multivane Fans 456 
 
 ih) Exhaust vs. Positive Blower Fan 458 
 
 ii) Recirculation of Air 459 
 
 ij) Direct Use of Gases of Combustion in Drying 461 
 
 ik) Moisture Content of Evaporated Grapes 463 
 
 (Z) The Determination of Humidity 465 
 
 (m) Measurement of Air Velocity 467 
 
 in) Experiments on Stemming, Seeding, and Packing 467 
 
 VII. Summary 469 
 
 I. PURPOSE OF THE INVESTIGATION 
 
 Drying has proved to be one of the most feasible methods of 
 converting the wine grapes of California into a non-perishable salable 
 product. In the hot interior valleys, where the grapes ripen early, 
 the fruit may be dried successfully on field trays in the vineyard. 
 
422 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 However, at least 50 per cent of the wine grapes are grown in regions 
 where the grapes ripen so late that sun-drying can not be safely 
 undertaken, because of the danger of loss through early fall rains. 
 
 In the raisin-growing districts, serious loss from early rains to Sul- 
 tanina and Muscat grapes on drying trays has occurred several times 
 during the past ten years. Some provision should also be made for 
 utilizing the second-crop Muscat grapes which in former years have 
 been sold to wineries and distilleries. These grapes ripen too late in 
 the fall to permit of drying them in the sun. In the aggregate, they 
 amount to many thousand tons, and formerly were a source of con- 
 siderable revenue to the raisin growers. 
 
 The cull Tokay and other cull table grapes from the packing houses 
 and the inferior bunches left on the vines have been used principally 
 for wine making in past years. Much of the brandy used in the 
 manufacture of sweet wine was made from this cull fruit and resulted 
 in a small return to the grower. 
 
 It is contended by many that a greater yield and a better quality 
 of raisins are obtained by artificial drying in an evaporator than in 
 the sun. 
 
 Because of these important reasons it is imperative that there be 
 available for producers of all varieties of grapes reliable information 
 on the construction and operation of evaporators for the drying of 
 raisin grapes, wine grapes, cull table grapes, and second-crop Muscats. 
 The investigations recorded in this publication were carried out for 
 the purpose of obtaining such information. While the magnitude of 
 the problem has made its completion in the one season's time devoted 
 to it impossible, we believe the results obtained to date are sufficiently 
 important and conclusive to warrant their publication. 
 
 Most of the data reported were obtained in the commercial 
 evaporator at the University Farm, Davis, although a great many 
 small-scale experiments were made in our experimental evaporators 
 at Berkeley. 
 
 II. ACKNOWLEDGMENTS 
 
 The erection of an evaporator of commercial size was made possible 
 by a grant of $2500 from the State Board of Viticultural Commis- 
 sioners with which the equipment and most of the building materials 
 for the evaporator were purchased. 
 
 Through the courtesy of Dr. J. C. Whitten of the Division of 
 Pomology, a portion of the Deciduous Fruits Appropriation passed 
 by the last State Legislature was applied in the employment of a 
 
Bulletin 322 THE EVAPORATION OF GRAPES 423 
 
 chemist who cooperated in carrying out the investigations. "Without 
 these two special funds very little investigational work could have 
 been performed. 
 
 The writers wish to thank Professor F. T. Bioletti for the valu- 
 able suggestions given during the planning and construction of the 
 evaporator and during the investigations. 
 
 III. PRINCIPLES OF EVAPORATION 
 
 The construction of evaporators and the discussion of the experi- 
 mental results will be better understood if the more important prin- 
 ciples and previously existing data on fruit evaporation. Evaporators 
 of many types have been used with varying degrees of success for 
 many years. From the experience gained in the use of these evapor- 
 ators and from observations and measurements taken by scientific 
 investigators certain principles have become recognized. To this exist- 
 ing knowledge new information is being constantly added and some 
 of the older theories are being discarded or seriously modified. 
 
 (a) NECESSITY OF HEAT 
 
 Evaporation of fruits involves the change of water from the liquid 
 to the vapor state. This change requires the expenditure of a very 
 definite amount of heat regardless of the system of evaporation and 
 the temperature used. This quanitity of heat is known as the "latent 
 heat of vaporization" and is equal to the amount of heat given off 
 when steam condenses to water. 
 
 Expressed in the usual heat-unit terms, approximately 965 British 
 Thermal Units of heat are required to evaporate one pound of water. 
 A British Thermal Unit (B. T. U.) is the amount of heat used in 
 raising one pound of water one degree Fahrenheit. To the heat 
 actually used in evaporation must be added that needed to raise the 
 fruit from its original temperature to that of the evaporator. This 
 ordinarily amounts to 50 to 75 B. T. U. per pound of fruit; thus 
 making the total minimum quantity of heat necessary slightly above 
 1000 B. T. U. per pound of water evaporated. 
 
 The fuel efficiency of an evaporator may be judged by its approach 
 to this minimum in its heat requirements. If the drying ratio of the 
 fruit, the weight of fruit evaporated, the quantity of fuel consumed, 
 and the heat value of the fuel are known, the heat efficiency of the 
 evaporator may be calculated. In most evaporators it will be found 
 that not over 50 per cent of the heat generated in the furnace is 
 
424 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 utilized in drying the fruit because of the heat lost by radiation and 
 leaks in the evaporator and the heat lost in the exhaust air. This last 
 loss is the greatest. A typical case will show its magnitude. If the 
 outside air at 80° F. is heated to 160° F., as it enters the evaporator, 
 and if it leaves the evaporator at 120° F., it is readily seen that only 
 40° F. of the 80° F. rise in temperature is utilized, or less than 50 
 per cent of the heat is utilized in drying, if we include radiation and 
 other minor losses of heat. 
 
 Many evaporators have failed because they have not been supplied 
 with sufficient heat. The air heating system must have adequate 
 capacity and should supply an abundance of heat without the need 
 of forcing the furnace. The attempt to force the furnace beyond its 
 capacity has been a very common cause of loss of evaporators by fire. 
 
 (ft) MODES OF CONVEYING HEAT 
 
 Heat may be applied or conveyed to the fruit in several ways. It 
 may be conducted by direct contact of the fruit with the heating 
 system. This method of conveying the heat has not been used in 
 practice to any appreciable extent because the high temperatures of 
 the heating element would scorch the fruit. In European countries 
 community bake ovens are often used for drying fruits after the 
 bread has been removed, the fruit in many cases resting in contact 
 with the hot bricks of the oven. 
 
 Heat may to a limited degree reach the fruit by radiation, just 
 as heat is radiated into a room from a fire place or stove. In the 
 stack and tunnel types of evaporators it is probable that this mode 
 of heat transfer is of appreciable importance but in the average air- 
 blast type of evaporator it is negligible. 
 
 By far the most important method of heat transfer is by air 
 currents, which may, if we use the term rather loosely, be termed 
 ''transfer of heat by convection." The air is heated by contact with 
 a furnace, radiating pipes, or other heating system, and the heated air 
 rises through the drying compartment because it is lighter than the 
 outside air or it is transferred over the fruit to be dried by means 
 of a fan. 
 
 (c) NECESSITY OF AIR CIRCULATION 
 
 Since a large amount of heat is essential for successful drying 
 and since air is the usual vehicle for transfer of this heat from the 
 furnace to the fruit the necessity of air circulation in the evaporator 
 
Bulletin 322 THE EVAPORATION OF GRAPES 425 
 
 can be seen. Just how important this factor is, may be seen from the 
 following consideration. It will require approximately 63,000 cubic 
 feet of air dropping one degree Fahrenheit to furnish 965 B. T. U., 
 the heat necessary to evaporate one pound of water ; or it will require 
 approximately 1575 cubic feet of air dropping 40° F. to furnish this 
 amount of heat. A 40° F. drop in temperature is probably greater 
 than that taking place in the average evaporator; consequently, 1575 
 cubic feet of air per pound of water evaporated may be considered 
 in the nature of the minimum air requirement. An evaporator 
 holding 5 tons of grapes which dry in 24 hours and which have a 
 drying ratio of 3:1 must evaporate 6666 pounds of water per 24 
 hours, or 4.6 pounds per minute. This will require a minimum of 
 4.6X1574 = 7245 cubic feet of air per minute. If the drying 
 period is 12 hours, approximately 14,500 cubic feet of air per minute 
 will be needed. A few evaporators have during the past season dried 
 wine grapes in twelve hours but twenty-four hours time or longer 
 was required in most cases. In our small evaporator at Berkeley 
 which was supplied with an excess of air, grapes were dried in from 
 six to twelve hours, indicating the possibilities of reducing the drying 
 period of grapes by increasing the air supply, which means also 
 increased heat supply. 
 
 (d) HUMIDITY CONTEOL 
 
 Air circulation is also important as a means of carrying away the 
 moisture evaporated from the fruit by the heat. In a "dead air" 
 space, heated fruit for a short time rapidly gives up its moisture to 
 the surrounding air which soon becomes saturated and further 
 evaporation ceases unless the saturated air is replaced by fresh dry 
 air. The moisture-carrying capacity of air is relatively limited ; hence, 
 a large volume of air must pass over the fruit to carry away the 
 moisture if drying is to be continuous and rapid. A rough conception 
 of the amount of air needed for this purpose under average conditions 
 may be had from the following consideration. 
 
 At 101° F., approximately 350 cubic feet of air at the saturation 
 point is required to carry one pound of water. At 128° F., this same 
 volume of air will hold at saturation two pounds of water vapor, 
 and at 155° F., four pounds of water vapor; that is to say, each 27° F. 
 rise in temperature will double the moisture-absorbing power of the 
 air. At 120° F., 350 cubic feet of air will absorb about 1% pounds 
 of water vapor. 
 
426 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 These figures refer to air saturated with moisture vapor; that is, 
 air of 100 per cent relative humidity. Relative humidity may be 
 defined as the percentage of saturation of air with water vapor, 
 although the condition applies also to a space which may be free 
 from air. In most commercial evaporators, however, we are dealing 
 with air. 
 
 Few evaporators raise the relative humidity of the air above 50 
 per cent. If the air leaves the evaporator at 50 per cent relative 
 humidity and at 120° F., it will carry approximately 1% pounds of 
 water vapor per 350 cubic feet or each 1000 cubic feet will carry 
 approximately five pounds of moisture. For an evaporator drying 
 5 tons of grapes per 24 hours, approximately 5 pounds of water must 
 be removed from the grapes per minute, or at least 1000 cubic feet 
 of fresh air must be drawn through the evaporator per minute to 
 carry away the moisture. 
 
 In the above calculations to determine the amount of air necessary 
 to carry the required amount of heat to the fruit it was found that 
 approximately 7245 cubic feet of air per minute was required. Com- 
 paring this result with the amount of air needed to carry away the 
 moisture we find that about seven times as much air is needed to fur- 
 nish heat for evaporation as is necessary to carry away the water 
 evaporated by this heat. If this extra six-sevenths of the air is allowed 
 to escape, much fuel value and much of the moisture-carrying capacity 
 is wasted. If six-sevenths of the air under the above assumed condi- 
 tions be returned to the furnace room and mixed with one-seventh of 
 fresh air and if one-seventh of this mixture after reheating and passage 
 through the evaporator be allowed to escape at 50 per cent or greater 
 relative humidity it is readily seen that the efficiency of the evaporator 
 is greatly increased. 
 
 This recirculation of the air is not only theoretically more efficient 
 but is of great value in practice for other reasons. If the air is too 
 dry and of high temperature, moisture may be taken from the surface 
 of the fruit more rapidly than it can effuse from the interior, resulting 
 in the formation of a hard shell on the surface, or ' ' case hardening, ' ' 
 which retards subsequent evaporation. If the humidity of the air is 
 relatively high, diffusion keeps pace with evaporation and case harden- 
 ing is prevented. A second advantage of the higher humidity of the 
 air is in preventing the over-drying of fruit ; because drying will cease 
 when the fruit and air arrive at the same relative moisture content. 
 Grapes tend to dry unevenly and many to over-dry in an atmosphere 
 of very low humidity ; that is, in very dry hot air. A third advantage 
 of the higher humidity is its tendency to reduce the injurious effects 
 
Bulletin 322 TH e evaporation OF grapes 427 
 
 of high temperatures on the fruit flavors. It is therefore possible to 
 use higher temperatures of drying with humid air than with dry air. 
 
 Because of the vital importance of controlling the humidity of the 
 air used in drying, prospective purchasers and manufacturers of 
 evaporators are advised to install in their plants some means of effect- 
 ively regulating the moisture content of the air. One of the most 
 effective methods of increasing the humidity of the air to the desired 
 degree, is that of returning a part of the exhaust air from the 
 evaporator to the furnace room where it is mixed with fresh air, 
 reheated and passed over the fruit again. By varying the propor- 
 tion of the recirculated air any desired degree of humidity may be 
 maintained. As already pointed out, recirculation of a part of the 
 air results in a great saying of fuel. 
 
 By way of summary it may be stated that (1) evaporation of 
 water from a free surface varies inversely as the relative humidity, 
 (2) directly as the time, (3) directly as the temperature, and (4) 
 as the square root of the air velocity. Dipped grapes more nearly 
 approach a free surface of water than do most fruits, because of their 
 small size and, therefore, the above relations will probably be more 
 nearly true for grapes than for other fruits. 
 
 (e) MISCELLANEOUS REQUIREMENTS 
 
 In addition to providing for the fundamental requirements of 
 adequate heat supply, air circulation and control of humidity, the 
 evaporator to be thoroughly satisfactory should include the following 
 features : 
 
 It should utilize its fuel efficiently. This means that the. transfer 
 of heat from the furnace to the air should be as complete as possible, 
 with very little of the heat escaping through the smoke stack. It 
 also means that radiation losses and losses through leaks should be 
 minimized. 
 
 The evaporator should be as convenient^ arranged as possible in 
 order to reduce labor costs to a minimum. This is a very important 
 point that some manufacturers have overlooked. Frequent shifting 
 of the trays in some evaporators greatly increases the labor cost: a 
 practice made necessary by uneven air distribution in the evaporator 
 and uneven drying of the fruit on the trays. 
 
 The evaporator should be so arranged in relation to the dipper, 
 spreading tables, sulfur house, stemmer, storage bins, etc., that the 
 fruit can be handled efficiently at all points. This will require careful 
 arrangement of the plant. 
 
428 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 It is the opinion of the writers that all evaporators representing 
 any considerable investment should be of fireproof construction. The 
 slight extra cost is an excellent investment. 
 
 The cost of an evaporator for grape drying must not be excessive 
 if the investment is to prove profitable. On the other hand, the 
 evaporator should not be of such cheap construction that its period 
 of usefulness will be excessively short. At 1919 prices for materials, 
 it is believed that a substantially constructed evaporator similar in 
 design to the University Farm Evaporator described below can be 
 erected and equipped for about $500 per fresh ton capacity per 24 
 hours. 
 
 IV. THE UNIVERSITY FARM EVAPORATOR 
 
 This evaporator was constructed primarily for the purposes of 
 conducting investigations in the drying of grapes and other fruits 
 upon a commercial scale and to convert the grape crop of the Univer- 
 sity Farm into a marketable product. It was also hoped that the 
 evaporator would serve as a model for growers who might wish to 
 build evaporators. 
 
 The discussion of the evaporator has been taken up under the 
 following topics: List of Materials and Cost of Construction, Descrip- 
 tion of the Evaporator as Used in 1919, Course Followed by Grapes 
 at Evaporator, and Suggested Revisions in Plan of University Farm 
 Evaporator. 
 
 (a) LIST OF MATEEIALS AND COST OF CONSTEUCTION 
 
 The materials, labor, and equipment entering into the construction 
 of the Davis evaporator are given in the following list : 
 
 Lumber : 
 
 6" X 6" rough redwood 152 
 
 2" X 6" S-2E Oregon pine 950 
 
 1" X 6" pine sheathing 3500 
 
 2" X 4" S-4-S Oregon pine 400 
 
 2" X 4" rough pine for yard track 360 
 
 1" X 4" T & G flooring 4100 
 
 2" X 8" rough pine 82 
 
 4" X 6" rough pine 88 
 
 4" X 4" rough pine 64 
 
 4" X 4" S-4-S Oregon pine for dipper 8 
 
 3" X 4" S-4-S Oregon pine for dipper 20 
 
 2" X 3" S-4-S Oregon pine for dipper 8 
 
 2" X 12" rough pine 300 
 
 19,000 redwood shingles 
 
 linear feet 
 
 $679. 
 
Bulletin 322 THE EVAPORATION OF GRAPES 429 
 
 2. Labor: 137% days at $5.00 per day 687.84 
 
 3. Plumbing materials for water and fuel supply 28.33 
 
 4. Electrical equipment and supplies: 
 
 (a) 1 7% h.p. 3-phase, 110-volt motor for fan $188.80 
 
 (b) 2 transformers, complete 97.50 
 
 (c) Wire 117.72 
 
 (d) 2 poles 18.80 
 
 (e) Switches, light sockets, insulators, cross arms, fuse 
 
 plugs, etc 25.95 
 
 448.77 
 
 5. Hardware: 
 
 (a) Heating pipe, 12" riveted: 6 pieces 8' long, 2 
 
 pieces 1' long, 2 pieces 20' long, 6 return bends, and 
 
 2 elbows $135.00 
 
 (b) 2 old boiler shells, 6' X 3' 100.00 
 
 (0) 1 California-Fresno large size gravity burner 22.50 
 
 (d) 1 Johnson whirlwind distillate burner, medium size .. 85.00 
 
 (e) 1 54" disc fan (American blower) 182.00 
 
 (/) 1 60" disc fan (American blower) 239.70 
 
 (g) 1 50-gallon cauldron '.'. 25.00 
 
 (h) 2 22" prune dipping baskets 17.00 
 
 (i) 1 set roller bearings for dipper 17.50 
 
 (j) 250' iron T-rail, 8 pounds per yard 39.57 
 
 (1c) 3 all steel lower dry-yard transfer trucks 56.25 
 
 (1) 13 wooden frame dry-yard trucks 73.13 
 
 (m) Hinges, nails, wire washers, furnace doors, etc 35.71 
 
 1028.36 
 
 6. Materials for 500 trays: 
 
 (a) Shook: 1000 pieces, 1%" X 1%" X 36"; 1000 pieces, 
 %" X iy 2 " X 33"; 1000 pieces, %" X 1%" X 36"; 
 1000 pieces, %" X %" X 33"; 500 pieces, %" X 1" 
 X 33"; 500 pieces, %" X %" X 34"; 1000 pieces, 
 1" X iy 2 " X 36" for side cleats to raise height of 
 trays $90.00 
 
 (6) Wire: 1200 linear feet, y 2 " mesh; 300 linear feet, %" 
 
 mesh; 300 linear feet, %" mesh 253.45 
 
 343.45 
 
 7. Cement, bricks, etc.: 
 
 (a) 128 sacks of cement $147.34 
 
 (b) 1000 second-hand brick (no charge) 
 
 (c) 400 fire brick 32.00 
 
 (d) 160 pounds of fire clay 4.80 
 
 (e) 3 loads of crushed rock 6.00 
 
 (/) 4 loads of sand 8.00 
 
 (g) 17 loads of creek gravel (no charge) 
 
 (h) 1^ barrels of lime 4.50 
 
 202.64 
 
 8. Paint for roof and stacks 41.75 
 
430 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 9. Thermometers: 
 
 (a) 1 recording thermometer $52.50 
 
 (&) 2 angle-stem Fahrenheit thermometers 39.60 
 
 92.10 
 
 10. Belting: 
 
 (a) 25' of 4" rubber belting (estimated) 13.25 
 
 (&) 10' of 4" leather belting, second hand (estimated) .... 10.00 
 (c) Belt lacing 25 
 
 23.50 
 
 11. Miscellaneous 5.91 
 
 Total $3582.64 
 
 The cost of an evaporator of this capacity (6 tons of fresh fruit 
 per charge) to the average builder at 1919 prices for materials would 
 be considerably less than the total given above for the following 
 reasons. The furnace room is twice as large as necessary and the 
 outside walls were given a special finish. One furnace and one burner 
 were found to be sufficient, although for experimental purposes two 
 of each were installed. The shed above the evaporator was built very 
 substantially of such design and finish as to compare favorably in 
 appearance with other buildings on the University Farm. A shed 
 less attractive in appearance but equally serviceable would probably 
 be built by the average grower. One fan was sufficient, although for 
 experimental purposes two were installed. However, these fans were 
 of an inexpensive type and one multivane fan to replace them would 
 cost as much as the two disc fans actually installed. The sulfur house 
 was built of cement; a wood sulfur house will answer. Taking all 
 such possible savings in cost into account it is believed that an evap- 
 orator of the same design and capacity as our plant could be built 
 and equipped for about $3000, or at a cost of about $500 per fresh 
 ton capacity per charge. 
 
 (6) DESCRIPTION OF THE UNIVERSITY FARM EVAPORATOR USED 
 
 IN 1919 
 
 The evaporator consists of a tunnel through which the cars loaded 
 with fruit are moved during drying and a fire-proof furnace room 
 for heating the air which is drawn or blown through the tunnel by 
 a fan. The remaining equipment is used for preparing the fruit for 
 drying or for packing the dried product. 
 
 The drying tunnel and dipping outfit are housed beneath a shed 
 approximately 60 feet long and 20 feet wide. The general appearance 
 of the complete plant may be seen from the accompanying photograph. 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 431 
 
 The tunnel is 33 feet long by 7 feet high by 6y 2 feet wide, inside 
 dimensions. The walls and ceiling are constructed of 1" X 4" tongue 
 and groove pine on an outside framework of 2" X 4" pine. The 
 floor is of cement and slopes toward the furnace room to aid in moving 
 the cars forward. The slope is 14 inch per foot ; for the type of cars 
 used, this slope could be considerably increased to advantage. 
 
 The location of the two doors may be seen from the accompanying 
 sketch. The door openings are 7 feet high by 64 inches wide and 
 each is closed by two tight-fitting folding doors. Transfer tracks 
 enter each door and connect with the tunnel track. The transfer track 
 rails are 42 inches apart and are ordinary dry-yard T rails of 8 pounds 
 
 Fig. 1. — View of the University Farm Evaporator. 
 
 per yard weight. The tunnel track rails are set 24 inches apart and 
 connect with the transfer tracks at each end of the tunnel. 
 
 An air return flue 1 foot high by 6y 2 feet wide and 33 feet long 
 rests above the drying tunnel. This connects with the tunnel outlet 
 by a door 1 foot by 6y 2 feet which folds upward and by a door of 
 the same size in the furnace room. The return flue is constructed 
 of 1" X 4" tongue and groove over 2" X 4" pine. It is used for 
 the return of a part of the exhaust air to the furnace room where it 
 may be mixed with fresh air, reheated, and recirculated. 
 
 The tunnel connects with the furnace room through a 60-inch 
 disc fan. A 54-inch disc fan is located at the other end of the tunnel. 
 A 7% h.p. electric motor is used to operate either fan. The fans and 
 motor have pulleys of such size that the 60" fan is operated at 300 
 r.p.m. and the 54-inch fan at about 350 r.p.m. When operated at 
 
432 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 the above speeds either fan should deliver 25,000 cubic feet of air 
 per minute (catalog rating). The two fans were installed merely 
 for the purpose of comparing a blast fan with a suction fan. 
 
 The furnace room is 16 feet long by 12 feet wide by 12 feet high, 
 outside dimensions. The walls and roof are of 6-inch reinforced con- 
 crete. Two old boiler shells, each 6 feet long by 3 feet in diameter, 
 open at one end for installation of burner, and connected at the other 
 end to a 12-inch pipe, have been placed on opposite sides of the furnace 
 room, as shown in figure 2. Each furnace is connected to three lengths 
 of 12-inch heavy gauge sheet iron pipe which is led back and forth 
 above each furnace before connecting to the smoke stack extending 
 20 feet above the furnace room. The hot gases from the furnace 
 must travel a distance of 40 feet through the radiating pipes in the 
 furnace room before reaching the stack. One furnace is fitted with 
 a gravity burner and the second with an air-blast burner. Fuel is 
 supplied to the burners through ^-inch pipes connected to a 110- 
 gallon distillate drum placed on a platform 5 feet above the ground. 
 In the wall of the furnace room opposite the tunnel are located two 
 sets of three doors each for the admission of fresh air to the furnace 
 room and tunnel. One set of doors is opposite each furnace. Each 
 door is about 28 inches by 20 inches in size. (See figs. 1 and 2.) 
 The amount of air admitted to the evaporator is regulated by adjust- 
 ing these doors. 
 
 The dipping equipment is located under the east end of the 
 evaporator shed. It consists first of a 50-gallon prune-dipping 
 cauldron mounted over a brick furnace in which is burned coal or 
 wood to keep the lye solution in the kettle at the boiling point. 
 Adjacent to this kettle and at the same height above the floor (33 
 inches) is a cement vat of the same size and shape as the cauldron. 
 This vat holds the water used in rinsing the grapes after dipping, and 
 is equipped with a drain pipe and fresh water supply. The dipping 
 machine consists of the following parts. Two 22-inch prune-dipping 
 baskets are hung at the ends of 3" X 4" pieces which are 5% feet 
 long and pivoted on two 4" X 4" pieces, which in turn are attached 
 to a 6" X 6" upright piece and supported by 2" X 4" pieces, as shown 
 in figure 2 section. The 6" X 6" upright pieces rest on a roller bear- 
 ing pivot. The baskets are counterbalanced by boxes of sand. The 
 end of each basket support carrying the sand box is connected to a 
 pivoted handle so that the basket may be depressed into the lye 
 solution or rinse water by merely raising this handle. The handle 
 is also used in swinging the loaded basket from the loading chute to 
 the lye kettle; from lye kettle to the rinsing vat, from the rinsing 
 
Bulletin 322 
 
 THE EVAPORATION OP GRAPES 
 
 433 
 
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 vat to the tray loading table, and from this point back to the loading 
 chute. This dipping machine is patterned closely after the ''Sutter 
 County Merry-Go-Round Dipper" used for many years for dipping 
 Sultanina grapes before drying and may be purchased in complete 
 form from manufacturers, although the outfit is not complicated and 
 can be built locally. The ordinary prune dippers of various forms 
 may be used successfully, but must be equipped for rinsing the dipped 
 grapes. Continuous dipping machines for grapes are available. 
 
434 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 A platform. 16' X 12' and 2 feet high is placed outside the evapo- 
 rator shed but adjacent to the dipping outfit for receiving the fresh 
 grapes. I A concrete sulfur house, 7 feet wide by iy 2 feet high by 
 8 feet long, inside measurements, is located a short distance from 
 the shed. It is equipped with tight-fitting folding doors; a 6-inch 
 adjustable ventilator in roof ; a sulfur pit, 8 inches deep and 8" X 12" 
 in size, and tracks for drier cars. It will hold two loaded cars. 
 
 Thirteen wooden frame dry-yard trucks were used. The evapo- 
 rator held eight cars when filled to capacity and each car held 42 trays 
 of 35 pounds of grapes each, making a total of six tons of fresh grapes 
 per charge. The frames on the trucks were placed at right angles 
 to the tracks upon which the cars operate. This position of the frames 
 makes each truck six feet wide and three feet long and therefore only 
 one track is necessary in the tunnel. The transfer cars are of steel 
 construction throughout and of the type used in evaporators in Fresno 
 County in which raisins are dried for cap stemming. Both the 
 evaporator and the transfer cars were very satisfactory, except for 
 the difficulty in moving the cars because of the friction on the axles. 
 Roller-bearing wheels would be much more desirable but are costly. 
 
 The trays are three feet square. Each side is constructed of one 
 piece, 36" X 1%" X 1%" and one piece, 33" X %" X iy 2 " J each end 
 consists of one piece, 36" X %" X 1%" and one piece, 33" X %" 
 X %"• The tray is braced through the center by one piece, 33" X %" 
 X 1", and one piece, 34" X %" %'•' Most of the trays were made 
 with screen bottoms held between the various pieces of shook listed 
 above. (See fig. 9.) The most satisfactory trays were of the above 
 construction for the frame but with narrow wooden slats substituted 
 for the screen. Screen of 14" mesh is much better than that of V 2 " 
 mesh. It was found necessary to raise the height of the sides of the 
 trays by nailing to them strips 1" X IV2" X 36" in size in order to 
 give sufficient space for passage of air. 
 
 (c) COUESE FOLLOWED BY GRAPES AT EVAPORATOR 
 
 The grapes were ordinarily treated as follows : The fresh grapes 
 were unloaded at the receiving platform and weighed. They were 
 then emptied into the chute from which they fell into the dipping 
 basket. The basket was immersed in the boiling lye solution, which 
 varied in strength, from y 2 per cent to 3 per cent lye according to 
 the variety of grapes. After 5 to 40 seconds' immersion in the lye 
 solution, the time varying with the variety, the grapes were plunged 
 into cold water to remove adhering lye. The basket of rinsed grapes 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 435 
 
 was then transferred to an empty tray and the grapes spread evenly 
 by hand. The loaded trays were stacked in two tiers of 21 trays each 
 on a car. The loaded car was transferred to the sulfur house and 
 exposed to sulfur fumes for about 30 minutes. In some cases sul- 
 furing was omitted. The car of fruit then entered the tunnel at the 
 end opposite the furnace room where the air was moister and 20 to 
 30 degrees cooler than at the furnace end. As each car of dried grapes 
 
 Fig. 3. — Evaporator car loaded with trays of freshly dipped grapes, 
 transfer car beneath evaporator car. Unloading slat bottom tray at right. 
 
 Note 
 
 was removed through the side door at the furnace end of the tunnel, 
 the remaining cars were moved forward the length of one car, 
 and a fresh car was inserted at the exhaust end. The dried grapes 
 were allowed to cool and were then transferred to sacks for shipment 
 without stemming. 
 
 All of the above steps were varied greatly during the various 
 experiments. 
 
436 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 
 
 (d) SUGGESTED EE VISIONS IN PLAN OF UNIVERSITY FARM 
 
 EVAPORATOR 
 
 The evaporator in its first form proved successful. However, 
 the past season 's experience showed that certain additions and changes 
 are desirable in order to increase the efficiency of the plant and the 
 convenience of operation. The sketches shown in figures 4 and 5 
 indicate the construction of an evaporator recommended to growers. 
 It resembles the University Farm evaporator very closely in outline 
 and appearance, but includes in its construction the modifications and 
 additions noted below. Practically all of the suggested changes have 
 been made and may be seen by those who wish to visit the University 
 Farm at Davis. 
 
 1. Furnace Room. — One furnace, 10' to 12' long by 3' in diameter, 
 equipped with a medium-size air-blast distillate burner is sufficient. 
 The furnace room should be of fire-proof construction, e.g., concrete, 
 brick, or tile and should be about 14' long by 8' wide by 11' high, 
 inside dimensions. Attached to the furnace are nine lengths of 12-inch 
 heavy gauge black iron pipe distributed as shown in figure 5, giving 
 a total length of radiating pipe, including connections, of approxi- 
 mately 120 feet. The pipes are arranged in three tiers of three pipes 
 each. The individual pieces are joined together vertically by return 
 bends and horizontally by headers or T connections. A T connects 
 the smokestack to the radiating pipe system. This is fitted with two 
 dampers by means of which the gases of combustion may be allowed 
 to flow out through the stack or into the furnace room as desired. 
 This arrangement of pipes and clampers gives approximately three 
 times the heating surface furnished by the first installation for one 
 furnace and also makes it possible to use the gases of combustion 
 directly in drying. 
 
 At each side of the furnace in the end wall of the furnace room 
 is situated an air intake door. Each is one foot wide and one and a 
 half feet high. Another air intake door of same size is located two 
 feet above the furnace. All doors should be sliding to enable regula- 
 tion of air intake. (See revised plan, fig. 5.) The evaporator now 
 includes essentially these features. 
 
 2. Connection of Furnace Room to Tunnel. — No fan to be located 
 between the furnace room and tunnel and the opening connecting the 
 two to be of same size as cross section of tunnel ; that is, 7 feet high 
 by 6V2 feet wide. 
 
 3. Fan, — The two disc fans of the present installation to be 
 replaced by a top vertical discharge multivane fan with fan wheel 
 
Bulletin 322 
 
 THE EVAPORATION OP GRAPES 
 
 437 
 
438 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 36 inches in diameter and connected to a iy 2 horsepower motor by 
 belt and pulleys to give about 300 r.p.m. The fan to be located at 
 air exit end of tunnel. Intake of fan to be connected by sheet metal 
 housing to tunnel outlet. The discharge of fan to be connected to 
 return flue of tunnel and also arranged to discharge into the open 
 air as shown in figure 5 ; these two connections to be equipped with 
 adjustable dampers so that any proportion of the exhaust air may 
 be returned to the furnace room or discharged into the open air. 
 This fan has now been installed. 
 
 4. Air Locks. — During the past season considerable heated air was 
 lost and drying was interrupted when the doors of the tunnel were 
 opened to insert or remove cars, or to enter the tunnel to take obser- 
 vations on temperature, etc. It is, therefore, very desirable to build 
 compartments at entrance and exit of the tunnel as shown in figure 4. 
 In using the compartment at the entrance end of the tunnel the car 
 of fresh fruit enters the compartment through the folding doors at the 
 side of the compartment. The operator enters with the car and closes 
 the doors. He then opens the sliding door connecting the air lock 
 with the tunnel, places the car in the tunnel and closes the sliding 
 door. Finished cars are removed in a similar manner. Practically 
 no heated air is lost or cold air drawn in during the above operations. 
 
 The air lock for entrance of fresh fruit consists of a compartment 
 5% feet wide, 7 feet high, and 7% feet long, inside dimensions. Two 
 folding doors form the side of the air lock toward the dipping outfit 
 and a second set of doors opens toward the sulfur house. The lock 
 for removal of cars of dried fruit is of the same dimensions and con- 
 struction, except that it is equipped with doors at the ends only. 
 Both locks are constructed of 1" X 4" tongue and groove pine over 
 a frame of 2" X 4" pine. These may now be seen in place at the 
 University Farm. 
 
 5. Dipping Tank. — It was very difficult to maintain the lye solu- 
 tion at the boiling point during the 1919 season because of the small 
 size of the dipping cauldron, 50 gallons, and necessity of using wood 
 or coal instead of oil for fuel. The 50-gallon kettle has been replaced 
 by a sheet metal tank 6' long by 3' wide by 1%' deep mounted in a 
 fire brick furnace equipped with a medium-size blast-type distillate 
 burner. The above tank will hold about 200 gallons of liquid and 
 presents a long surface to the furnace flame. The experience of others 
 has proved that a furnace and dipping tank of this type can be 
 maintained at the boiling point during continuous operation. 
 
 6. Rinsing Vat. — The present 50-gallon rinsing vat could be in- 
 creased to 200 gallons in size to advantage. This would require less 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 439 
 
 frequent changing of rinse water. A sheet metal drain over the 
 space between the dipping vat and the rinsing vat for return to the 
 dipping vat of the lye solution which drips from the dipping basket 
 would reduce the loss of lye solution. 
 
 7. Track System. — The track now located under the shed at the 
 south side of the tunnel will be moved outside the shed and will 
 
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 Fig. 5. — Sections showing fan connections, lye tank, and furnace room, of 
 revised University Farm evaporator. 
 
 connect to two transfer tracks as shown in figure 4. This track will 
 be continued to the west end of the shed where it will connect to a 
 transfer track which in turn connects to the track between the dipping 
 outfit and tunnel entrance. This arrangement will make it possible 
 to move loaded and empty cars to and from the tunnel without inter- 
 ference. 
 
 8. Observation Windows. — Six or seven small port holes about 
 one foot square have been cut in the north wall of the tunnel at such 
 points that each car of fruit in the tunnel may be observed and 
 samples removed. The windows are closed by air-tight doors. 
 
440 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 9. Double Walls for Tunnel. — The first tunnel walls were made 
 of one thickness, 1" X 4" T & G over 2" X 4" pine outside frame. 
 The frame has been covered with T & G over building paper, to make 
 the walls airtight and to reduce radiation losses. 
 
 10. Tray Guides on Trucks. — Difficulty was encountered during 
 the past season in holding the trays on the trucks in a perfectly 
 vertical position. Upright guides of 2" X 4" have been placed in the 
 
 Fig. 6. — Photographs of an evaporator truck equipped with upright guide-posts 
 for trays. 
 
 center of each car frame and the trays will be stacked against this 
 frame. The tunnel is wide enough to permit this change. See figure 6 
 which illustrates such a car used in the Pearson evaporator. 
 
 11. Trays. — Most of the screen bottom trays will be converted into 
 slat bottom trays by replacing the screens with narrow wooden slats 
 placed about % of an inch apart. The sides of all trays will be 
 increased in height by the addition of pieces 36" X 1" X 1%" to 
 trays not already so equipped. 
 
 12. Air Baffles. — To prevent the passage of heated air beneath the 
 cars during the past season pieces of canvas were nailed to the car 
 frames. These extended from the level of the track to the bottom 
 of the cars. These will be replaced in part by two enclosed wooden 
 platforms on the tunnel floor, one on each side of the tunnel track, 
 
Bulletin 322 TH e EVAPORATION OF GRAPES 441 
 
 of such height that the frames of the trucks will barely clear them. 
 These platforms will be closed so that the air will not be permitted 
 to flow beneath the car frames between the tracks and walls of tunnel. 
 The canvas will be retained on the car frame between the tracks only. 
 It is essential that all possible precautions be taken to force the 
 air to flow over the trays. Air, like water, follows the channels of 
 least resistance, and instead of flowing over the trays tends to follow 
 all possible passages at the sides of the cars, beneath the trucks or 
 above the topmost tray. 
 
 V. COST OF OPERATION 
 
 Because of the fact that the University Farm evaporator during 
 the past season was employed in the drying of numerous small experi- 
 mental lots of grapes, our cost of operation was abnormally high. 
 Therefore, due allowance must be made for this fact in considering 
 our data on costs of operation given in the following summary: 
 
 1. Total tons of fresh grapes handled at evaporator 52.18 
 
 2. Total tons of dry grapes handled at evaporator 15.65 
 
 3. Labor cost per fresh ton $ 8.102 
 
 4. Labor cost per dry ton $27,015 
 
 5. Labor cost of dipping per dry ton $ 8.78 
 
 6. Labor cost of unloading trays per dry ton $10.52 
 
 7. Labor cost of general work per dry ton $ 5.69 
 
 8. Labor cost of night operator per dry ton $ .63 
 
 9. Cost of fuel per green ton (stove distillate at 8c per gallon) $ 6.23 
 
 10. Cost of fuel per dry ton (stove distillate at 8c per gallon) $21.52 
 
 11. Cost of electric light and power per green ton of grapes $ .50 
 
 12. Cost of electric light and power per dry ton of grapes $ 1.73 
 
 13. Containers for dried product (second-hand barley sacks at 8c each), 
 
 cost per ton of dry grapes $ 2.00 
 
 14. Interest and depreciation at 10% (on $3500), cost per green ton.... $ 7.71 
 
 15. Interest and depreciation at 10% (on $3500), cost per dry ton $22.36 
 
 16. Total cost per green ton $28,562 
 
 17. Total cost per dry ton $74,620 
 
 18. Total cost per green ton, exclusive of depreciation $20,852 
 
 19. Total cost per dry ton, exclusive of depreciation $52,260 
 
 If the interest and depreciation are included in the cost of opera- 
 tion the total cost per dry pound of grapes was in excess of 3y 2 c and 
 per fresh pound over l^c. Because of our short operating season 
 the item of interest and depreciation is excessively high. If it is 
 omitted from the calculations the costs become approximately 2%c 
 per dry pound and slightly over lc per fresh pound. It is certain 
 that by conducting the University Farm evaporating plant upon a 
 commercial basis and by adopting the modifications in methods of 
 
442 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 operation that last season's experience have shown to be desirable, 
 the costs given above could be very materially reduced. 
 
 IV. RESULTS OF INVESTIGATIONS 
 
 As many as possible of the different processes involved in the 
 drying of grapes in the sun and in evaporators were investigated. A 
 great deal of information was obtained, although time did not permit 
 the completion of all the experiments undertaken nor the solution 
 of all of the problems presented. At least one more season's work is 
 necessary to obtain the data needed. 
 
 Because of the voluminous nature of the original data, even when 
 condensed by tabulation, it is necessary to present the results in 
 summarized form. Investigators or others who may be interested in 
 a detailed study of our experimental results are invited to inspect 
 the data filed in the projects in our office. 
 
 The results will be taken up as nearly as possible in the sequence 
 in which the various evaporation processes occur. 
 
 (a) DIPPING 
 
 The dipping of grapes in a hot lye solution before drying has 
 been practised for many years in the sun-drying of Sultanina (Thomp- 
 son Seedless) grapes to hasten the rate of drying. Its use in the 
 treatment of Muscat grapes, table grapes, and many varieties of wine 
 grapes was thoroughly tested. 
 
 It was found that different varieties exhibited a most remarkable 
 difference in their behavior in the dipping solution. Sultanina, Tokay, 
 Emperor, Zalbalkanski, Palomino, Black Morocco, and Cornichon gave 
 excellent results when dipped in a boiling solution of y 2 per cent to 
 1 per cent lye followed by rinsing in water. The skins of these grapes 
 were checked into numerous minute cracks extending from the stem 
 toward the apex of the berries. Practically all berries on the bunch 
 responded to the dipping and the checks were well distributed and 
 uniform in size. Solutions stronger than 1 per cent lye tended to 
 cause slipping of the skins of some of the berries. Of the grapes listed 
 above, the Sultanina gave the best results, the berries of this variety 
 requiring only 3 to 5 seconds' immersion in the boiling lye solution. 
 Tokays required 10 to 15 seconds, and the checks were somewhat 
 deeper and longer than those on the Sultanina. The same character- 
 istics held for the other large varieties named above. 
 
 Most of the wine grape varieties, such as Petite Sirah, Zinfandel, 
 Carignane, Alicante Bouschet, St. Macaire, Mondeuse, Crabbe's Black 
 
Bulletin 322 TH e EVAPORATION OF GRAPES 443 
 
 Burgundy, Barbera, Valdepenas, Refosco, Lagrain, Gros Mansenc, 
 Burger, Franken, and Johannesburg Riesling, Sauvignon Vert, Sau- 
 vignon Blanc, and West's White Prolific were very difficult to check 
 by dipping. It was necessary with these varieties to use a dipping 
 solution of 2 to 3 per cent lye (17 to 25 pounds of granular sodium 
 hydroxid — soda lye — per 100 gallons of water) and to maintain this 
 solution at the boiling point. Weak solutions had no apparent effect 
 except to remove the bloom. Many driers of wine grapes became 
 discouraged because of the difficulty in obtaining satisfactory results 
 and dried their grapes without dipping, thereby greatly increasing 
 the time necessary for drying. The secrets of success lie in using a 
 lye dip of at least 2 per cent active lye and to keep the solution actively 
 boiling. Even under these favorable conditions, it was found that 
 from 20 to 40 seconds' time was necessary for the grape varieties 
 listed above. These varieties developed deeper cracks than those 
 given in the first list above. The cracks were unevenly distributed 
 and tended to extend at right angles to the vertical axis of the grapes 
 rather than parallel to that axis. Many berries became softened and 
 deeply cracked while others on the same bunch exhibited no apparent 
 effect of the lye. The berries of some varieties tended to shatter badly 
 from the bunches. In spite of this defect, however, the fact that 
 dipping shortened the time of drying by one half was held sufficient 
 reason for dipping. 
 
 Muscat and Malaga grapes, because of their tough, thick skins, 
 were the most difficult grapes of all to check by lye dipping. The 
 berries tended to burst before the lye checked the skins. The cracks 
 were deep and unevenly distributed. Nevertheless, dipping of these 
 varieties is necessary for rapid drying. A 2 to 3 per cent solution 
 of lye at 212° F. for 30 to 50 seconds was necessary for effective 
 results. 
 
 It was found practically impossible to check the skins of eastern 
 varieties such as Concord, Isabella, etc. 
 
 The effect of dipping on the appearance of the finished product 
 is very noticeable. Dipping removes the natural bloom of the grapes 
 and imparts a glossy appearance. Raisins from dipped grapes are 
 more sticky than those from undipped grapes. The flavor is not 
 materially affected unless the lye is not thoroughly removed by rinsing 
 in clean water before drying. Where rinsing is not well done, the 
 raisins will possess a distinct although not especially disagreeable 
 "lye" flavor. Dipped grapes produce a raisin of sweeter taste than 
 undipped because some of the grape acid is neutralized by the lye. 
 
444 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 Table 1. — Effect of Dipping on Eate of Evaporation of Geapes 
 
 Burger grapes, No. 2739 Tokay grapes, No. 2737 
 
 Time in 
 hours 
 
 Tempera- 
 ture 
 
 Weight of 
 grapes 
 
 undipped, 
 grams 
 
 Weight of 
 grapes 
 dipped, 
 grams 
 
 Time in 
 hours 
 
 Tempera- 
 ture 
 
 Weight of 
 grapes 
 
 undipped, 
 grams 
 
 Weight of 
 grapes 
 dipped, 
 grams 
 
 
 
 140° F. 
 
 1500 
 
 1500 
 
 
 
 145° F. 
 
 1200 
 
 1200 
 
 4.5 
 
 140° F. 
 
 1272 
 
 1038 
 
 2 
 
 145° F. 
 
 1145 
 
 935 
 
 6 
 
 140° F. 
 
 1192 
 
 853 
 
 6 
 
 145° F. 
 
 980 
 
 515 
 
 8 
 
 140° F. 
 
 1134 
 
 728 
 
 8.5 
 
 145° F. 
 
 924 
 
 422 
 
 9 
 
 140° F. 
 
 1082 
 
 633 
 
 10 
 
 145° F. 
 
 813 
 
 317 
 
 15.5 
 
 140° F. 
 
 902 
 
 408 
 
 12.5 
 
 145° F. 
 
 728 
 
 273 
 
 17 
 
 140° F. 
 
 802 
 
 363 
 
 16.5 
 
 145° F. 
 
 630 
 
 233 
 
 
 
 
 
 19.5 
 
 145° F. 
 
 580 
 
 225 
 
 
 
 
 
 23.5 
 
 145° F. 
 
 554 
 
 227 
 
 
 
 
 
 32 
 
 145° F. 
 
 518 
 
 220 
 
 
 
 
 
 38 
 
 145° F. 
 
 378 
 
 212 
 
 
 
 
 
 40 
 
 145° F. 
 
 325 
 
 
 The dipping of the fresh grapes before drying is remarkable in 
 its effect upon the rate of drying. Numerous tests upon the rate of 
 drying of dipped and undipped grapes both in the evaporator and in 
 the sun were made. Table 1 and the curves in figure 7 illustrate this 
 point. The data of table 1 were obtained by drying dipped and 
 undipped grapes on small screen-bottom trays in the laboratory 
 evaporator at Berkeley. This evaporator is so constructed that a 
 strong current of heated air is driven across the trays by means of a 
 fan. Because of the high velocity of the air, the rate of drying was 
 rapid. This small evaporator is very useful for experimental purposes 
 because of the fact that the temperature and humidity of the air used 
 in drying may be easily regulated. 
 
 The results shown in figure 7, curve II, were obtained by weighing 
 dipped and undipped lots of Carignane grapes during the drying of 
 these grapes on field trays in the sun. 
 
 From the table and curves it may be seen that the dipped Tokay 
 grapes were thoroughly dried in 16y 2 hours while the undipped grapes 
 of the same variety were not sufficiently dried after 40 hours. Dip- 
 ping in this case more than doubled the speed of drying. Similar 
 results were obtained with Burger grapes and several other varieties 
 in laboratory tests. 
 
 In the sun-drying tests the dipped grapes lost 65 per cent of their 
 weight and were sufficiently dried at 20 days, while 33 days were 
 required for the undipped grapes to reach the same degree of dryness. 
 Dipping in this case reduced the time of drying by approximately 
 one third. 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 445 
 
 In addition to the experimental results given above, measurements 
 were made to determine the quantity of lye used in dipping different 
 varieties of grapes. It was found that varieties such as Petite Sirah, 
 
 
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 Fig. 7. — I, Curves illustrating- effect of dipping on rate of drying of Tokay- 
 grapes in an evaporator. II, Effect of dipping on rate of drying Carignane grapes 
 
 Semillon, and Zinfandel, with tough skins, required about five pounds 
 of lye per ton of fresh grapes. Of this quantity about one pound was 
 
446 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 lost in the rinsing water while the remaining four pounds represent 
 lye neutralized by the grapes when the grapes were immersed for 
 30 seconds in the lye. 
 
 Observations were also made upon the amount of lye lost in dip- 
 ping Petite Sirah grapes at the Pearson evaporator at Yountville. 
 The grapes were immersed in lye of 3.2 per cent sodium hydroxid 
 for 20 seconds. After dipping 2800 pounds of grapes and adding 
 water to the vat to replace that lost mechanically and by evaporation, 
 it was found that the lye concentration had decreased .6 per cent. 
 This corresponds to a loss of 14 pounds of lye per ton of grapes. Of 
 this, one sixth, or 2.3 pounds, was neutralized by the grapes and the 
 remainder, 11.7 pounds, was lost in the rinsing vat. Based upon a 
 dipping period of 20 seconds, the average amount of lye neutral- 
 ized by such varieties as Petite Sirah at Davis and at the Pearson 
 evaporator was approximately 2.5 pounds per ton of fresh grapes. 
 Theoretically this should reduce the acidit}^ of the grapes approxi- 
 mately .25 per cent, 
 
 The smaller loss of lye in rinsing in our tests was probably due to 
 the fact that the dipped grapes were more thoroughly drained before 
 rinsing and that a stronger lye solution was used at the Pearson plant. 
 Our tests demonstrated that the loss of lye in rinsing was greater with 
 the stronger lye solutions. 
 
 Thin-skinned varieties, such as the Sultanina, required about 1% 
 pounds of lye per fresh ton of grapes. Of this, about half a pound 
 was lost in the rinse water and 1*4 pounds was neutralized by the 
 grapes. 
 
 Grapes are coated with a waxy bloom which disappears in the lye 
 dip. It is probable that this substance neutralizes considerable quan- 
 tities of the lye because it is a wellknown fact that some fruit waxes 
 possess the power of neutralizing lye. 
 
 It was observed that shrivelled over-ripe grapes as well as grapes 
 that had wilted by standing in boxes several days during warm 
 weather were much more difficult if not impossible to check in the lye 
 solution, thereby necessitating a longer time to dry. Grapes that had 
 stood several days in lug boxes and had become moldy or had started 
 to ferment, softened and shattered badly from the bunches in dipping. 
 For these reasons grapes should be dipped as soon as possible after 
 picking. 
 
 A record of the labor cost of dipping, spreading and stacking the 
 trays of grapes was kept for the entire season. The following table 
 summarizes some of the results obtained. 
 
Bulletin 322 THE evaporation of grapes 447 
 
 Table 2. — Labor Eecord of Dipping and Spreading Grapes 
 
 Pounds dipped per Labor cost per Labor cost per 
 
 Variety hour fresh ton dry ton 
 
 Sultanina 2166 $1.49 $5.08 
 
 Tokay 1808 1.79 6.09 
 
 Muscat 1241 2.61 8.19 
 
 Gros Mansenc 1151 2.81 8.31 
 
 Zinfandel 1073 3.02 10.24 
 
 Petite Sirah 1005 3.22 10.47 
 
 Average for season, all varieties $2.62 $8.78 
 
 Because of the fact that much of the work wus done with small 
 experimental lots the labor costs of dipping were abnormally high 
 and it should be possible under average commercial conditions to 
 greatly reduce the costs given in table 2. The figures also include 
 the cost of spreading the fruit and stacking the trays on the drier 
 trucks. Two men were used in operating the dipper and two in 
 spreading and stacking trays. Therefore, to obtain a fair idea of the 
 labor cost of dipping only, the above figures should be divided by two, 
 thus giving an average labor cost of dipping for the season of $1.31 
 per fresh ton or $4.39 per dry ton, or $0.00214 (%c) per dry pound. 
 
 About five to six gallons of stove distillate per hour at 6c to 8c 
 per gallon was required to maintain a tank containing approximately 
 400 gallons of lye solution at the boiling point at the Pearson plant. 
 The total cost of fuel per hour varied from 30c to 48c. This corre- 
 sponds to a cost of approximately 15c to 24c per fresh ton of Petite 
 Sirah or similar grapes. 
 
 (6) SUN-DRYING VERSUS EVAPORATION 
 
 A very important question before the fruit growers of California 
 concerns the relative merits of drying fruit in the sun and in evapora- 
 tors. Which of these two methods will prove the more profitable to 
 the growers depends upon several factors, the most important of 
 which are: (1) relative yields of dry product, (2) quality of dry 
 product, (3) cost of drying, (4) initial investment and depreciation. 
 
 A number of experiments were undertaken at Davis to compare 
 the yields of several varieties of grapes dried in the sun with lots of 
 the same varieties dried in the evaporator. It is to be regretted that 
 the results were not absolutely conclusive. The difference in yield by 
 the two methods is so small that a large number of tests will be neces- 
 sary to definitely solve the problem. The results of the past season's 
 tests are summarized in the following table: 
 
448 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 
 
 Table 3. — Summary of Results of Yields of Moisture-Free Product per 
 100 Pounds Fresh Grapes 
 
 By sun-drying, By evaporator, 
 
 pounds pounds 
 
 Muscat grapes 25.31 25.93 
 
 Sultanina grapes 27.79 26.71 
 
 Tokay grapes 24.10 23.51 
 
 Zinfandel grapes 35.02 27.59 
 
 Lagrain grapes 29.88 33.11 
 
 Carignane grapes 27.42 23.60 
 
 Semillon grapes 27.93 28,35 
 
 Average, all varieties 28.26 25.22 
 
 An examination of the two tables indicates that Semillon, Lag-rain, 
 and Muscat varieties gave higher yields in the evaporator, while the 
 Carignane, Zinfandel, Tokay, and Sultanina varieties gave higher 
 yields by sun-drying. Averages of all tests gave a slightly higher yield 
 for the sun-drying method. 
 
 The only conclusion which seems warranted is that our experiments 
 indicate little difference in the yields of moisture-free product obtained 
 by sun-drying and evaporation. If these results are confirmed by 
 future tests it will mean that the choice between the two methods will 
 have to be made on relative quality of the finished product, cost of 
 operation, and prices received for the dried fruit, rather than upon 
 comparative yields. 
 
 The above conclusions are based upon the relative yields of moist- 
 ure-free product. This is obtained by means of a calculation based 
 upon the drying ratio and moisture content of the finished product. 
 It affords the only accurate basis of comparison. However, a compari- 
 son of an average of the drying ratios given in table 3 is of interest. 
 The average drying ratio for sun-dried grapes was 3.04 as against 3.21 
 for the evaporated grapes, a difference of .17 or 5.44 per cent greater 
 yield in favor of the sun-drying. This would indicate that there was 
 at Davis a tendency to dry the grapes in the evaporator to a lower 
 moisture content with consequent lower yield of dried product. The 
 fact that the degree of drying can be accurately regulated in the 
 evaporator is a strong point in its favor. More will be said about the 
 moisture content of dried grapes later. 
 
 White grapes dried in the evaporator were lighter in color than 
 the same grapes dried in the sun and to produce a raisin of very light 
 color a much shorter time of sulfuring was required for the grapes 
 dried in the evaporator. Sultanina grapes sulfured for a half hour 
 and dried in the evaporator were as light in color as the same variety 
 sulfured for three hours and dried in the sun. 
 
Bulletin 322 THE EVAPORATION OF GRAPES 449 
 
 Evaporated grapes retained more of the fresh grape flavor and 
 developed much less of a caramel or "raisin" flavor than the same 
 varieties of grapes dried in the sun. Muscat grapes dried in the 
 evaporator possessed a pronounced fresh Muscat flavor and were more 
 acid or tart to the taste than sun-dried Muscats. The color and flavor 
 of sun-dried Muscat raisins has been firmly established in the mind 
 of the consuming public by extensive national advertising. Therefore, 
 although the flavor of the Muscat raisin made by evaporation more 
 nearly resembles that of the fresh fruit, this difference in flavor from 
 that of the sun-dried article makes it doubtful whether its merits 
 would be appreciated by the consumer unless it were well advertised. 
 Should over-production of Muscat raisins ever occur, the drying of a 
 part of the crop in artificial evaporators in order to produce a raisin 
 of special quality might well be considered. 
 
 Red-wine grapes, such as Zinfandel and Petite Sirah, dried in the 
 sun were apparently as deep in color and of as good quality as the 
 same varieties dried in the evaporator, but when the color and flavor 
 of the juices obtained by pressing the dried grapes after soaking in 
 water were compared the juice from the evaporated grapes was deep 
 red in color and of pleasing flavor while that from the sun-dried grapes 
 was of a brown color and poorer in flavor. These observations are 
 confirmed by tests made upon red-wine grapes dried in the sun at the 
 Kearney Vineyard several years ago. It would appear that sunlight 
 injures the color or that chemical changes taking place at the low 
 temperatures of sun drying may cause oxidation and browning of the 
 color. If dried wine grapes are exported to foreign countries for wine 
 making the evaporated product will be found much superior to the 
 sun-dried. 
 
 The relative costs of evaporation and sun-drying have not been 
 definitely determined by one season's operation, because the operation 
 of grape evaporators during the past season was largely experimental 
 in nature and methods were not standardized. Our experience would 
 indicate that the cost of evaporating dipped grapes is no greater than 
 in sun-drying except for the cost of fuel and power. The labor cost 
 is at least no greater for evaporation and is probably less than for 
 sun-drying dipped grapes. The labor cost involved in drying grapes 
 on field trays in the vineyard is doubtless less than that necessary in 
 evaporating, but the higher quality and price of evaporated wine 
 grapes more than compensate for the extra cost of evaporation. This 
 fact was well established during the 1919 season when a difference of 
 as much as 4c per pound existed in favor of the evaporated grapes. 
 
450 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 
 
 The preference for the evaporated product is said to be even more 
 pronounced at the present time than it was during the past fall. 
 
 The fact that drying in the sun incurs danger of loss by rain 
 damage is another reason for favoring evaporation. 
 
 (c) SULFURING 
 
 Grapes of several different varieties were sulfured for various 
 lengths of time and were subsequently dried in the sun or in the 
 evaporator. It was found that less than half as long a period of 
 exposure to sulfur fumes was necessary for the grapes dried in the 
 evaporator. This is probably because the period of drying in the 
 evaporator is so much shorter than that necessary for sun-drying and 
 because the higher temperature of the evaporator reduces the tendency 
 of the fruit to darken. 
 
 Red-wine grapes which were dried in the sun without sulfuring 
 gave a juice of brown color on extraction with water; but the same 
 varieties of grapes which were sulfured for one hour or longer before 
 drying in the sun gave a water extract of red color and pleasing flavor. 
 Therefore, it is advised that red wine grapes that are to be dried in 
 the sun be sulfured for about one hour before drying. 
 
 It was found that grapes dried in the evaporator or sun after three 
 hours' sulfuring fermented readily when ground and mixed with 
 water; that is, this amount of sulfuring was not sufficient to prevent 
 the use of such grapes for vinegar making in the United States or 
 for wine making when exported to foreign markets. 
 
 The color of all grapes dried in the evaporator was improved by 
 a short sulfuring. Thirty minutes' exposure to sulfur fumes was 
 sufficient for most white varieties and for Tokay and other grapes 
 of pink color. Fifteen to twenty minutes improved the color of red- 
 wine varieties, although perfectly satisfactory results are obtained 
 with such grapes without sulfuring. Sulfuring appeared to injure 
 the flavor even when used for a very short length of time, and it is 
 doubtful whether the improved color compensates for the injury to 
 flavor. 
 
 As noted elsewhere in this report, unprotected screen trays became 
 badly corroded by sulfur fumes and the zinc salts so formed imparted 
 a metallic flavor to the fruit. The use of slat bottom trays would solve 
 this problem. 
 
 The results of our Davis experiments indicate that slightly greater 
 yields of dried product are obtained if the grapes are sulfured before 
 sun-drying or evaporation. Increased yields were obtained in a large 
 
 - 
 
Bulletin 322 THE EVAPORATION OF GRAPES 451 
 
 number of experiments, but were relatively small in amount. Further 
 tests must be made to confirm the results of the past season. The 
 sulfurous acid absorbed by the fruit from the burning sulfur perhaps 
 reduces loss by oxidation during drying and this might account for 
 the increased yields observed. Further tests are necessary on this 
 point. 
 
 Sulfuring is not necessary and is not recommended as a general 
 practise in drying wine grapes. 
 
 (d) EFFECT OF TEMPERATURE ON QUALITY AND RATE OF DRYING 
 
 Theoretically, the rate of drying is directly proportional to the 
 temperature, inversely proportional to the humidity, and proportional 
 to the square root of the air velocity. These principles hold for the 
 evaporation of water from a free surface. 
 
 Tests were first made in the laboratory to determine the effect 
 of temperature on the rate of drying. The air velocity and other 
 conditions were identical in all cases; only the temperature being 
 varied. The following table and curves give the results of the tests 
 made with Tokay grapes. Similar results were obtained with Alicante 
 Bouschet grapes. 
 
 Table 4. — Effect of Temperature on Rate of Drying of Tokay Grapes 
 
 140° ] 
 
 h\-145° F. 
 
 160° F. 
 
 -165° F. 
 
 190° F, 
 
 -200° F. 
 
 Time in 
 hours 
 
 Weight in 
 grams 
 
 Time in 
 hours 
 
 Weight in 
 grams 
 
 Time in 
 hours 
 
 Weight in 
 grams 
 
 
 
 2000 
 
 
 
 2000 
 
 
 
 2000 
 
 6 
 
 980 
 
 4 
 
 1100 
 
 3 
 
 850 
 
 10 
 
 585 
 
 9 
 
 605 
 
 5.5 
 
 565 
 
 16 
 
 520 
 
 14 
 
 440 
 
 7.5 
 
 485 
 
 20 
 
 500 
 
 
 
 
 
 25 
 
 498 
 
 
 
 
 
 29 
 
 480 
 
 
 
 
 
 In large-scale experiments made by one of the authors* dipped 
 Alicante Bouschet grapes were dried in six hours at 190° F., whereas 
 sixteen hours' time was required to dry the same variety of grapes 
 at 160° F. 
 
 The grapes dried at 190° F. in the large-scale tests at Yountville 
 were dried in recirculated air of relatively high humidity. They 
 appeared to be of equal quality in all respects to the grapes of the 
 same variety evaporated at 160° F. Alicante Bouschet grapes dried 
 
 * A. W. Christie, in cooperation with J. W. Pearson and G. B. Ridley in the 
 Pearson evaporator at Yountville. 
 
452 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 in the small laboratory evaporator at 190° F. appeared to be of equal 
 quality to those dried at 145° F. and 165° F., although when the grapes 
 were left in the evaporator for several hours at 190° F. to 200° F. 
 after becoming dry, a noticeable caramelized flavor developed. Tokay 
 grapes developed the caramelized flavor more rapidly than did the 
 Alicante Bouschet and exhibited this flavor to an appreciable degree 
 even when removed from the evaporator as soon as sufficiently dry. 
 The tests indicate, however, that temperatures of 190° F. to 200° F. 
 under certain conditions may be safely used for Alicante Bouschet 
 grapes and probably for other red-wine grapes. Recent analyses of 
 the above lots of dried grapes show that a great deal of sugar was 
 lost by action of heat at 190° F. 
 
 I 
 
 ZJA ^r Z CT Or T ^ M PL R/iT i/ R E 
 
 I 
 
 Q rt F?A rr OIL ntW/rvG 
 
 e 3 /o /%, /+ '6/8 Ao 
 
 Fig. 8. — Curves illustrating the comparative rates of drying of Tokay grapes 
 at three different temperatures. 
 
 (e) EFFECT OF CONSTEUCTION OF TEAYS 
 
 Most of the trays used in our experiments consisted of a wooden 
 frame, 3' X 3', with a wire-screen bottom. Screens of y 2 , % and ^ 
 inch mesh were used. In addition to the screen-bottom trays a few 
 trays were constructed with slat bottoms. The slats were about y 2 
 by % inch in size and were placed about % of an inch apart. The 
 accompanying figure illustrates the construction of these trays. 
 
 The framework of each tray consisted of: 
 
 2 pieces, 36" X 1%" X 1%"; 2 pieces, 33" X %" X %"; 
 
 2 pieces, 36" X %" X 1%"; 1 piece, 33" X %" X 1"; and 
 
 2 pieces, 33" X %" X 1%"; 1 piece, 34" X %" X %"• 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 453 
 
 The 36" X 1%" X 1%" pieces over pieces 33" X %" X iy 2 " 
 formed the sides of the trays. These trays are the standard trays used 
 at Fresno for drying raisins preliminary to cap stemming. It was 
 found that the trays were not deep enough for grape varieties pro- 
 ducing large bunches. Therefore, strips %" X l 1 /^" were nailed to 
 the side strips to increase the height of the sides of each tray suf- 
 ficiently for the bottoms of the trays to clear the bunches of grapes on 
 the tray beneath. This gives a distance of 3 inches between screens, 
 a space sufficient to permit free circulation of air and rapid and even 
 drying. 
 
 Fig. 9. — Photographs of screen bottom and slat bottom trays used in experi- 
 ments at Davis. Trays are 3' X3' in size. 
 
 Several serious objections to screen trays were encountered. The 
 most serious was the tenacity with which the dried grapes adhered to 
 the screen. The time of two or three men was needed to scrape the 
 dried grapes from the trays whenever the evaporator was operated to 
 full capacity. Users of other evaporators experienced the same dif- 
 ficulty, except where the grapes were dried without dipping. The 
 juice from dipped grapes dried to a thick syrup at the point of contact 
 of the berries and screen, thus cementing the fruit firmly to the trays. 
 The vigorous scraping necessary to remove the fruit was severe on 
 the wire screens and wooden frames of the trays; many of the trays 
 became more or less weakened in one season's use on this account. 
 
 Where the grapes were sulfured the sulfurous acid generated by 
 the burning sulfur attacked the zinc coating of the wire screens to 
 such an extent that soluble zinc salts were formed in sufficient quantity 
 to impart a metallic taste to the fruit. 
 
454 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Paraffine was tested as a coating for the trays. It was melted and 
 applied to the screens with a brush. It protected the screen fairly 
 well against corrosion, but caused the dried fruit to adhere to the 
 screen even more tightly than where no paraffine was used. Asphalt 
 and Gilsonite base paints and other special paints and varnishes either 
 became soft and adhered to the fruit in the evaporator or became 
 brittle and chipped off the screen during removal of the dried fruit 
 from the trays. The authors are still searching for a suitable tray 
 coating and have obtained several promising materials. 
 
 The rates of drying for grapes of several varieties on screen and 
 on slat-bottom trays were compared by placing grapes on slat-bottom 
 trays on cars loaded with screen trays containing the same variety of 
 grapes. No difference in the rates of drying could be noticed. It 
 was found, however, that the dried grapes were removed with great 
 ease from the slat-bottom trays, there being practically no tendency 
 to stick. Furthermore, these trays are rigid and retain their shape 
 without sagging. There is, of course, no formation of metallic salts 
 or corrosion of the trays by the action of sulfur fumes. Slat-bottom 
 trays may be constructed at less cost than screen trays. 
 
 Trays with solid wooden bottoms of the type ordinarily used in 
 sun-drying were compared with screen-bottom trays to determine the 
 relative rates of drying on each. This is an important point because 
 many grape growers already possess ordinary field trays and naturally 
 wish to make use of them if they construct an evaporator. A test was 
 first made in a commercial evaporator in which the air-blast rises 
 vertically from a fan. In this evaporator the fruit (apricots) dried 
 only one half as rapidly on the solid wooden bottom trays as on the 
 screen trays. In our small laboratory evaporator, however, the tests 
 were repeated with grapes and the use of a horizontal blast of air; 
 that is, the heated air was blown across the trays. Five different 
 varieties of grapes were tested. The different trays were of exactly 
 the same length, breadth and depth, the only difference being in the 
 construction of the tray bottoms. 
 
 The rate of drying in the case of the Muscat and Tokay grapes 
 was practically a^ rapid on the wooden trays as on the screen trays. 
 Burger grapes dried somewhat more rapidly on screen than on wood, 
 although the difference was not very pronounced. This indicates that 
 the ordinary solid bottom sun-drying trays can be successfully used 
 in an evaporator where a horizontal air blast is employed providing 
 the trays are separated by blocks or cleats to permit an ample flow 
 of air. 
 
Bulletin 322 
 
 THE EVAPORATION OF GRAPES 
 
 455 
 
 (/) COMPARISON OF GRAVITY AND AIR-BLAST BURNERS 
 
 Two furnaces, each consisting of an old boiler shell 6 feet long 
 by 3 feet in diameter connected to approximately 40 feet of 12-inch 
 pipe were installed in the furnace room of the evaporator at Davis. 
 In one of these was placed a medium-size air-blast burner and in the 
 second furnace a large-size gravity burner. Except in very cold 
 weather, it was found possible to maintain the air entering the evapo- 
 rator at 140° F. to 145° F., using either burner alone. When the 
 
 :ffiL 
 
 SECT/ ON Or UNIVERSITY RfiRM DIRROR 
 Fig. 10. — Sketch of dipping- machine used at University Farm evaporator, 1919. 
 
 exhaust air was allowed to escape freely from the tunnel outlet, 
 practically the full capacity of one burner was required to maintain 
 the evaporator above 140° F., but when a large portion of the air 
 was recirculated it was possible to maintain this temperature by using 
 the air-blast burner at one half to two thirds capacity. 
 
 The air-blast burner was somewhat more efficient than the gravity 
 burner for the reason that the latter gave incomplete combustion of 
 the fuel. This fact was indicated by the black smoke which issued 
 from the stack of the gravity burner furnace and by the large accumu- 
 lation of soot in the radiating pipes. It was found necessary to seal 
 the joints of the radiating pipes of this furnace with fire cement to 
 prevent the soot from entering the tunnel with the heated air and 
 causing blackening of the fruit. The air-blast burner on the other 
 
456 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 hand produced no soot; in fact, it was found possible to pass all the 
 products of combustion of this furnace through the drying tunnel 
 without injury to the grapes. 
 
 The gravity burner tended to heat the furnace walls less uniformly 
 than did the air-blast burner. The flame of the latter extended 
 throughout the entire length of the furnace, whereas that of the 
 gravity burner was more localized and most intense immediately 
 above the burner. An air-blast burner has another advantage in that 
 a full flame is obtained immediately on lighting the burner, whereas 
 at least a half hour is required to bring the gravity burner to full 
 capacity. 
 
 In spite of these defects the gravity burner was found to be fairly 
 satisfactory. It could be used successfully in localities where electric 
 power is not available for the operation of an air-blast burner. It is 
 cheap, easily installed, and simple in operation. 
 
 Our results demonstrated that one blast burner is sufficient for an 
 evaporator of this size provided a large proportion of the air is recir- 
 culated. The furnaces were only six feet in length. One furnace 
 ten or twelve feet long would be much more satisfactory because the 
 flame of the air-blast burner often extended beyond the furnace into 
 the radiating pipes. Only 40 feet of radiating pipe was used on each 
 furnace. At least twice this amount should have been installed in 
 order to reduce stack losses of heat to a minimum. By constructing 
 the furnace according to these suggestions and eliminating one furnace 
 it would be possible to greatly reduce the size and cost of the air- 
 heating room. (See revised plans for further details.) 
 
 (g) OOMPAKISON OF DISC AND MULTIVANE FANS 
 
 No direct comparison of these two types of fans was made, but the 
 rate of air flow through a large tunnel equipped with the multivane 
 type of fan was determined and compared with the results of similar 
 readings made upon the University Farm evaporator which was 
 equipped with a disc fan. 
 
 Our drying tunnel was approximately 33 feet long and 6V2 X 7 
 feet in cross section. The rate of air flow over the trays on the last 
 car when the tunnel was filled with loaded cars varied from 100 to 
 350 feet per minute. The average was approximately 220 feet per 
 minute. 
 
 The drying tunnel of an evaporator in Napa County which was 
 used for comparison was approximately 68 feet long and of about 
 the same cross section as our evaporator. In this evaporator a multi- 
 
Bulletin 322 
 
 THE EVAPORATION OP GRAPES 
 
 457 
 
 vane fan was operated at such speed as to deliver 18,000 cubic feet 
 per minute (catalog rating), actual delivery 12,500 cubic feet per 
 minute with loaded tunnel. (The disc fan was rated at 25,000 cubic 
 feet per mnute.) When approximately 60 feet of the larger drying 
 tunnel's length was filled with loaded cars the rate of air flow over 
 the trays on the last car was approximately 420 feet per minute. The 
 multivane fan operated against approximately double the resistance 
 of the disc fan because the loaded tunnel was twice as long. In spite 
 of this greater resistance the multivane fan gave a much greater rate 
 of air flow ; a fact which accounts for the more rapid rate of drying 
 in this evaporator. 
 
 Fig. 11. — Multivane fan on left; disc fan on right. 
 
 These observations were not extensive, but nevertheless clearly 
 indicate the great superiority of the multivane fan over the disc 
 fan. The former is considerably more expensive than the latter but 
 the difference in price is more than compensated for by the advantages 
 of the multivane type. In addition to causing more rapid drying, it 
 permits the use of longer tunnels, and thus makes possible a more 
 complete utilization of the moisture-absorbing power of the air. 
 
 It is our opinion that the ideal ventilating system for an evaporator 
 would be a multivane exhaust fan so arranged in relation to the air- 
 heating system and air-return flue that the heated air may be drawn 
 by the fan over the trays by suction, and any desired proportion of 
 this exhaust air returned to the furnace room to be mixed with fresh 
 air and recirculated. 
 
458 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 This would combine the advantages of recirculation and humidity 
 control with that of an exhaust fan of the multivane type. 
 
 The planing mill exhaust-type of fan, which is a more powerful 
 type than the multivane, has been used successfully by a commercial 
 evaporating company. This type of fan requires for operation con- 
 siderably more power than the multivane fan of the same rating. It 
 remains to be seen whether the planing mill exhauster will demonstrate 
 advantages which will compensate for this greater cost for power. 
 
 (ft) EXHAUST VERSUS POSITIVE BLAST FAN 
 
 The evaporator at Davis was equipped with a 60-inch disc fan 
 at the furnace end of the tunnel. This was connected to a 7% h.p. 
 electric motor and was operated at such speed as to deliver theo- 
 retically 25,000 cubic feet of air per minute (catalog rating). At the 
 outlet end of the tunnel was located a 54-inch disc fan, which could 
 be used as a suction or exhaust fan at such speed that 25,000 cubic 
 feet of air per minute should theoretically (catalog rating) have been 
 drawn through the tunnel. As a matter of fact the actual amount of 
 air delivered varied from about 10,000 cubic feet to 15,000 cubic feet 
 per minute with each fan. 
 
 The evaporator was operated experimentally for a period of sev- 
 eral days with the suction fan or the blast fan only. The conditions 
 in the experiments being similar in other respects, the rate of drying 
 of Tokay grapes was used as a basis for comparison. The following 
 table summarizes the more important results obtained. 
 
 Table 5. — Comparison of Suction and Positive Blast Fans 
 
 1. Fuel consumption, gallons per hour .... 
 
 2. Average temperature of air at furnace 
 
 end of tunnel 
 
 3. Average temperature of outside air .... 
 
 4. Average increase of temperature 
 
 5. Humidity at furnace end of tunnel .... 
 
 6. Time to dry tokay grapes, hours 
 
 7. Average rate of air flow at end of tun- 
 
 nel, feet per minute 180 198 
 
 8. Eelative efficiency based on time of 
 
 drying and fuel consumption, test 
 
 II taken as 100 60.22% 100% 
 
 •sitive blast fan 
 
 I 
 
 Suction fan 
 II 
 
 7.50 
 
 8.8 
 
 133.4° F. 
 
 138.02° F. 
 
 67.7° F. 
 
 67.3° F. 
 
 65.7° F. 
 
 70.72° F. 
 
 3% 
 
 7% 
 
 73 
 
 37.5 
 
Bulletin 322 TIIE EVAPORATION OF GRAPES 459 
 
 The data given in the above table indicate that the suction fan is 
 much more satisfactory and efficient than the positive blast fan. The 
 slightly higher temperature of the air and the slightly greater rate 
 of air flow probably accounts for the more rapid rate of drying with 
 the suction fan. 
 
 In addition to more rapid drying, the suction fan appeared to 
 cause the grapes to dry more evenly. However, too few observations 
 were made upon this point to determine conclusively whether the 
 difference was appreciable. 
 
 From the results of the above tests it would appear that evapora- 
 tors equipped with the disc type of fan should make use of this fan 
 as a suction fan rather than as a positive blower. It can not be stated 
 whether the same relation holds true for other types of fans such as 
 the multivane and mill exhaust fans. 
 
 (i) EECIRCTJLATION OF AIE 
 
 The evaporator was of such construction that any proportion of 
 the air, after its passage through the tunnel, could be returned to 
 the furnace room to be reheated and recirculated. A description of 
 the recirculation system will be found in the plans and specifications. 
 
 In order to determine the relative rates of drying and relative fuel 
 efficiency three tests were made. In one of these tests, the positive 
 blast fan was used with outlet of tunnel completely opened and return 
 air flue closed so that none of the air was recirculated. In another 
 test, the tunnel outlet was closed to such a point that the air outlet 
 was approximately three inches wide and seven feet long. The return 
 air flue was opened as completely as possible, permitting a large pro- 
 portion of the air (approximately 75%) to recirculate. In the third 
 test, both the tunnel outlet and the return flue were left completely 
 open. This permitted the recirculation of a smaller proportion of 
 the air than in the second test. A great many observations on the 
 rate of air flow, humidity, and rates of drying were made, but only 
 the more essential results are given in table 6 on page 460. 
 
 In addition to the data given on rates of drying, it may be stated 
 that Carignane grapes were dried in the first test in 20 hours and the 
 maximum time required for any variety in this test was 33 hours. In 
 the second test, the minimum time of drying was 46 hours and the 
 maximum 73 hours; while in the third, 58 and 68 hours' time, respec- 
 tively, were required. 
 
 Of the conditions existing in the evaporator during these three 
 tests the temperature variation was the factor which would affect the 
 
460 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 rates of drying to the greatest degree. The fact that it was possible 
 to maintain a higher temperature with the same fuel consumption 
 during recirculation accounts for the greater efficiency of this method. 
 The figures would indicate that the saving in fuel by use of recircu- 
 lation was approximately 41%, basing this calculation upon a com- 
 parison of the first and second tests. 
 
 Table 6. — Effect of Recirculation on Fuel Efficiency and Eate of Drying 
 
 Recirculation, No Recirculation. 
 
 Tunnel outlet recirculation. Tunnel outlet 
 
 nearly closed. Blast fan. completely open. 
 
 Observation I II III 
 
 1. Average fuel consumption 
 
 per hour, gallons 7.57 7.50 6 
 
 2. Average temperature of air 
 
 at furnace end of tunnel 141.1° F. 133.4° F. 127.4° F. 
 
 3. Average temperature of out- 
 
 side air 65.5° F. 67.7° F. 71.1° F. 
 
 4. Average increase in tem- 
 
 perature of air 75.6° F. 65.7° F. 56.3° F. 
 
 5. Volume of air passing 
 
 through tunnel, cubic feet 
 per minute (approxi- 
 mate) 12,800 12,800 12,800 
 
 6. Humidity of air at furnace 
 
 end of tunnel 10% 3% 7% 
 
 7. Average time required to dry 
 
 grapes of same lot, hours 27.5 47 58.6 
 
 8. Fuel required to dry six tons 
 
 of grapes, gallons 208 352 351 
 
 9. Relative efficiency based on 
 
 time of drying and fuel 
 consumption (test I 
 taken as 100) 3 00% 59.14% 59.30% 
 
 Small-scale tests in the laboratory evaporator confirmed these 
 observations. It was found that the burning of only about one half 
 as much gas was necessary to maintain a given temperature when 
 most of the air was recirculated. In these experiments it was prac- 
 tically impossible to over-dry grapes when most of the air was re- 
 circulated. The grapes dried to a certain moisture content and 
 remained at that degree of dryness even when the evaporator was 
 operated for a number of hours after this condition was reached. 
 This indicates that it is possible to control the moisture content of 
 the finished product by accurate control of the proportion of recircu- 
 lated air. The importance of this fact can not be overemphasized, 
 because it is very difficult to judge by observation of the grapes in 
 the evaporator, whether they are sufficiently dry. The tendency of 
 the beginner is to over-dry, which results in a low yield of inferior 
 fruit. 
 
Bulletin 322 TH e EVAPORATION OP GRAPES 461 
 
 These results were further confirmed by experiments made with a 
 large commercial evaporator at Yountville.* Similar observations 
 have been made by T. I. Casey and other manufacturers and users 
 of evaporators equipped with the recirculation system. 
 
 A third advantage of recirculation claimed by Mr. Paul F. Nichols 
 of the United States Department of Agriculture is that higher tem- 
 peratures of drying may be used without injury to the fruit, if 
 recirculation of the air is employed. Our own preliminary experi- 
 ments indicate this to be true, but our investigations on this point have 
 not been extensive enough to warrant definite conclusions. 
 
 We wish, therefore, to repeat a statement made earlier in this pub- 
 lication, viz., that the prospective purchaser or builder make certain 
 that the evaporator shall be so constructed that any proportion of 
 the air used in drying may be recirculated. 
 
 (j) DIRECT USE OF GASES OF COMBUSTION IN DRYING 
 
 In most evaporators a large amount of heat is lost in the gases 
 leaving the smoke stack. It is evident that this loss could be elimin- 
 ated if these gases may be passed through the evaporator after mixing 
 with a sufficient quantity of outside air to give the desired tempera- 
 ture. This method has been used for many years in the drying of 
 garbage and more recently in drying kelp (sea weed). Until recently, 
 it had not been applied to the drying of fruits, because of the difficulty 
 in eliminating all soot, smoke, and disagreeable odors in the burning 
 of the fuels heretofore in use. It has been found during the past two 
 or three years, however, that the products of combustion of natural 
 gas may be used directly in the drying of fruits without injury to 
 the quality of the dried product. At least three different types of 
 evaporators are now successfully using this fuel in the above way. 
 
 More recently, improvements in the design of air-blast burners 
 using stove distillate, have made possible such complete combustion 
 of this fuel that the gases of combustion do not affect the flavor, odor, 
 or color of the fruit. In one evaporator, in which this method has 
 been highly developed, the fuel is burned in a long arched firebrick 
 furnace in which is used a special form of air-blast burner. The 
 furnace opens directly into the flue leading to the fan. This flue is 
 fitted with a cold-air intake. By regulation of the size of this intake 
 the mixed air and gases of combustion are given the desired tempera- 
 ture before they reach the fan. The furnace gases may during the 
 
 * These tests were made in the Pearson evaporator in cooperation with Messrs. 
 Pearson and Ridley. 
 
462 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 time necessary to heat the furnace be diverted into a smoke stack. 
 This is necessary because a cold furnace prevents complete combustion. 
 
 It was found that grapes and. apples could be dried in this type 
 of evaporator without injury to quality from soot or fumes. The 
 efficiency of this method in heating air is remarkable, tests showing 
 that over 98% of the heat liberated in the combustion of the fuel was 
 applied in heating the air.* 
 
 The furnace at the University Farm was not designed for the 
 direct use of the gases of combustion, but in order to obtain a rough 
 comparison of the relative efficiency of direct and indirect heating 
 of the air, the furnace equipped with the air-blast burner was so 
 arranged as to permit the gases of combustion to escape into the 
 furnace room and to be drawn through the evaporator by a suction 
 fan. 
 
 Tokay grapes were dried in 20 hours. The quality of the dried 
 product was equal to that of the product dried by air heated in the 
 usual way. A comparison of the temperatures attained, volume of air 
 heated and fuel consumption in the two methods are shown in the 
 following table. 
 
 Table 7. — Effect on Efficiency of Utilization of Fuel of Heating Air by 
 Mixing with Gases of Combustion 
 
 Direct use of 
 gases of 
 Radiated heat combustion 
 
 Observations I II 
 
 1. Gallons of fuel per hour 8.8 6.7 
 
 2. Average temperature of outside air.... 69° F. 67° F. 
 
 3. Temperature of heated air .' 138.02° F. 145.2° F. 
 
 4. Eise in temperature 69° F. 88° F. 
 
 5. Volume of air per minute entering 
 
 furnace roomf 12,800 15,700 
 
 6. Relative efficiency of use of fuel, using 
 
 volume of air heated, temperature 
 rise and fuel consumption as basis 
 for computation (test II taken as 
 100) 67.5% 100% 
 
 When the gases of combustion were used it was found possible to 
 increase the temperature of the air entering the tunnel to 190° F. 
 without difficulty. Temperatures of 165° P. to 175° F. were easily 
 maintained. 
 
 * Calculation made by Mr. G. B. Ridley from calorific value of the fuel, and 
 volume of air heated. 
 
 t Only two cars were in the tunnel during the test on use of . gases of com- 
 bustion. This gave less resistance to air than in first test and accounts for greater 
 air flow and more rapid rate of drying. 
 
Bulletin 322 THE EVAPORATION OF GRAPES 463 
 
 The data given in the above table are the results of one test only ; 
 nevertheless, a much greater efficiency for the direct heating method 
 is indicated. Further investigations will be made upon this point 
 during the coming season. 
 
 Crude oil is a much cheaper fuel than stove distillate, but the gases 
 of combustion from the former have not been used in drying because 
 of the greater tendency for the formation of soot and smoke. Crude 
 oil is, however, used very commonly in furnaces which heat the air 
 by radiation. The question arises whether the greater efficiency of 
 the use of the gases of combination from the burning of stove distillate 
 will more than compensate for the greater cost of this fuel, as com- 
 pared to the cost of crude oil which is used only in furnaces heating 
 the air by radiation. We do not have sufficient data to answer this 
 question ; but it is a point which the builder of an evaporator must 
 carefully consider. 
 
 (fc) MOISTURE CONTENT OF EVAPORATED GEAPES 
 
 The yield of dried product varies in proportion to its moisture 
 content; this fact makes it important for the operator to know the 
 maximum percentage of water evaporated grapes may contain with- 
 out becoming moldy or undergoing fermentation. 
 
 Sixty-one samples of dried grapes, including several varieties from 
 the University Farm and from commercial evaporators, and eighteen 
 samples dried in the laboratory were analyzed. The average moisture 
 content of the University Farm and commercially dried samples was 
 13.83% ; the minimum was 8.8%, and the maximum, 44.10%. This 
 last sample had fermented and the very high moisture content indi- 
 cated represents to a large extent loss from alcohol formed from the 
 grape sugar. The average moisture content of the samples dried in 
 the laboratory was 12.54%. 
 
 A commercial sample containing 30% moisture had undergone 
 fermentation three months after the date of drying, although at one 
 month the sample was free from any evidence of fermentation. Two 
 samples from the University Farm containing 29.3% and 33.5% 
 moisture, respectively, have not fermented or become moldy, but both 
 lots had been heavily sulfured before drying, which probably accounts 
 for their resistance to spoilage. Several lots which had not been sul- 
 fured and which contained 25% to 25.4% moisture have given no 
 evidence of decomposition after four months' storage in sealed con- 
 tainers. A relatively larger number of samples containing between 
 20% and 25% moisture have kept perfectly. Therefore, it would 
 
464 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 appear to be safe to state that grapes dried to 24% or 25% moisture 
 will not spoil and that 20% moisture content will certainly under 
 Californian conditions not permit molding or fermentation. 
 
 The trade prefers dried grapes that have been stemmed and packed 
 in fifty-pound boxes. Stemming can not be satisfactorily accom- 
 plished unless the grapes are reduced to approximately 10% moisture. 
 This would necessitate a reduction in possible yield of 10% to 15% 
 through the extra degree of drying necessary to permit stemming. 
 However, in the commercial packing of Muscat raisins the moisture 
 which is removed from the raisins in order to make stemming possible 
 is returned by processing in hot water before the raisins are passed 
 through the seeding machine; the final water content of the packed 
 raisins being approximately 16% to 20%. Commercial practice has 
 demonstrated that such fruit does not mold or ferment. 
 
 Therefore, it should be possible to return to the stemmed evaporated 
 raisins enough water to give in the finished product that amount of 
 moisture which causes the raisins to be of the most desirable texture ; 
 that is, about 20%. 
 
 As the dried grapes come from the evaporator they are not of a 
 uniform moisture content; some bunches will be over-dry, others too 
 wet. It is desirable to allow the dried product to stand in sweat boxes 
 or bins for a number of days (probably at least two weeks) to permit 
 equalization of moisture. This will be particularly necessary for 
 stemmed dried grapes to which water has been added. Because of 
 the small size of the individual berries, evaporated grapes equalize in 
 water content more rapidly than do the larger dried fruits. It was 
 observed that partially dried grapes from which juice could still be 
 pressed easily gave up this excess moisture to the drier grapes in the 
 sweat box before fermentation or molding could take place, provided 
 the average moisture content of the whole lot was not too high. 
 
 The only method in common use which has proved accurate for 
 estimating the moisture content of dried grapes consists in drying a 
 weighed average sample of the finely ground raisins in a vacuum oven. 
 A temperature of 90° C. (196° F.) may be used in this determination, 
 provided the sample is not heated longer than necessary to remove 
 all the water. Drying in an oven open to the air gave excessively high 
 results at all temperatures used because of the loss in weight through 
 oxidation of the fruit sugars. Preliminary experiments indicate that 
 it is possible to estimate the moisture by a simple method based upon 
 the distillation of the sample with a liquid immiscible with water. 
 This method is sufficiently accurate to be very useful to operators of 
 evaporators for controlling the moisture content of the dried product. 
 
Bulletin 322 THE evaporation OP grapes 465 
 
 (I) THE DETERMINATION OF HUMIDITY 
 
 The efficiency of an evaporator depends largely npon the degree 
 of saturation with moisture of the exhaust air. If the humidities of 
 the hot air entering the drying tunnel and of the air leaving the 
 tunnel are measured, the amount of moisture absorbed from the fruit 
 may be easily calculated and the efficiency of the evaporator deter- 
 mined. Humidity may be determined by reading the temperature 
 of wet and dry bulb thermometers placed at the desired points and 
 by use of the following table. Explicit directions for use of ther- 
 mometers and table are given in the discussion immediately following 
 the table. 
 
 Two accurate Fahrenheit thermometers (of the variety known as 
 "chemical thermometers") are the only instruments needed. Ordi- 
 nary dairy thermometers reading to 180° F. or 225° F. may be used 
 if chemical thermometers are not easily obtainable. Most drug stores 
 carry thermometers of both types or can obtain them on short notice. 
 
 Special instruments may be used instead of the ordinary ther- 
 mometers. One known as a "sling psychrometer" which consists of 
 two thermometers mounted side by side on a narrow frame is very 
 convenient and accurate. Another instrument is so constructed that 
 humidity is read directly by means of a chart and pointer mounted 
 upon the device itself. The Taylor Instrument Company's Hygrodeik 
 is the most common form of this latter instrument. Its only fault is 
 that it may be used only for temperatures up to 120° F. 
 
 Around the mercury bulb of one of the thermometers wrap a small 
 piece of cheese cloth of five thicknesses and extending about one-half 
 inch above the bulb. Be sure all of the bulb is covered with the cloth. 
 Tie the cloth with thread or fasten with small rubber band. 
 
 Dip the thermometer with the cloth-covered bulb in water. Hang 
 it beside the other .plain thermometer at the point where the test is to 
 be made. Watch the two thermometer columns closely. As soon as 
 they remain at constant temperatures for about one minute read both 
 carefully. It will usually require three to five minutes for the ther- 
 mometers to come to constant temperature. Do not wait too long as 
 the wet-bulb cloth will then dry out and the temperature will rise too 
 high. This point is important. On the other hand, do not take this 
 reading too soon as it will then be too low. A little experience will 
 render readings fairly accurate. Now subtract the temperature of 
 the wet bulb from that of the dry bulb. In the extreme left column 
 of the table find the temperature nearest that of the dry bulb. In the 
 
466 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Table 8. — Belation of Humidity to Difference in Temperature of Wet and Dry Bulb 
 
 Thermometers 
 
 (After The Foxboro Company, Incorporated, Foxboro, Massachusetts, U. S. A., catalogue 
 101-1, page 9.) 
 
 Dry 
 Bulb 
 
 Difference Between Readings of Wet and Dry Bulbs in Degrees Fahrenheit 
 
 Dry! 
 Bulb 
 
 Deg. 
 F. 
 
 1 
 95 
 
 2 
 
 90 
 
 3 
 86 
 
 4 
 
 81 
 
 5 
 
 77 
 
 6 
 
 72 
 
 7 
 
 6S 
 
 8 
 64 
 
 9 
 59 
 
 10 
 
 55 
 
 11 
 
 51 
 
 12 
 
 48 
 
 13 
 
 44 
 
 14 
 
 40 
 
 15 
 36 
 
 16 
 
 33 
 
 17 
 
 29 
 
 18 
 
 35 
 
 19 
 
 22 
 
 20 
 
 19 
 
 22 
 
 12 
 
 24 
 
 6 
 
 26 
 
 
 
 28 
 
 
 30 
 
 32 
 
 34 
 
 36 
 
 38 
 
 40 
 
 45 
 
 50 
 
 55 
 
 60 
 
 65 
 
 70 
 
 Deg. 
 F. 
 
 70 
 
 70 
 
 75 
 
 96 
 
 91 
 
 86 
 
 S2 
 
 78 
 
 74 
 
 70 
 
 66 
 
 62 
 
 58 
 
 54 
 
 51 
 
 47 
 
 44 
 
 40 
 
 37 
 
 34 
 
 30 
 
 27 
 
 24 
 
 18 
 
 12 
 
 7 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 75 
 
 80 
 
 96 
 
 91 
 
 87 
 
 S3 
 
 79 
 
 75 
 
 72 
 
 68 
 
 64 
 
 61 
 
 57 
 
 54 
 
 50 
 
 47 
 
 44 
 
 41 
 
 38 
 
 35 
 
 32 
 
 29 
 
 23 
 
 IS 
 
 12 
 
 7 
 
 3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 80 
 
 85 
 
 96 
 
 92 
 
 88 
 
 84 
 
 SO 
 
 76 
 
 73 
 
 70 
 
 66 
 
 63 
 
 59 
 
 56 
 
 53 
 
 50 
 
 47 
 
 44 
 
 41 
 
 38 
 
 35 
 
 32 
 
 27 
 
 22 
 
 17 
 
 13 
 
 8 
 
 4 
 
 
 
 
 
 
 
 
 
 
 
 
 
 85 
 
 90 
 
 96 
 
 92 
 
 89 
 
 85 
 
 SI 
 
 78 
 
 74 
 
 71 
 
 68 
 
 65 
 
 61 
 
 58 
 
 55 
 
 52 
 
 49 
 
 47 
 
 44 
 
 U 
 
 39 
 
 36 
 
 31 
 
 26 
 
 22 
 
 17 
 
 13 
 
 9 
 
 5 
 
 1 
 
 
 
 
 
 
 
 
 
 
 90 
 
 95 
 
 96 
 
 93 
 
 89 
 
 85 
 
 S2 
 
 79 
 
 75 
 
 72 
 
 69 
 
 66 
 
 63 
 
 60 
 
 57 
 
 54 
 
 52 
 
 49 
 
 46 
 
 43 
 
 42 
 
 38 
 
 34 
 
 30 
 
 25 
 
 21 
 
 17 
 
 13 
 
 9 
 
 6 
 
 2 
 
 
 
 
 
 
 
 
 
 95 
 
 100 
 
 96 
 
 93 
 
 89 
 
 86 
 
 S3 
 
 80 
 
 77 
 
 73 
 
 70 
 
 68 
 
 65 
 
 62 
 
 59 
 
 56 
 
 54 
 
 51 
 
 49 
 
 46 
 
 44 
 
 41 
 
 37 
 
 33 
 
 28 
 
 24 
 
 21 
 
 17 
 
 13 
 
 10 
 
 7 
 
 4 
 
 
 
 
 
 
 
 100 
 
 105 
 
 97 
 
 93 
 
 90 
 
 87 
 
 83 
 
 80 
 
 77 
 
 74 
 
 72 
 
 69 
 
 66 
 
 63 
 
 60 
 
 58 
 
 55 
 
 53 
 
 50 
 
 48 
 
 46 
 
 44 
 
 40 
 
 36 
 
 32 
 
 28 
 
 23 
 
 20 
 
 16 
 
 13 
 
 11 
 
 8 
 
 
 
 
 
 
 
 
 105 
 
 110 
 
 97 
 
 93 
 
 90 
 
 87 
 
 84 
 
 81 
 
 7S 
 
 75 
 
 73 
 
 70 
 
 67 
 
 65 
 
 62 
 
 60 
 
 57 
 
 55 
 
 52 
 
 50 
 
 48 
 
 46 
 
 42 
 
 38 
 
 34 
 
 30 
 
 26 
 
 23 
 
 20 
 
 17 
 
 14 
 
 11 
 
 4 
 
 
 
 
 
 
 
 110 
 
 115 
 
 97 
 
 94 
 
 91 
 
 88 
 
 85 
 
 82 
 
 79 
 
 76 
 
 74 
 
 71 
 
 68 
 
 66 
 
 63 
 
 61 
 
 58 
 
 57 
 
 54 
 
 52 
 
 50 
 
 48 
 
 43 
 
 40 
 
 36 
 
 32 
 
 28 
 
 26 
 
 22 
 
 20 
 
 16 
 
 14 
 
 7 
 
 2 
 
 
 
 
 
 115 
 
 120 
 
 97 
 
 94 
 
 91 
 
 88 
 
 85 
 
 82 
 
 80 
 
 77 
 
 74 
 
 72 
 
 69 
 
 67 
 
 65 
 
 62 
 
 60 
 
 58 
 
 55 
 
 53 
 
 51 
 
 49 
 
 45 
 
 41 
 
 38 
 
 34 
 
 31 
 
 28 
 
 25 
 
 22 
 
 19 
 
 17 
 
 10 
 
 5 
 
 
 
 
 
 
 120 
 
 125 
 
 97 
 
 94 
 
 91 
 
 88 
 
 85 
 
 S3 
 
 SO 
 
 78 
 
 75 
 
 73 
 
 70 
 
 68 
 
 66 
 
 63 
 
 61 
 
 59 
 
 57 
 
 54 
 
 52 
 
 50 
 
 47 
 
 43 
 
 40 
 
 36 
 
 33 
 
 30 
 
 27 
 
 24 
 
 22 
 
 19 
 
 13 
 
 7 
 
 2 
 
 
 
 
 
 125 
 
 130 
 
 97 
 
 94 
 
 91 
 
 89 
 
 86 
 
 S3 
 
 81 
 
 78 
 
 76 
 
 73 
 
 71 
 
 69 
 
 67 
 
 64 
 
 62 
 
 60 
 
 58 
 
 56 
 
 54 
 
 52 
 
 48 
 
 45 
 
 41 
 
 38 
 
 35 
 
 32 
 
 29 
 
 26 
 
 24 
 
 21 
 
 15 
 
 10 
 
 6 
 
 1 
 
 
 
 130 
 
 135 
 
 97 
 
 94 
 
 92 
 
 89 
 
 86 
 
 84 
 
 81 
 
 79 
 
 76 
 
 74 
 
 72 
 
 69 
 
 67 
 
 65 
 
 63 
 
 61 
 
 59 
 
 57 
 
 55 
 
 53 
 
 50 
 
 46 
 
 43 
 
 40 
 
 36 
 
 34 
 
 30 
 
 2S 
 
 26 
 
 23 
 
 18 
 
 12 
 
 8 
 
 3 
 
 
 
 
 135 
 
 140 
 
 97 
 
 95 
 
 92 
 
 89 
 
 87 
 
 84 
 
 82 
 
 79 
 
 77 
 
 75 
 
 73 
 
 70 
 
 68 
 
 66 
 
 64 
 
 62 
 
 60 
 
 5S 
 
 56 
 
 54 
 
 51 
 
 47 
 
 44 
 
 41 
 
 38 
 
 35 
 
 32 
 
 30 
 
 27 
 
 25 
 
 19 
 
 14 
 
 10 
 
 5 
 
 2 
 
 
 140 
 
 145 
 
 98 
 
 95 
 
 93 
 
 90 
 
 87 
 
 84 
 
 82 
 
 80 
 
 78 
 
 75 
 
 73 
 
 71 
 
 69 
 
 67 
 
 65 
 
 63 
 
 61 
 
 59 
 
 57 
 
 55 
 
 52 
 
 4S 
 
 45 
 
 42 
 
 39 
 
 36 
 
 34 
 
 31 
 
 29 
 
 27 
 
 21 
 
 16 
 
 12 
 
 7 
 
 4 
 
 
 
 145 
 
 150 
 
 98 
 
 95 
 
 93 
 
 90 
 
 87 
 
 85 
 
 82 
 
 80 
 
 78 
 
 76 
 
 73 
 
 71 
 
 70 
 
 68 
 
 65 
 
 64 
 
 62 
 
 60 
 
 5S 
 
 56 
 
 53 
 
 49 
 
 46 
 
 43 
 
 41 
 
 38 
 
 35 
 
 33 
 
 30 
 
 28 
 
 23 
 
 IS 
 
 13 
 
 9 
 
 5 
 
 2 
 
 150 
 
 155 
 
 98 
 
 95 
 
 93 
 
 90 
 
 87 
 
 85 
 
 83 
 
 81 
 
 79 
 
 76 
 
 74 
 
 72 
 
 70 
 
 68 
 
 66 
 
 64 
 
 63 
 
 61 
 
 59 
 
 57 
 
 54 
 
 50 
 
 47 
 
 44 
 
 42 
 
 39 
 
 37 
 
 34 
 
 32 
 
 30 
 
 24 
 
 19 
 
 15 
 
 11 
 
 7 
 
 4 
 
 155 
 
 160 
 
 98 
 
 95 
 
 93 
 
 90 
 
 88 
 
 85 
 
 S3 
 
 81 
 
 79 
 
 77 
 
 75 
 
 73 
 
 71 
 
 69 
 
 67 
 
 65 
 
 63 
 
 62 
 
 60 
 
 58 
 
 -)5 
 
 51 
 
 48 
 
 46 
 
 43 
 
 40 
 
 38 
 
 35 
 
 33 
 
 31 
 
 25 
 
 21 
 
 16 
 
 12 
 
 9 
 
 6 
 
 160 
 
 165 
 
 98 
 
 95 
 
 93 
 
 91 
 
 88 
 
 86 
 
 84 
 
 82 
 
 SO 
 
 78 
 
 75 
 
 73 
 
 72 
 
 70 
 
 68 
 
 66 
 
 64 
 
 62 
 
 61 
 
 59 
 
 56 
 
 52 
 
 49 
 
 47 
 
 44 
 
 41 
 
 39 
 
 37 
 
 34 
 
 32 
 
 27 
 
 22 
 
 IS 
 
 14 
 
 10 
 
 7 
 
 165 
 
 170 
 
 98 
 
 96 
 
 94 
 
 91 
 
 89 
 
 86 
 
 84 
 
 82 
 
 80 
 
 78 
 
 76 
 
 74 
 
 72 
 
 70 
 
 69 
 
 67 
 
 65 
 
 63 
 
 62 
 
 60 
 
 57 
 
 53 
 
 50 
 
 48 
 
 45 
 
 42 
 
 40 
 
 38 
 
 35 
 
 33 
 
 2S 
 
 23 
 
 19 
 
 15 
 
 12 
 
 9 
 
 170 
 
 175 
 
 98 
 
 96 
 
 94 
 
 91 
 
 89 
 
 86 
 
 84 
 
 82 
 
 81 
 
 79 
 
 76 
 
 74 
 
 73 
 
 71 
 
 69 
 
 67 
 
 66 
 
 64 
 
 62 
 
 61 
 
 58 
 
 54 
 
 51 
 
 49 
 
 46 
 
 43 
 
 41 
 
 39 
 
 36 
 
 34 
 
 29 
 
 25 
 
 20 
 
 17 
 
 13 
 
 10 
 
 175 
 
 180 
 
 98 
 
 96 
 
 91 
 
 92 
 
 89 
 
 87 
 
 85 
 
 83 
 
 81 
 
 79 
 
 77 
 
 75 
 
 73 
 
 72 
 
 70 
 
 68 
 
 66 
 
 64 
 
 63 
 
 61 
 
 58 
 
 55 
 
 52 
 
 50 
 
 47 
 
 44 
 
 42 
 
 40 
 
 37 
 
 35 
 
 30 
 
 26 
 
 21 
 
 IS 
 
 14 
 
 12 
 
 180 
 
 185 
 
 98 
 
 96 
 
 94 
 
 92 
 
 89 
 
 87 
 
 85 
 
 83 
 
 81 
 
 80 
 
 77 
 
 7li 
 
 74 
 
 72 
 
 70 
 
 69 
 
 67 
 
 65 
 
 64 
 
 62 
 
 59 
 
 56 
 
 53 
 
 50 
 
 48 
 
 45 
 
 43 
 
 41 
 
 38 
 
 36 
 
 31 
 
 27 
 
 22 
 
 19 
 
 16 
 
 13 
 
 185 
 
 190 
 
 98 
 
 96 
 
 91 
 
 92 
 
 90 
 
 87 
 
 85 
 
 83 
 
 82 
 
 so 
 
 78 
 
 76 
 
 74 
 
 73 
 
 71 
 
 69 
 
 68 
 
 66 
 
 64 
 
 63 
 
 60 
 
 57 
 
 54 
 
 51 
 
 49 
 
 40 
 
 44 
 
 42 
 
 39 
 
 37 
 
 32 
 
 2S 
 
 24 
 
 20 
 
 17 
 
 14 
 
 190 
 
 topmost horizontal row of the table find the difference in temperature 
 nearest that of difference in temperature between wet and dry-bulb 
 thermometers. Follow down the vertical column directly beneath this 
 difference in temperature until this vertical column cuts the horizontal 
 row opposite the dry-bulb thermometer temperature. The figure at 
 
Bulletin 322 THE EVAPORATION OF GRAPES 467 
 
 this point of intersection is the relative humidity. An example will 
 make this explanation clearer: 
 
 Dry-bulb thermometer, 130° F. ; wet-bulb thermometer, 103° F. ; 
 difference, 27° F. 
 
 Find in the row at head of table, 28° F. and follow down this 
 column until the horizontal row to the right of 130° F. is met. At 
 this point will be found 38, the per cent relative humidity. 
 
 To determine the increase in humidity of air passing through the 
 evaporator determine the relative humidity of the hot air entering 
 the evaporator and that of the exhaust air. Calculate both to the 
 same temperature by use of the fact that each 27° F. drop in tempera- 
 ture doubles the relative humidity. The increase in humidity can then 
 be calculated. 
 
 (m) MEASUREMENT OF AIR VELOCITY 
 
 The rate of air flow through the evaporator and especially over 
 the trays determines the rate of drying. An instrument known as 
 an anemometer, which consists of a small disc fan made up of small 
 vanes attached to a pinion connected to several dials, is used to meas- 
 ure the velocity of air currents. It is placed with the revolving vanes 
 facing the air current. The "hundreds" dial is read. The clutch 
 is released and the instrument allowed to run for exactly one minute 
 and the dials read again. The difference between first and second 
 reading of "hundreds" dial gives the velocity of the air in hundreds 
 of feet per minute, , The velocity should be in a horizontal blast 
 evaporator at least 300 feet per minute over the trays at the exhaust 
 end of the tunnel. It should be possible to reach 500 feet per minute 
 at this point if the evaporator has been properly designed and built. 
 
 Anemometers may be had from chemical supply houses or from 
 dealers in heating and ventilating equipment. The one used by the 
 University cost twenty-five dollars. The Pitot tube is an instrument 
 used to measure static pressure in the drying tunnel and is a useful 
 check for the anemometer. 
 
 O) EXPERIMENTS ON STEMMING, SEEDING AND PACKING 
 
 In order that evaporated grapes may be stemmed successfully 
 they must be dried to a moisture content of about 10 per cent or less 
 and must be transferred to the stemming machine within a short time 
 (a few hours) after the grapes emerge from the evaporator. They are 
 at this time very dry on the surface and for a short distance into the 
 
468 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 flesh, a condition which gives sufficient rigidity to the berries to permit 
 stemming. After standing over night the moisture near the center of 
 the raisins diffuses toward the surface and moisture is absorbed from 
 the air, causing them to become so soft and pliable that stemming is 
 difficult. The stems of freshly dried grapes are dry and brittle but 
 after a few hours ' standing become wiry and difficult to remove in the 
 stemmer. 
 
 A test was made at a commercial evaporator to determine the loss 
 in weight during stemming. Two hundred and eighty pounds of over- 
 dried Alicante Bouschet grapes were passed through a cleaned stem- 
 ming machine. Stemming was very satisfactory, but few grapes being 
 lost with the stems. The weight of the stems removed was 5.7 per cent. 
 The raisins were not passed through a cap stemmer although many of 
 the cap stems were removed. These grapes had been gathered in such 
 a manner that pieces of cane four to six inches long were left on many 
 of the bunches. This would probably cause the loss in weight during 
 stemming to be higher than the average for grapes picked in the usual 
 manner and this figure should therefore be a conservative one for the 
 calculation of loss due to stemming dried wine grapes under average 
 conditions. 
 
 Through the cooperation of L. R. Payne of the California Asso- 
 ciated Raisin Company of Fresno stemming and seeding tests were 
 made at the Fresno plant of the above company upon small lots of 
 dried Petite Sirah, Semillon, and Muscat grapes. The following table 
 contains the results of Mr. Payne's tests. Because the lots were so 
 small the results on losses during stemming and seeding are exces- 
 sively high, but are still of value for comparison with losses in stem- 
 ming and seeding Muscat raisins under the same conditions. The 
 results given below do not take into account the water returned to the 
 fruit before seeding. 
 
 Table 9. — Losses During Stemming and Seeding Evaporated Grapes. 
 
 Muscat, 
 
 Observations per cent 
 
 1. Stemmer loss 13.69 
 
 2. Drier loss 2.4 
 
 3. Loss in seeding 10.46 
 
 4. Total loss in stemming 
 
 and seeding 24.05 
 
 Semillon 
 
 (white wine 
 
 grapes), 
 
 per cent 
 
 Petite Sirah 
 (red wine 
 grapes), 
 per cent 
 
 Sultanina 
 
 (Thompson 
 
 seedless), 
 
 per cent 
 
 7.81 
 
 13.39 
 
 10.20 
 
 7.4 
 
 10 
 
 10.5 
 
 16 
 
 31.11 
 
 
 23.81 
 
 44.50 
 
 10.20 
 (seedless) 
 
Bulletin 322 THE EVAPORATION OF GRAPES 469 
 
 The results indicate that the loss in seeding of dried wine grapes 
 whose berries are above the average in size is not much greater than 
 that of Muscat raisins, while the loss in seeding dried wine grapes 
 with small berries (Petite Sirah) is about three times that of Muscat 
 raisins. The tests at least indicated that it is possible to remove the 
 seeds from such dried grapes, although it is doubtful whether such 
 a product could be produced as economically as seeded Muscat raisins. 
 
 The seeded Petite Sirah raisins were of excellent flavor and prac- 
 tically free from pieces of broken seeds. Tests were made of their 
 suitability for culinary use. Pies made from them resembled black- 
 berry pies in flavor, color and general appearance. A slightly 
 astringent flavor was noticeable if the dried grapes alone were used 
 but this defect was overcome when the raisins were mixed with an 
 equal quantity of chopped apples. These raisins will give excellent 
 results in various puddings, cookies, cakes, and candy in which they 
 may be used to replace Muscat raisins in the usual recipes. 
 
 If seeded dried red wine grapes can be produced and sold for a 
 price not greatly in excess of that received for Muscat or seedless 
 raisins it should be possible to develop an extensive market for them. 
 
 During the past season the dried grapes were sold in the un- 
 stemmed condition in sacks and boxes by some producers; others 
 packed the stemmed unseeded product in fifty-pound boxes. These 
 latter brought the best prices and it is probable that this method of 
 packing will be adopted generally in the future. 
 
 The machines used for stemming muscat raisins have proved satis- 
 factory for dried wine grapes, although as previously stated the raisins 
 must be thoroughly dry if satisfactory results are to be obtained. 
 
 VII. SUMMARY 
 
 1. An evaporator of the horizontal tunnel air-blast type and of 
 six tons of fresh fruit capacity per charge was constructed on the 
 University Farm at Davis during 1919 by funds furnished by the 
 State Board of Viticultural Commissioners and the University. This 
 evaporator was used successfully in the drying of grapes and prunes. 
 Plans, cost, and general specifications of this evaporator are to be 
 found in the text of this publication. Sketches indicating revised 
 evaporator plans recommended to growers have been given. The 
 recommended evaporator is of the same capacity and general appear- 
 ance as the University Farm evaporator but embodies the improve- 
 ments which we have found desirable to increase the efficiency of the 
 plant. The evaporator can be constructed for about $3,500. We 
 
470 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 believe the recommended evaporator to be equal in efficiency to any 
 evaporator of similar capacity now in use and superior to many. It 
 is not expensive to construct and can be erected by local artisans. 
 
 Most of the suggested improvements are now being made in our 
 plant. Therefore, growers who contemplate the erection of evapora- 
 tors are urged to visit the University Farm. 
 
 2. Dipping of grapes in a dilute boiling lye solution approximately 
 doubled the rate of drying. Most wine-grape varieties and Muscat 
 grapes require a lye solution of 2% to 3% for effective results. 
 Tokays and Thompson Seedless require only a %% solution. 
 
 3. Grapes dried in the evaporator were improved by a short period 
 of sulfur ing before drying. Much less sulfur ing was required for 
 grapes dried in the evaporator than for those dried in the sun. 
 
 4. No definite constant difference in yield could be found in sun- 
 drying and evaporation. The color and flavor of the juice obtained 
 by soaking sun-dried grapes in water was much inferior to juice 
 obtained from evaporated grapes. 
 
 5. The rate of drying is greatly increased by increase in tempera- 
 ture of the air used in drying. Temperatures up to 190° F. were 
 used successfully on red-wine grapes, although it was found necessary 
 to remove the grapes from the evaporator as soon as dry, to avoid 
 injury to color and flavor. A temperature of 165° F. may be used 
 in regular practice. 
 
 6. Recirculation of a large proportion of the exhaust air from 
 the evaporator greatly reduces fuel consumption without reduction 
 of the rate of drying. Recirculation prevents overdrying of the fruit 
 and permits regulation of moisture content of the dried product. It 
 is believed that higher temperatures of drying may be employed where 
 the humidity of the air used in drying is increased by recirculation. 
 
 7. The suction type of fan proved more satisfactory than the blast 
 type. The multivane fan was found to be much more efficient than 
 the disc type. 
 
 8. The air-blast distillate burner was more satisfactory than the 
 gravity burner, although both were used successfully. 
 
 9. Dried grapes of 25% or less moisture have kept perfectly; those 
 of 30% or over have spoiled unless heavily sulfured. The dried 
 product equalized rapidly in moisture content in sweat boxes. 
 
 10. Dried grapes stemmed satisfactorily when dried to about 10% 
 moisture and stemmed within a few hours after drying. 
 
Bulletin 322 THE EVAPORATION OF GRAPES 471 
 
 11. The dried grapes adhered with great tenacity to screen trays 
 but were easily removed from slat-bottom trays. Grapes dried as 
 rapidly on the latter as on the former. The slat-bottom trays are of 
 greater durability and lower cost than screen trays. 
 
 12. Dried wine grapes were seeded successfully but the loss during 
 this process was excessively large. The seeded product gave excellent 
 results when used for pies, puddings and other dishes. Dried white 
 wine grapes gave fair results on seeding but the finished product was 
 inferior to Muscat raisins. Seeded dried wine grapes appear to have 
 possibilities for culinary use. 
 
 13. Evaporator manufacturers. A list of manufacturers of evapo- 
 rators and dealers in evaporator equipment will be sent on request 
 made to the Division of Viticulture and Fruit Products. 
 
 14. Nomenclature. At the present time various terms are applied 
 more or less indiscriminately to fruits and vegetables from which most 
 of the water has been removed in order to preserve the product. At a 
 convention held in San Jose on evaporation a committee consisting of 
 A. W. Christie, Paul F. Nicholls, E. M. Sheehan, H. C. Rowley, and 
 S. C. Simons was .appointed to consider this question. The committee's 
 report, which has been approved by the College of Agriculture through 
 a committee consisting of J. C. Whitten, M. E. Jaffa, W. V. Cruess, 
 E. L. Overholser, and J. P. Bennet is as follows : 
 
 a. The same nomenclature shall be applied to fruits and vege- 
 tables. 
 
 b. The term " dried" is applied to all fruits and vegetables pre- 
 served by the removal of moisture, irrespective of the method of 
 removal. 
 
 c. There are but two classes of dried fruits and vegetables, namely, 
 those dried principally by solar heat and those dried principally by 
 artificial heat. 
 
 d. The class dried principally by solar heat shall be designated 
 ' ' sun-dried, ' ' by which is meant the removal of moisture by solar heat 
 without control of temperature, humidity, or air flow. 
 
 e. The class dried principally by artificial heat shall be designated 
 either "evaporated" or "dehydrated." The committee finds at this 
 time no sufficient reasons for distinguishing between "evaporated" 
 and "dehydrated." 
 
STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION 
 
 No. 
 168. 
 
 169. 
 185. 
 
 208. 
 230. 
 250. 
 251. 
 
 252. 
 253. 
 
 257. 
 261. 
 
 262. 
 
 263. 
 266. 
 
 267. 
 
 268. 
 270. 
 
 271. 
 272. 
 273. 
 
 274. 
 
 275. 
 
 276. 
 
 277. 
 278. 
 279. 
 280. 
 
 281. 
 
 282. 
 
 Observations on Some Vine Diseases 
 in Sonoma County. 
 
 Tolerance of the Sugar Beet for Alkali. 
 
 Report of Progress in Cereal Investi- 
 gations. 
 
 The Late Blight of Celery. 
 
 Enological Investigations. 
 
 The Loquat. 
 
 Utilization of the Nitrogen and Organic 
 Matter in Septic and Imhoff Tank 
 Sludges. 
 
 Deterioration of Lumber. 
 
 Irrigation and Soil Conditions in the 
 Sierra Nevada Foothills, California. 
 
 New Dosage Tables. 
 
 Melaxuma of the Walnut, "Juglans 
 regia." 
 
 Citrus Diseases of Florida and Cuba 
 Compared with Those of California. 
 
 Size Grades for Ripe Olives. 
 
 A Spotting of Citrus Fruits Due to the 
 Action of Oil Liberated from the 
 Rind. 
 
 Experiments with Stocks for Citrus. 
 
 Growing and Grafting Olive Seedlings. 
 
 A Comparison of Annual Cropping, Bi- 
 ennial Cropping, and Green Manures 
 on the Yield of Wheat. 
 
 Feeding Dairy Calves in California. 
 
 Commercial Fertilizers. 
 
 Preliminary Report on Kearney Vine- 
 yard Experimental Drain. 
 
 The Common Honey Bee as an Agent 
 in Prune Pollination. 
 
 The Cultivation of Belladonna in Cali- 
 fornia. 
 
 The Pomegranate. 
 
 Sudan Grass. 
 
 Grain Sorghums. 
 
 Irrigation of Rice in California. 
 
 Irrigation of Alfalfa in the Sacramento 
 Valley. 
 
 Control of the Pocket Gopher in Cali- 
 fornia. 
 
 Trials with California Silage Crops for 
 Dairy Cows. 
 
 BULLETINS 
 
 No. 
 283. 
 285. 
 286. 
 288. 
 
 290. 
 
 293. 
 296. 
 297. 
 298. 
 299. 
 
 300. 
 301. 
 
 302. 
 
 303. 
 304. 
 
 305. 
 
 307. 
 
 308. 
 
 309. 
 
 310. 
 311. 
 312. 
 313. 
 
 314. 
 316. 
 317. 
 
 318. 
 319. 
 320. 
 321. 
 322. 
 
 The Olive Insects of California. 
 
 The Milch Goat in California. 
 
 Commercial Fertilizers. 
 
 Potash from Tule and the Fertilizer 
 Value of Certain Marsh Plants. 
 
 The June Drop of Washington Navel 
 Oranges. 
 
 Sweet Sorghums for Forage. 
 
 Topping and Pinching Vines. 
 
 The Almond in California. 
 
 Seedless Raisin Grapes. 
 
 The Use of Lumber on California 
 Farms. 
 
 Commercial Fertilizers. 
 
 California State Dairy Cow Competi- 
 tion, 1916-18. 
 
 Control of Ground Squirrels by the 
 Fumigation Method. 
 
 Grape Syrup. 
 
 A Study on the Effects of Freezes on 
 Citrus in California. 
 
 The Influence of Barley on the Milk 
 Secretion of Cows. 
 
 Pollination of the Bartlett Pear. 
 
 I. Fumigation with Liquid Hydrocianic 
 Acid. II. Physical and Chemical 
 Properties of Liquid Hydrocianic 
 Acid. 
 
 I. The Carob in California. II. Nutri- 
 tive Value of the Carob Bean. 
 
 Plum Pollination. 
 
 Investigations with Milking Machines. 
 
 Mariout Barley. 
 
 Pruning Young Deciduous Fruit 
 Trees. 
 
 Cow-Testing Associations in California. 
 
 The Kaki or Oriental Persimmon. 
 
 Selection of Stocks in Citrus Propoga- 
 tion. 
 
 The Effects of Alkali on Citrus Trees. 
 
 Caprifigs and Caprification. 
 
 Control of the Coyote in California. 
 
 Commercial Production of Grape Syrup. 
 
 The Evaporation of Grapes. 
 
 No. 
 
 50. 
 65. 
 
 70. 
 
 76. 
 82. 
 
 87. 
 109. 
 
 110. 
 111. 
 
 113. 
 114. 
 115. 
 117. 
 
 124. 
 126. 
 127. 
 128. 
 129. 
 130. 
 131. 
 133. 
 
 Fumigation Scheduling. 
 
 The California Insecticide Law. 
 
 Observations on the Status of Corn 
 Growing in California. 
 
 Hot Room Callusing. 
 
 The Common Ground Squirrels of 
 California. 
 
 Alfalfa. 
 
 Community or Local Extension Work 
 by the High School Agricultural De- 
 partment. 
 
 Green Manuring in California. 
 
 The Use of Lime and Gypsum on Cali- 
 fornia Soils. 
 
 Correspondence Courses in Agriculture. 
 
 Increasing the Duty of Water. 
 
 Grafting Vinifera Vineyards. 
 
 The Selection and Cost of a Small 
 Pumping Plant. 
 
 Alfalfa Silage for Fattening Steers. 
 
 Spraying for the Grape Leaf Hopper. 
 
 House Fumigation. 
 
 Insecticide Formulas. 
 
 The Control of Citrus Insects. 
 
 Cabbage Growing in California. 
 
 Spraying for Control of Walnut Aphis. 
 
 County Farm Adviser. 
 
 CIRCULARS 
 No. 
 135. 
 136. 
 137. 
 138. 
 139. 
 
 140. 
 
 143. 
 
 144. 
 147. 
 148. 
 152. 
 
 153. 
 
 154. 
 
 155. 
 156. 
 157. 
 158. 
 159. 
 160. 
 
 Official Tests of Dairy Cows. 
 
 Melilotus Indica. 
 
 Wood Decay in Orchard Trees. 
 
 The Silo in California Agriculture. 
 
 The Generation of Hydrocyanic Acid 
 Gas in Fumigation by Portable 
 Machines. 
 
 The Practical Application of Improved 
 Methods of Fermentation in Califor- 
 nia Wineries during 1913 and 1914. 
 
 Control of Grasshoppers in Imperial 
 Valley. 
 
 Oidium or Powdery Mildew of the Vine. 
 
 Tomato Growing in California. 
 
 "Lungworms". 
 
 Some Observations on the Bulk Hand- 
 ling of Grain in California. 
 
 Announcement of the California State 
 Dairy Cow Competition, 1916-18. 
 
 Irrigation Practice in Growing Small 
 Fruits in California. 
 
 Bovine Tuberculosis. 
 
 Plow to Operate an Incubator. 
 
 Control of the Pear Scab. 
 
 Home and Farm Canning. 
 
 Agriculture in the Imperial Valley. 
 
 Lettuce Growing in California. 
 
CIRCULA RS— Continued 
 
 No. No. 
 
 164. Small Fruit Culture in California. 191. 
 
 165. Fundamentals of Sugar Beet Culture 193. 
 
 under California Conditions. 195. 
 
 167. Feeding Stuffs of Minor Importance. 
 
 168. Spraying for the Control of Wild 197. 
 
 Morning-Glory within the Fog Belt. 
 
 169. The 1918 Grain Crop. 198. 
 
 170. Fertilizing California Soils for the 199. 
 
 1918 Crop. 201. 
 
 172. Wheat Culture. 202. 
 173 The Construction of the Wood-Hoop 
 
 Silo. 203. 
 
 174. Farm Drainage Methods. 204. 
 
 175. Progress Report on the Marketing and 
 
 Distribution of Milk. 205. 
 
 176. Hog Cholera Prevention and the Serum 206. 
 
 Treatment. 207. 
 
 177. Grain Sorghums. 208. 
 
 178. The Packing of Apples in California. 
 
 179. Factors of Importance in Producing 209. 
 
 Milk of Low Bacterial Count. 210. 
 
 181. Control of the California Ground 213. 
 
 Squirrel. 214. 
 
 182. Extending the Area of Irrigated Wheat 
 
 in California for 1918. 215. 
 
 183. Infectious Abortion in Cows. 216. 
 
 184. A Flock of Sheep on the Farm. 
 
 185. Beekeeping for the Fruit-grower and 217. 
 
 Small Rancher or Amateur. 
 
 187. Utilizing the Sorghums. 218. 
 
 188. Lambing Sheds. 
 
 189. Winter Forage Crops. 219. 
 
 190. Agriculture Clubs in California. 
 
 Pruning the Seedless Grapes. 
 
 A Study of Farm Labor in California. 
 
 Revised Compatibility Chart of Insecti- 
 cides and Fungicides. 
 
 Suggestions for Increasing Egg Produc- 
 tion in a Time of High-Feed Prices. 
 
 Syrup from Sweet Sorghum. 
 
 Onion Growing in California. 
 
 Helpful Hints to Hog Raisers. 
 
 County Organization for Rural Fire 
 Control. 
 
 Peat as a Manure Substitute. 
 
 Handbook of Plant Diseases and Pest 
 Control. 
 
 Blackleg. 
 
 Jack Cheese. 
 
 Neufchatel Cheese. 
 
 Summary of the Annual Reports of the 
 Farm Advisors of California. 
 
 The Function of the Farm Bureau. 
 
 Suggestions to the Settler in California. 
 
 Evaporators for Prune Drying. 
 
 Seed Treatment for the Prevention of 
 Cereal Smuts. 
 
 Feeding- Dairy Cows in California. 
 
 Winter Injury or Die-Back of the Wal- 
 nut. 
 
 Methods for Marketing Vegetables in 
 California. 
 
 Advanced Registry Testing of Dairy 
 Cows. 
 
 The Present Status of Alkali.