UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA Precooling of Fresh Fruits and Temperatures of Refrigerator Cars and Warehouse Rooms E. L. OVERHOLSER and B. D. MOSES BULLETIN 496 JUNE, 1930 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1930 FOREWORD This bulletin is a contribution of the Division of Pomology, the Division of Agricultural Engineering, and the California Committee on the Relation of Electricity to Agriculture. It is the sixth of a series planned to report the results of investigations conducted jointly by the Agricultural Experiment Station, College of Agriculture, Uni- versity of California, and the California Committee on the Relation of Electricity to Agriculture.* This committee represents the agri- cultural and electrical industries in California that are working together for the purpose of making reliable information available concerning the use of electricity on the farm, and of cooperating with similar committees in other states. C. B. Hutchison, Director, California Agricultural Experiment Station. The personnel of this committee for 1929-30 is: H. B. Walker, College of Agriculture, Chairman. Alex. Johnson, California Farm Bureau Federation, Vice-Chairman. N. E. Sutherland, Pacific Gas and Electric Company, Treasurer. B. D. Moses, College of Agriculture, Director-Secretary. J. E. Tavernetti, College of Agriculture, Field Engineer. C. L. Cory, College of Mechanics, University of California. H. M. Crawford, Pacific Gas and Electric Company. W. J. Delehanty, General Electric Company. J. J. Deuel, California Farm Bureau Federation. A. M. Frost, Great Western Power Corporation. Charles Grunsky, Standard Management and Operating Corporation. T. H. Lambert, Agriculturist. E. C. McFadden, Southern California Edison Company. W. C. McWhinney, Southern California Edison Company. E. G. Stahl, San Joaquin Light and Power Corporation. George Tenney, McGraw-Hill Publishing Company. PRECOOLING OF FRESH FRUITS AND TEMPERA- TURES OF REFRIGERATOR CARS AND WAREHOUSE ROOMS E. L. OVERHOLSEEi and B. D. MOSES2 The term "precooling" refers to the process of cooling the fruit soon after harvesting", and before it is shipped. The degree of maturity at which the fruit can be picked and the condition in which it arrives at its destination depend greatly upon its temperature after harvest, both before and during transit. The more nearly fruit is picked at the proper stage of maturity for the best development of color and highest subsequent eating quality, the greater is the neces- sity for precooling. Fruit when picked from the tree is not inert. After harvesting it continues metabolic or ripening activities for a variable period of time, depending upon the conditions that surround it. As a result of these metabolic activities, the tissues of the fruit gradually become overripe and break down. These changes may be retarded, and decay checked, by cooling the fruit promptly after it has been harvested, and keeping it at a relatively low temperature until used. The rate at which fruit ripens may be reduced as much as one-half for each 15° Fahrenheit drop in the temperature at which it is held, within ripening temperatures. Overholser, Winkler and Jacob (5) found that fruit exposed to the sun even while on the tree may be from 7° to 10° F warmer than the surrounding air. Peaches have been observed to increase 1.26° F in ten hours when kept in air at 50°, and 6.57° when in air at 86°. (2) It has been computed that sound apples held at a temperature of 68° F generate heat at the rate of about 0.012 calories per second per kilogram, because of their own self -heating. (3) This amounts to about 3740 B.t.u. per ton of apples per twenty-four hours, which is sufficient heat to melt about 26 pounds of ice. Raspberries would develop nearly five times, peaches twice, and oranges one-third as much heat as apples. The self -heating of fruit and the relatively small amount of refrig- eration required to check it, and the value of rapid reduction of field 1 Formerly Associate Professor of Pomology, University of California. 2 Associate Professor of Agricultural Engineering, University of California. 4 University of California — Experiment Station temperatures of fruit seem to justify precooling by mechanical refrig- eration, particularly when it is to be placed in insulated compartments, provided with limited refrigeration, such as refrigerator cars. In the case of fruit to be loaded into ships, precooling enables it to be held temporarily, pending the accumulation of the cargo or the arrival of the ship, and reduces losses in case of delays resulting from unfavorable weather at sea. Precooling of fruit to be loaded also prevents the placing of warm fruit with a cargo that has been satis- factorily cooled, a procedure producing a condition favorable to mold. It has been found that a number of rot organisms would continue to grow at 32° F, after the spores had germinated at higher tempera- tures. The growth at 32° is, however, not so rapid nor so extensive as at higher temperatures. The germination and growth of the spores of blue mold (Penicillium expansum) , which may cause serious rotting of apples in storage, is inhibited at temperatures of 30° to 32° F. These results indicate that delay in cooling results in greater losses from rots than when the temperature is lowered quickly before the fruit is placed in storage rooms or refrigerator cars, Precooling, under many conditions, may, therefore, be expected to lessen losses from rots. Ramsey (7) determined the average' fruit temperatures during transit between Wenatchee, Washington, and Chicago, Illinois, in a standard refrigerator car loaded with apples. He found that 114 hours, with four re-icings, were required to reduce the temperature from 62° to 45° F, the maximum temperature for the most successful shipping, and that four additional days were required to reduce it to 40°. Ridley (9) in his studies of the distribution of refrigeration in a car of strawberries en route from southwestern Missouri to St. Paul, Minnesota, found a difference of 10° F between the fruit in the top and that in the bottom containers. This difference is sufficient to permit marked variation in the rate of ripening or the degree of spoiling of the fruit. In 1924 observations were conducted by The California Fruit Exchange upon fruit being shipped in standard refrigerator cars to Chicago and New York. The temperature of the fruit throughout the top layers averaged from 9° to 16° F higher than in the bottom layers. At the start the fruit in the top layers averaged 20° higher than in the bottom layers. This condition prevailed with an outside air temperature of between 80° and 90° and a fruit temperature when loaded of around 75° to 80°. The temperature of the fruit at the bottom of the load near Bul. 496] Precooling of Fresh Fruits the ice bunkers dropped to 45° or thereabout within 12 hours after the car doors were closed, but it took four days for the temperature of the fruit in the top of the load, half way between the ice bunkers and center bracing, to drop to 55°. Because of the interest shown, by shippers of California fruit, in equipment that could be used to cool the fruit before shipment, and because there seemed to be little information upon the rate at which fruit cools under different conditions, an investigation was made by the California Committee on the Relation of Electricity to Fig. 1. — Fruit being precooled, before loading into refrigerator car, in a room in a cold storage warehouse. The fruit is placed in these rooms equipped with air ports at either end connecting with ducts through which refrigerated air is blown. The temperature ordinarily maintained in the ducts is between 28° and 32° F, and regulation is effected by controlling the flow of air. Agriculture and by the Division of Pomology of the College of Agri- culture, University of California, on the temperature changes in certain fruits as affected by different methods of precooling. This investi- gation covered two distictive systems, warehouse and car precooling. Under the warehouse system the fruit is packed, placed in cold storage rooms, and cooled to between 30° and 34° F. It is then loaded directly into iced refrigerator cars, stowed in the refrigerated holds of ships, or stored in cold storage warehouses for subsequent shipment. The air around the fruit may be cooled quickly, but the package and its contents give up their heat slowly. Under favorable con- 6 University of California — Experiment Station ditions in a cold storage warehouse, according to Powell, (6) the fruit in the center of a barrel of Bartlett pears stored at a temperature of 30° F required four to seven days to cool from 80° to approximately the temperature of a cold storage room. Similar fruit in a 20-pound box or in a bushel salt crate reached 32° F in from 12 to 24 hours. In a storage room approximating 32° F, according to Whitehouse (11) it required 30 hours for the temperature in the center of a box of wrapped apples to drop from 70° to 40° F and an additional 130 hours to drop to 34°. In other words, the temperature in the box dropped 30° degrees during the first 30 hours and but 6° in the next 130 hours. One of the railroad companies in southern California employs a method for car precooling which consists of hauling the loaded refrigerator cars to a central plant built along the track at a point en route, and causing cold air to be blown through each car. This air enters the hatch at one end of the car, circulates around the fruit, passes out at the other end, and returns to the cooling rooms of the plant. The direction of air flow may be reversed at intervals if desired. The capacity is 26 cars at a time, and the period of pre- cooling averages about two hours. The temperature in the car may be lowered to 40° F in order to hasten the cooling of the cargo and lessen the need of subsequent re-icing. Recently there has been increasing interest in portable car pre- coolers which enable the cars to be precooled at the point of loading. Although the details of construction and operation may differ some- what, the various makes all employ some system of circulating air from the ice bunkers around the fruit containers. Forced air cur- rents from fans either inside or outside the car, are controlled by air ducts, baffles, and partitions. The ice in the bunkers of the car is used to supply the refrigeration, and the circulation of the air hastens the transfer of heat from the fruit to the ice. Salt may or may not be added to the ice in the bunkers. After 6 to 8 hours of operation of the car precooler it is necessary to re-ice at the nearest icing point en route. TEMPERATURE STUDIES OF REFRIGERATOR CARS AND WAREHOUSES A study was made of the following: (1) air and fruit temperatures in commercial warehouse cold-storage rooms used for precooling; (2) air and fruit temperatures at different positions within the re- frigerator car, as affected by car precooling; (3) the rate of tempera- Bul. 496] Precooling of Fresh Fruits ture drop in the fruit within the packages and in the air outside the packages; and (4) the differences in rate of temperature fall as affected by the kind of fruit and type of package. Copper-constantan thermocouples and resistance thermometers were used for the measurements. The size of the thermocouple junc- tions was such that they could be inserted in even the smaller fruits, and the leads varied from 24 to 30 feet in length, so that the tempera- ture readings could be made, by means of multiple switches, without Fig. 2. — Fruit and air temperatures in a refrigerator car were taken with thermocouples attached through rotary switches to a suitable meter by leads suf- ficiently long to reach all parts of the car. The junctions of these couples were small enough to give the temperature at the center of a pear or even of a grape or cherry. The flexible leads permitted observations on a fruit in the center of a package in the center of a stack anywhere in the closed car. Three switches with a total capacity of 40 points were used. The leads, one of the two switches, and the meter are shown. The recording thermometer records air temperatures in the center of the car. entering the car. Standardized mercury thermometers and recording hygro-thermographs were also used. To insure accuracy the thermo- couples and resistance thermometers were carefully calibrated before and after each test. The discussion of the experimental data deals first with the warehouse precooling and second with the individual or portable car precooling units. University of California — Experiment Station WAREHOUSE PRECOOLING OF PEARS, GRAPES AND ORANGES Pears. — One set of tests was made in a large cold storage room, which was loaded with pears to about 70 per cent of its capacity. Air at a temperature of approximately 32° F was continuously blown from inlet ducts into and throughout the room and its contents with sufficient velocity and volume to give a complete change of air about Yig. 3. — Fruit stored in cold room of cold storage plant, showing method of stacking so as to maintain aisles for handling the different lots, and the method of spacing so as to facilitate air circulation between the boxes. The wires toward the center are thermocouple leads for observing fruit and air temperatures. every three minutes when the room was empty (see fig. 3). The relative humidity varied from 80 to 86 per cent at the air inlet ducts to from 89 to 91 on the air outlet side of the room, after the air had passed over the fruit. The data in table 1 showed that it required a relatively long time to remove the heat from wrapped pears packed in the center of Bul. 496] Precooling of Fresh Fruits standard boxes. For example, when Bosc, Hardy, and Winter Nelis pears, having an initial temperature of about 61.5° F, were placed in a room maintained at approximately 32° to 36°, the fruit in the center of the boxes did not cool to 35° until after 44 hours. The temperature was not further lowered after six hours' additional time. TABLE 1 Average Bate of Temperature Drop in the Center of Wrapped Pears and in the Space Between Pears in the Center of Packed Boxes in Cold Storage Precooling Booms (San Jose, California) Time of observation Temperature in degrees Fahrenheit In center of pears in center of boxes Between wrapped pears in center of boxes In air Date Hovir channels between boxes f Sept. 15, 1927 12:15 p.m. 2:12 p.m. 4:10 p.m. 7:05 p.m. 9:10 p.m. 8:40 a.m. 12:45 p.m. 5:25 p.m. 10:10 p.m. 8:15 a.m. 2:15 p.m. 61.5 57.3 55.4 54.2 52.5 43.4 41.8 40.2 38.0 35.3 34.5 61.0 57.0 55.2 53.7 52.4 43 4 41.1 40.2 38.1 35.6 35 35.5 35.0 34 9 33.7 32.9 32.2 33.6 35.3 32.7 31.9 33.3 Sept. 16, 1927 J Sept. 17, 1927 / There was no marked difference between the temperature drop of wrapped pears in the center of a box and that of the air immedi- ately surrounding the fruit. Under such conditions of tight packing the cooling within the box is largely by conduction, there being little or no air movement within the package. Stubenrauch and Ramsey (10) determined that loose pears in lug boxes cooled to the desired temperature in less than half the time required for wrapped, packed pears. With the packed boxes it fre- quently required three times as long to cool the fruit in the center of the box as to cool the outer fruit in the same box. Powell (6) re- ported that fruit wrappers retarded cooling, and that there may be a difference of 10° F in temperature of the fruit at the end of one day, between 40-pound boxes of unwrapped and of wrapped fruit. Beach and Eustace (1) found that with barrelled apples held at 34° F for 74 hours, unwrapped fruit had dropped to 38.5°, while wrapped fruit had dropped to only 43°. Unwrapped fruit in a bushel box dropped to 35° in 58 hours, whereas 70 hours were required for a similar drop when the fruit was wrapped. 10 University of California — Experiment Station As shown in table 2, the temperature of the center of the fruit the center of the box was brought to 33.2° F after 45 hours of The temperature of the air immediately surrounding the m cooling. TABLE 2 Bate of Temperature Drop in the Centers of Wrappe;d Pears and in the Space Between Pears in the Center of Packed Boxes in PrecoO'Ling Warehouse Rooms (Exeter, California) Time of observation Temperature in degrees Fahrenheit In center of pears in center of boxes Between wrapped pears in center of boxes Date Hour Air in warehouse room Sept. 29, 1927 11:30 a.m. 12:30 p.m. 4:00 p.m. 8:05 p.m. 9:50 p.m. 9:00 a.m. 2:00 p.m. 5:00 p.m. 8:00 p.m. 8:30 a.m. 74.8 70.6 66.0 64.0 58.8 48.0 44 40.4 38.8 33.2 74.0 69.4 64.8 61.1 58.6 46 3 41.4 39.9 38.7 31.9 42.5 39.8 36 35.0 32.5 31.8 30.3 Sept. 30, 1927 < Oct. 1, 1927 29.8 29.3 31.5 fruit in the center of the box was slightly lower than the temperature of the fruit itself, possibly because the fruit was not quite so tightly packed as was the case in the first test shown in table 1. Grapes. — Grapes cooled somewhat more rapidly than did pears, possibly because the individual fruits were not placed so tightly TABLE 3 Average Change of Temperature in the Center of Boxes of Black Cornichon and Malaga Grapes in Warehouse Precooling Eooms (Exeter, California) Time of observation Temperature in degrees Fahrenheit Date Hour In boxes of grapes Air in room Sept. 29, 1927 Sept. 30, 1927 J Oct. 1, 1927 11:00 a.m. 12:30 p.m. 4:00 p.m. 8:10 p.m. 9:50 p.m. 9:00 a.m. 2:00 p.m. 5:00 p.m. 8:00 p.m. 8:30 a.m. 59.5 57.4 52.9 48.1 45 5 39.6 36.4 35.2 34.7 32.8 40.4 39.2 36 35.1 32.6 31.7 30 4 29 9 29.3 30 5 Bul. 496] Precooling of Fresh Fruits 11 together, were not wrapped, and were smaller. Hence, the cooling resulted not only from conduction but also to some extent from air movement between the fruits. Furthermore, the grapes, being smaller, have a larger cooling surface per unit volume than do pears, and this would permit more rapid cooling. The complete cooling required a longer time than seems usually to be believed. The centers of boxes of Black Cornichon and Malaga grapes having a temperature of 60° F were cooled to 35° after 30 hours in the cold storage room. It required an additional 15 hours to reduce the tem- perature to 33°. The boxes of grapes on the floor tended to cool some- what more rapidly than did those on the top of the stack (see table 4). TABLE 4. Average Change in Temperature in the Center of Boxes of Black Cornichon and Malaga Grapes in the Top and Bottom Positions in the Stacks in Warehouse Precooling Booms (Exeter, California) Time of observation Temperatures in degrees Fahrenheit Date Hour In top boxes In bottom boxes Air adjacent to top boxes Air adjacent to bottom boxes Sept. 29, 1927 Sept. 30, 1927 < Oct 1, 1927 11:00 a.m. 12:15 p.m. 4:00 p.m. 8:10 p.m. 9:50 p.m. 9:00 a.m. 2:00 p.m. 5:00 p.m. 8:03 p.m. 8:30 a.m. 63.0 59.8 53.9 49.7 48.3 42 7 37.8 36.4 35.1 33 55 53 48 43 41 36 34 33 33 31 3 2 2 8 3 3 2 9 2 9 42.1 39.8 36.0 35.4 33.1 31.8 30.4 29.9 29.5 30 5 40.0 38 5 35.4 34.7 32, 5 31.6 30.3 29.8 29.0 30 4 There was a greater temperature difference between the centers of boxes of grapes at the top and at the bottom of the stacks than would be expected from the temperature differences of the air. This may, however, be explained by the differences in rate of air flow around the grapes in the two positions. A drop curtain was used to deflect the air travelling across the room through the fruit ; it extended nearly the entire length of the room and reached from the ceiling to below the top boxes. The air velocity along the floor, between the stacks of fruit in the middle of the room, was 52 feet per minute, whereas six boxes above the floor it was only 5 feet per minute. Granges. — Boxes of packed, wrapped Valencia oranges were set on end in a precooling room several feet from the nearest boxes. There were two sizes of oranges, one averaging 2% inches in diameter, 12 University of California — Experiment Station packing 200 to the box, and the other averaging 3% inches in diameter and packing 126 to the box. The rate of cooling in the center of the oranges in the middle and in the periphery of the box is shown in table 5. Fig. 4. — Fruit placed in cold storage room. The air enters through ports in the ceiling near one side wall, flows across the room, and passes out of ports similarly placed near the opposite wall. A canvas curtain is dropped from the ceiling to within about five feet of the floor. This curtain prevents short-circuiting of the cold air across the tops of the boxes. The wires shown are leads from thermocouples placed in the fruit and air spaces. TABLE 5 Average Change of Temperature in the Center of Packed, Wrapped Valencia Oranges in Warehouse Preicooling Rooms (Pomona, California) Temperature in degrees Fahrenheit Time of observation Inside of 2%-inch orange Inside of 3MJ-inch orange Average Date Hour In center of one end of box In outside row of one end of box In center of one end of box In outside row of one end of box of air in room 4:00 p.m. 4:05 p.m. 5:05 p.m. 7:00 p.m. 9:00 p.m. 7:00 a.m. 10:00 a.m. ^2:00 p.m. 6:00 p.m. 10:00 p.m. 7:00 a.m. 11:00 a.m. 3:00 p.m. 10:00 p.m. 8:00 a.m. 74.7 75.3 73.8 71.8 59.0 55.8 51.8 48.5 45.5 41.0 39.5 38.8 36.8 35.3 71.0 Fruit p 61.5 56 53.0 44.0 42.3 40.5 39.0 37.3 35.3 34.8 34.8 33.8 33.3 73 3 ut in cold 73.5 72 5 70 56.5 53.5 49.3 46.3 43.8 39.3 37.8 36.8 35.5 34.5 72.3 room. 65 3 58.5 54.8 44.3 42.3 40.5 39.0 37.5 35.0 34.5 34 5 34.3 33 June 18, 1928 June 19, 1928 June 20, 1928 35 35 34.6 33.3 33.3 33.7 33.0 32 5 31.8 32.7 33.3 33.3 32.5 Bul. 496] Precooling of Fresh Fruits 13 It is strikingly interesting* that oranges cooled more slowly than any of the other fruit studied. Not less than 64 hours was required to cool oranges in the centers of each half of the divided box from about 74° to about 35°, the boxes being surrounded by air of approxi- mately 33° F. The oranges in peripheral portions of the box cooled somewhat more rapidly than did those in the center. The relatively large size of the fruits, the high water content, and the insulating effect of the thick protective rind, no doubt account for the slowness with which oranges can be precooled. Fig. 5. — Section of refrigerator car loaded with fruit packed in containers of different shapes and sizes, showing the natural circulation of the air downward through the ice and upward through the fruit. Some precoolers (fig. 8) oppose natural convection currents and force the air to circulate in the opposite direction. Others increase the flow in the natural direction, and still others (fig. 9) by letting the air into the car at one hatch on top of the car and out at the other, combine the two principles; in one end the air goes with the natural flow; at the other end, against it. Several packing houses in southern California are precooling oranges. The packed oranges are placed in temperatures of from 32° to 34° F for from three to ten days and are thus precooled to approxi- mately 34°. They are then loaded directly into the iced car. The bunkers contain 23 blocks of ice weighing 315 pounds each and making about 14,500 pounds of ice to the car. After the car is loaded and braced, which requires about an hour, the hatches and doors are sealed with instructions not to re-ice en route. The precooled fruit thus begins the journey at a temperature of about 36° F. Through the courtesy of the California Fruit Growers' Exchange, data were obtained for 23 precooled cars shipped east from Pomona, California. With these precooled oranges the temperature of the fruit was eleven days in gradually rising from 34° to about 45° F. There was 14 University of California — Experiment Station relatively little difference between the fruit temperatures in the differ- ent parts of the cars en route. The difference averaged 2.5° F. On the average the bunkers were still half full of ice when the cars reached their destinations, and the per cent of fruit decay was negligible. Fig. 6. — a portable car precooler consisting of four fans mounted on vertical shafts and driven by individual electric motors, mounted in a metal frame. The unit rests on the bracing at the center of the car, draws air from the ice bunkers over the fruit, and forces it downward between the boxes and toward the bunkers. Bul. 496] Precooling of Fresh Fruits 15 FIRST TYPE CAR PRECOOLER STUDIED The first type of car precooler studied consisted of four %-horse- power vertical electric motors directly connected with propeller fans and mounted on a horizontal carriage, which was placed in the door- way space between the bracing of a loaded car. A canvas cover was spread over the top tier in each end of the car from the bunker to the fan carriage and securely fastened in place by means of three adjustable horizontal struts which reached from side to side of the Fig. 7. — The blowers of this car precooler are carried on a special truck from which they are slid on to the bracing. The platform is adjustable as to height, and the whole frame is mounted on rockers. car. This sheet prevented the short-circuiting of the air upwards between the tiers of boxes and directed it backwards through the fruit to the lower half of the bunkers. When the fans are in operation, cooled air is drawn forward from the top of the ice bunkers over the canvas, forced downward at the space between the bracing, and sent backward through the tiers of boxes and around the fruit to the bottom of the ice bunkers. The warmed air then passes upward through the ice, releasing heat absorbed from the fruit, and out again at the top of the ice bunkers, to be recirculated. The theory advanced by the manufacturers in support of this direction of air flow is that the coldest air comes into contact with the warmest fruit at the center of the car, and the some- what warmed air reaches the fruit nearest the bunkers which, under 16 University of California — Experiment Station natural conditions, is in the coldest position of the car. The general practice is to run the precooler for from five to eight hours and to close the doors as quickly as possible when it is removed. The car should be re-iced as soon as possible in order to replace the ice that has been melted during precooling. Numerous tests of the air and fruit temperatures as affected by this type of car precooler were made. The refrigerator cars were all modern, fitted with standard equipment and in good condition. Some had been recently overhauled. In every case the bunkers were nearly full of ice at the time the car was loaded. FANS vvi MOTORS ARROWS MNOTf OtRtCTION Of AIR Fig. 8. — Sectional view of a standard refrigerator car with a car precooler in position. This type draws the air through the ice bunkers and then recirculates it through the load from the center of the car towards the ends. The canvas sheets prevent shortcircuiting of the air and are raised at the center because of the air pressure developed by the fans. Air Temperatures. — The average air temperatures in different positions of the car as influenced by the operation of the car pre- cooler were determined. Representative data, obtained from three cars, one loaded with mixed containers of plums, grapes, peaches, and pears, the second with pears, and the third with grapes, are shown in table 6. The data indicate that the average air temperatures, during four hours operation of the car precooler, did not drop below 45° F. During the operation of the precooler and afterwards the coldest air temperatures tended to be near the floor, particularly under the false floor at the bracing and at the bunker, the warmest air being found at the top of the load of fruit midway between bracing and bunker and near the bunker. The air temperature differences between various parts of the car were, however, reduced to a minimum during Bul. 496] Precooling of Fresh Fruits 17 the operation of the car precooler. There was less difference in air temperature between the top and bottom of the load at the bracing than between top and bottom at the bunker. When the car precooler was stopped, however, the differences between air temperatures at the bunker, the bracing", the top, and the bottom, became marked. TABLE 6 Air Temperature Changes in Standard Loaded Refrigerator, Cars During and Subsequent to Operation of Car Precooler, in Degrees Fahrenheit (Mayhews, California, September 19, 1927)* Bottom, near bunker Top, near bunker Bottom, near bracing Top, near bracing Bottom, midway bunker and door Top, midway bunker and door Precooler Fans Started 1 p.m. 44 1 63.5 47.1 54 .3 48.2 52 1 46.0 50 5 45.8 50 2 46.0 50 3 47.3 49.9 45 .1 48.5 4/0 48.3 48.0 47.8 47.5 48 48.2 45.5 52.5 52.9 49.7 46.9 46.6 47.3 47.4 48.2 61.0 52.1 51 49.7 49.2 48.3 48.5 47.1 Precooler Fans Stopped 5 p.m. 43.9 48.2 46.2 48 45.8 49.1 38.9 52.1 45 50.8 41 9 51 5 38.9 53.2 45 52 41.8 52.8 38.8 54.5 47.8 52.5 42 4 54 39 55.6 46.8 52 5 42 3 54 3 Readings tabulated for half-hour intervals. The temperature changes indicate definitely that when the fans were stopped there was a reversal in direction of the air currents from that during: the operation of the fans. The temperature changes within the cars were appreciably influ- enced, first, by the amount of ice in the bunkers, and second, by the size of the air channels formed between the cakes of melting ice. When the ice was compacted with a tamp, a slight temperature drop in the car resulted. The effect of the sun shining directly on one end of the car was indicated by the temperature measurements becoming somewhat higher there than in the opposite end. Method of Taking Fruit Temperatures. — The studies on the tem- peratures of the fruit, as taken by inserting thermometers into the fruit itself, show a decided lag in the lowering of temperature of the fruit behind that of the air in the car, of the air between the 18 University of California — Experiment Station containers, and even of the air within the containers. Each precau- tion taken to protect the fruit against physical injury increases the insulation of the fruit against heat removal. Thermometers placed in the air in the car, at best can be taken only as indicators, and should be placed as near the fruit as possible. Each fruit is discussed inde- pendently under the following tables. Temperatures in Packed Pear Boxes. — Temperature measurements were made in the spaces between fruits and in the centers of pears at the bulge and center of the boxes. The data in table 7 show the lag in temperature drop just within the bulge of boxes of pears as contrasted with the air temperatures in the channels between boxes. On the other hand, after the fans were stopped, the temperature just within the bulge tended to rise more rapidly than the air temperature. This increase was probably the result of the heat of the fruit within the package. TABLE 7 Average Rate; of Temperature Drop in the Bulge, of Boxes of Pears in Refrigerator. Cars During and After Operation of Car Precooler (Mayhews, California) Time of observation Temperature in degrees Fahrenheit In bulge of boxes of pears In air channels Date Hour between boxes Sept. 19, 1927 1:25 p.m. 66.4 67.9 Precooler Fans Started Sept. 19, 1927. 2:30 p.m. 62.8 58 1 4:25 p.m. 52.8 46.0 6:30 p.m. 50 7 45.2 8:30 p.m. 48.8 44 3 Precooler Fans Stopped Sept. 20, 1927.. 9:00 p.m. 5:30 a.m. 7:30 a.m. 9:30 a.m. 11:30 a.m. 2:30 p.m. In order to determine the difference in the rate of temperature drop within the fruit itself and in the surrounding air, thermocouples were inserted into the center of wrapped pears and in the space between them as the boxes were being packed. Three such boxes were prepared and with the attached wires were placed in the tier Bul, 496] Precooling of Fresh Fruits 19 second from the top and midway between the sides of a car loaded with pears. One box was placed next to the bunker midway between the sides of the car; the second box midway between the bunker and the bracing" at the door ; and the third at the bracing". Average tem- peratures for the boxes and for the air of the car are shown in table 8. TABLE 8 Temperature Changes in the Center of Pears Packed in Boxes and Loaded in Refrigerator Cars During and After Operation of Car Precooler (Mayhews, California) Average temperature in degrees Fahrenheit Time of observation In center of pears in center of box In air next to pears in center of box In air sur- rounding box Date Hour containing pears August 20, 1927 6:30 p.m. 69.5 69.5 67.8 Car Precooler Started August 20, 1927.. August 21, 1927. 7:00 p.m. 9:00 p.m. 11:00 p.m. 1:00 a.m. 59.9 48.5 45 43.3 Car Precooler Stopped 1:30 a.m. 59.0 58.8 46.2 7:30 a.m. 57.0 56.8 51.3 August 21, 1927 9:30 a.m. 11:30 a.m. 57.2 59 57.3 58.8 51 5* 52 2 1:30 p.m. 3:30 p.m. 59.3 58.7 58.3 57 3 53.4 53.5 1 5:30 p.m. 58.0 57,3 53.7-,,,., * Six thousand pounds of ice added to car bunkers. A test was also conducted with a car containing plums and grapes as well as pears. The temperature of the pears in the mixed car did not drop so satisfactorily as in the cars loaded with pears only. The difference in the size of the boxes necessitated loading in such a manner that continuous air channels extending from the bunkers to the bracing and from the floor to the top of the load could not be left between the rows of boxes. The temperature measurements indi- cated that loading, stripping, and bracing, so as to form continuous air channels, facilitate the lowering of the temperatures uniformly and effectively during and after the operation of the car precooler. These data are shown in table 9.. 20 University of California — Experiment Station TABLE 9 Changes in Temperature in the Ceinter of Packed Pears in a Mixed Befrigerator Car Containing also Plums and Grapes, During and After Operation of Car Precoo at Different Hours of the Day (August 19, 1927, Mayheiws, California) Hours delivered to packing shed Average temperature of fruit, degrees Fahrenheit 9:00 a.m. 70 10:00 a.m. 75 11:15 a.m. 78 1:00 p.m. 80 3:50 p.m. 86 4:30 p.m. 89 5:20 p.m. 91 6:10 p.m. 92 7:00 p.m. 88 8:45 p.m. 77 There were differences of as much as 22° in the temperatures of the delivered pears, depending upon the time of the day the fruit was picked. After being placed in the packing shed, however, the loose fruit in lug boxes from the field gradually attained the tempera- TABLE 20 Average Drops in Temperature in the Centers of Packages of Different Fruits in Refrigerator Cars During Operation of Car Precoolers and in Warehouses; Degrees Fahrenheit Kind of fruit Wrapped, packed boxes of pears Grapes packed in lug? Wrapped, packed boxes of oranges Wrapped, packed boxes of pears Grapes packed in lugs Packed boxes of cherries Packed crates of apricots Wrapped, packed boxed peaches Wrapped, packed boxed peaches Packed boxes of tomatoes Packed crates of cantaloupes Method of precooling Warehouse Warehouse Warehouse Car-precooler.. Car-precooler.. Car-precooler.. Car-precooler.. Car-precooler.. Iced car only... Car-precooler.. Car-precooler.. Hours of pre- cooling 45.0 33.0 64.0 6.0 3.0 6.0 3.5 7.0 7.0 5.0 6.0 Initial fruit temper- ature 68.6 59.5 74.0 69.5 60.8 60.0 78 60.0 56.0 71.8 71.9 Initial temper ature of cooling air 39.0 40.4 35.0 67.8 54 2 56.0 64.2 44 52.9 63.5 67.8 Final fruit temper- ature 34.2 34.7 34.9 59.7 51.5 43.3 64.4 44.6 54.2 60.1 54.9 Final drop in fruit temper- ature 41 53 37.8 49.7 44.4 47.2 Total drop in fruit temper- ature 34.4 24.8 39.1 9.8 9.3 16.7 13.6 15.4 1.8 11.7 17.0 ture within the shed and followed shed temperature changes rather closely. Representative specimens of this same fruit were left in the packing house overnight, and the next morning the temperature of the fruit in open lugs averaged 60.8° F. This was nearly 10° colder Bul. 496] Precooling of Fresh Fruits 31 than the coolest fruit brought from the field the preceding day, and 31° cooler than the warmest fruit. In many of the fruit-growing sections of the state, during the harvesting season, there may be as much as 50° difference in air temperature between the cool hours of the night and the warm hours of the day. It therefore appears to be desirable, when packing house space, loading facilities, car supply, and working conditions permit, to store the fruit picked overnight in the cooler, ventilated parts of the shed in the afternoon. As a result of the lower night temperatures and the exchange of air surrounding such loose fruit in lug boxes when properly placed to permit ventilation, it can be packed the following morning at a lower initial temperature than would be attained with eight hours of car precooling. Then with the proper use of car precoolers the fruit could be further cooled and started on its journey in a condition approaching the temperatures that are desired en route. SUMMARY AND CONCLUSIONS 1. In the warehouse, when the pears were surrounded by air currents having temperatures of 30° to 35° F it required from 45 to 50 hours to cool the centers of the fruit packed in the centers of standard boxes, from 60°-75° F down to 33°-35° F. Extraction of the heat from wrapped, packed pears is primarily by conduction. 2. Packed boxes of grapes cooled somewhat more rapidly than did packed boxes of pears. With grapes the individual fruits were not so tightly packed together and were unwrapped. Grapes were cooled from 60° down to 35° F in about 33 hours in a warehouse. 3. The precooling of wrapped oranges packed in standard orange boxes required more time than did any of the other fruits studied. Oranges in the centers of each half of the divided orange box were cooled from 74° down to 35° after about 64 hours' storage in ware- house temperatures of 33° F. 4. Warehouse precooling is adapted to concentrated fruit areas, shipping terminals, or commercial centers, while the portable type of cooler is adapted to those areas not having warehouse facilities, and to small shipping centers or individual packers. 5. Loading of different styles of packages together in one end of the car obstructs air circulatoin and interferes with the effectiveness of car precoolers and the natural circulation of cold air from the ice bunkers. 32 University of California — Experiment Station 6. When the individual fruits of a package are wrapped and tightly placed together, the rate of cooling is retarded as contrasted with that of fruit which is unwrapped and loosely packed. The wrap- pers serve as insulators and also reduce the space for air movement, and heat is of necessity removed primarily by conduction. Open pack- ages and loose packs permit convection currents, and thus facilitate the removal of heat. 7. Small fruits cool somewhat more rapidly than large fruits. The small fruits have a larger surface per unit of volume, and this permits of more rapid reduction in temperature. 8. Packed, wrapped pears in the centers of standard boxes were cooled from 69.5° to 59.7° P with 6 hours of operation of a car pre- cooler when the car was loaded only with pears. In a mixed load, containing plum, grapes, and pears, the temperature of the pears in the center of the boxes was lowered from 67.5° to 63.5° with six hours' operation of the car precooler. 9. Grapes in Los Angeles lugs were cooled from 60.8° to 52.3° F within three hours. Additional data for cherries, apricots, peaches, tomatoes and cantaloupes are shown in table 20. 10. Wrapped, packed peaches with ice only dropped 3.4° in two hours after loading; when a car precooler was operated during the same interval of time the temperature of the peaches in another similar car dropped 8.2° F. The fruit in the car with the precooler continued to cool through the afternoon while that in the plain iced car warmed up, until after 7 hours of operation the drops were 1.8° and 15.4° respectively. 11. The importance of the initial fruit temperature as influenced by the time of day the fruit is harvested and packed is emphasized in view of the comparative difficulty in removing the heat after the fruit is packed. 12. It costs in addition to transportation charges about $105.00 for the delivery of a pre-iced car with average re-icing en route, to Chicago. The delivery of a dry car costs $21.00. To manufacture and put ice in a dry car costs about $4.50 a ton. The icing with 15,000 pounds would cost about $34.00, and this plus the initial cost of the dry car would effect a saving of about $50.00 when the car was not re-iced en route. Buii. 496] Precooling of Fresh Fruits 33 ACKNOWLEDGMENTS The authors are indebted, to certain cooperators in California, who made available fruit and equipment, as follows : The A. B. Humphrey Company, Mayhews, California. The Security Warehouse and Cold Storage Co., San Jose, Cali- fornia. The Vacaville Fruit Growers Association, Vacaville, California. Frank H. Buck & Co., Vacaville, California. The Loomis Fruit Exchange, Sacramento, California. Pomona Valley Ice and Cold Storage Co., Pomona, California. Rocky Hill Association Cold Storage and Precooling Plant, Exeter, California. The Car Precooler Service Co., Los Angeles, California. To James R. Tavernetti and F. H. Prittie for help received in making the observations and in recording data. 34 University of California — Experiment Station LITERATURE CITED i Beach, S. A., and H. J. Eustace. 1909. Cold storage for Iowa-grown apples. Iowa Agr. Exp. Sta. Bui. 108: 391-414. 1911. Studies on fruit respiration. U. S. Dept. Agr., Bur. Chem., Bui. 142: 5-40. 3 Griffiths, Ezer, and J. H. Auberry. 1928. The heat generated by fruit. Report Food Invest. Board (Great Britain) 1927:88-90. 4 McKay, A. W. 1918. Loading and transporting western 'cantaloupes. U. S. Dept. Agr. Bur. Markets Doc. 10:1-116. s Overholser, E. L., A. J. Winkler, and H. E. Jacob. 1925. Factors influencing the development of internal browning of the Yellow Newtown apple. California Agr. Exp. Sta. Bui. 370:1-40. s Powell, G. H. 1905. The transportation of fruits in refrigeration. American Soc. Refrig. Eng. Trans. 1:82-94. 7 Ramsey, H. J. 1918. Heavy loading of freight cars in the transportation of northwestern apples. U. S. Dept. Agr. Bur. Markets Doc. 13:1-23. 8 Read, F. W., et al. 1924. Refrigeration test trip. California Growers and Shippers Protective League, San Francisco, p. 1-36. 9 Ridley, V. W. 1919. • Factors in transportation of strawberries from the Ozark region. U. S. Dept. Agr. Bur. Markets Doc. 8:10. io Sttjbenrauch, A. V., and H. J. Ramsey. 1913. Bartlett pear precooling and storage investigations in Rogue River Valley. U. S. Dept. Agr. Bur. PI. Ind. Cir. 114:1-32. ii Whitehouse, W. E. 1919. Cold storage for Iowa apples. Iowa Agr. Exp. Sta. Bui. 192:179-216. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. 253. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. 263. Size Grades for Ripe Olives. 277. Sudan Grass. 279. Irrigation of Rice in California. 283. The Olive Insects of California. 304. A Study of the Effects of Freezes on Citrus in California. 310. Plum Pollination. 313. Pruning Young Deciduous Fruit Trees. 331. Phylloxera-resistant stocks. 335. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. 343. Cheese Pests and Their Control. 344. Cold Storage as an Aid to the Market- ing of Plums, a Progress Report. 346. Almond Pollination. 347. The Control of Red Spiders in Decid uons Orchards. 348. Pruning Young Olive Trees. 349. A Studv of Sidedraft and Tractor Hitches. 353. Bovine Infectious Abortion, and Asso- ciated Diseases of Cattle and New- born Calves. 354. Results of Rice Experiments in 1922. 357. A Self-Mixing Dusting Machine for Applying Dry Insecticides and Fun- gicides. 361. Preliminary Yield Tables for Second- Growth Redwood. 362. Dust and the Tractor Engine 363. The Pruning of Citrus Trees in Cali- fornia. 364. Fungicidal Dusts for the Control of Bunt. 366. Turkish Tobacco Culture, Curing, and Marketing. 367. Methods of Harvesting and Irrigation in Relation to Moldy Walnuts. 368. Bacterial Decomposition of Olives During Pickling. 369. Comparison of Woods for Butter Boxes. 370. Factors Influencing: the Development of Internal Browning of the Yellow Newtown Apple. 371. The Relative Cost of Yarding Small and Large Timber. 3 73. Pear Pollination. 374. A Survey of Orchard Practices in the Citrus Industry of Southern Cali- fornia. 380. Growth of Eucalyptus in California Plantations. 385. Pollination of the Sweet Cherry. 386. Pruning Bearing Deciduous Fruit Trees. 388. The Principles and Practice of Sun- Drying Fruit. 389. Berseem or Egyptian Clover. 390. Harvesting and Packing Grapes in California. 391. Machines for Coating Seed Wheat with Copper Carbonate Dust. 392. Fruit Juice Concentrates. 393. Crop Sequences at Davis. 394. I. Cereal Hay Production in California. II. Feeding Trials with Cereal Hays. 395. Bark Diseases of Citrus Trees in Cali- fornia. 396. The Mat Bean, Phaseolus Aconitifolius. 397. Manufacture of Roquefort Type Cheese from Goat's Milk. 400. The Utilization of Surplus Plums. 405. Citrus Culture in Central California. 406. Stationary Spray Plants in California. 407. Yield. Stand, and Volume Tables for White Fir in the California Pine Region. No. 408. 409. 410. 412. 414. 415. 416. 418. 419. 420. 421. 423. 425. 426, 427. 428. 430. 431. 432. 433. 434. 435. 436. 438. 439. 440. 444. 445. 446. 447. 448. 449. 450. 451. 452. 453. 454. Alternaria Rot of Lemons. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. Part I. Dried Orange Pulp and Raisin Pulp. Factors Influencing the Quality of Fresh Asparagus After it is Harvested. A Study of the Relative Value of Cer- tain Root Crops and Salmon Oil as Sources of Vitamin A for Poultry. Planting and Thinning Distances for Deciduous Fruit Trees. The Tractor on California Farms. Culture of the Oriental Persimmon in California. A Study of Various Rations for Fin- ishing Range Calves us Baby Beeves. Economic Aspects of the Cantaloupe Industry. Rice and Rice By-Products as Feeds for Fattening Swine. Beef Cattle Feeding Trials, 1921-24. Apricots (Series on California Crops and Prices). Apple Growing in California. Apple Pollination Studies in California. The Value of Orange Pulp for Milk Production. The Relation of Maturity of California Plums to Shipping and Dessert Quality. Range Grasses in California. Raisin By-Products and Bean Sci-een- ings as Feeds for Fattening Lambs. Some Economic Problems Involved in the Pooling of Fruit. Power Requirements of Electrically Driven Dairy Manufacturing Equip- ment. Investigations on the Use of Fruits in Ice Cream and Ices. The Problem of Securing Closer Rela- tionship between Agricultural Devel- opment and Irrigation Construction. I. The Kadota Fig. II. The Kadota Fig Products. Grafting Affinities with Special Refer- ence to Plums. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. II. Dried Pineapple Pulp, Dried Lemon Pulp, and Dried Olive Pulp. The Feeding Value of Raisins and Dairy By-Products for Growing and Fattening Swine. Series on California Crops and Prices: Beans. Economic Aspects of the Apple In- dustry. The Asparagus Industry in California. A Method of Determining the Clean Weights of Individual Fleeces of Wool. Farmers' Purchase Agreement for Deep Well Pumps. Economic Aspects of the Watermelon Industry. Irrigation Investigations with Field Crops at Davis, and at Delhi, Cali- fornia, 1909-1925. Studies Preliminary to the Establish- ment of a Series of Fertilizer Trials in a Bearing Citrus Grove. Economic Aspects of the Pear Industry. Series on California Crops and Prices: Almonds. Rice Experiments in Sacramento Val- ley, 1922-1927. BULLETINS— (Continued) No. No. 455. Reclamation of the Fresno Type of 465. Black-Alkali Soil. 466. Yield, Stand and Volume Tables for Red Fir in California. 467. Factors Influencing Percentage Calf 468. Crop in Range Herds. Economic Aspects of the Fresh Plum 469. Industry. 470. 460. Series on California Crops and Prices: Lemons. 471. 461. Series on California Crops and Prices: Economic Aspects of the Beef Cattle 474. Industry. Prune Supply and Price Situation. Drainage in the Sacramento Valley 475. Rice Fields. 456. 458. 459. 462. 464. Curly Top Symptoms of the Sugar Beet. The Continuous Can Washer for Dairy Plants. Oat Varieties in California. Sterilization of Dairy Utensils with Humidified Hot Air. The Solar Heater. Maturity Standards for Harvesting Bartlett Pears for Eastern Shipment. The Use of Sulfur Dioxide in Shipping Grapes. Factors Affecting the Cost of Tractor Logging in the California Pine Region. Walnut Supply and Price Situation. CIRCULARS No. 115. Grafting Vinifera Vineyards. 117. The Selection and Cost of a Small Pumping Plant. 127. House Fumigation. 129. The Control of Citrus Insects. 164. Small Fruit Culture in California. 166. The County Farm Bureau. 178. The Packing of Apples in California. 203. Peat as a Manure Substitute. 212. Salvaging Rain-Damaged Prunes. 230. Testing Milk. Cream, and Skim Milk for Butterfat. 232. Harvesting and Handling California Cherries for Eastern Shipment. 239. Harvesting and Handling Apricots and Plums for Eastern Shipment. 240. Harvesting and Handling California Pears for Eastern Shipment. 241. Harvesting and Handling California Peaches for Eastern Shipment. 243. Marmalade Juice and Jelly Juice from Citrus Fruits. 244. Central Wire Bracing for Fruit Trees. 245. Vine Pruning Systems. 248. Some Common Errors in Vine Pruning and Their Remedies. 249. Replacing Missing Vines. 250. Measurement of Irrigation Water on the Farm. 253. Vineyard Plans. 255. Leguminous Plants as Organic Ferti- lizers in California Agriculture. 257. The Small-Seeded Horse Bean (Vicia faba var. minor). 258. Thinning Deciduous Fruits. 259. Pear By-Products. 261. Sewing Grain Sacks. 262. Cabbage Production in California. 263. Tomato Production in California. 265. Plant Disease and Pest Control. 266. Analyzing the Citrus Orchard by Means of Simple Tree Records. No. 269. 270. 276. 277. 278. 279 282. 284. 287. 288. 289. 290. 292. 294. 295. 296. 298. 300. 301. 302. 304. 305. 307. 308. 309. 310. 311. 312. 313. 314. 315. An Orchard Brush Burner. A Farm Septic Tank. Home Canning. Head, Cane, and Cordon Pruning of Vines. Olive Pickling in Mediterranean Countries. The Preparation and Refining of Olive Oil in Southern Europe. Prevention of Insect Attack on Stored Grain. The Almond in California. Potato Production in California. Phylloxera Resistant Vineyards. Oak Fungus in Orchard Trees. The Tangier Pea. Alkali Soils. Propagation of Deciduous Fruits. Growing Head Lettuce in California. Control of the California Ground Squirrel. Possibilities and Limitations of Coop- erative Marketing. Coccidiosis of Chickens. Buckeye Poisoning of the Honey Bee. The Sugar Beet in California. Drainage on the Farm. Liming the Soil. American Foulbrood and Its Control. Cantaloupe Production in California. Fruit Tree and Orchard Judging. The Operation of the Bacteriological Laboratory for Dairy Plants. The Improvement of Quality in Figs. Principles Governing the Choice, Oper- ation and Care of Small Irrigation Pumping Plants. Fruit Juices and Fruit Juice Beverages. Termites and Termite Damage. The Mediterranean and Other Fruit Flies. 15m-6,'30