UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

PRECOOLING AND SHIPPING
CALIFORNIA ASPARAGUS

W. T. PENTZER, R. L. PERRY, G. C. HANNA,
J. S. WIANT, AND C. E. ASBURY

Results of a cooperative investigation conducted by the United States

Department of Agriculture Bureau of Plant Industry and the

California Agricultural Experiment Station

BULLETIN 600

APRIL, 1936

UNIVERSITY OF CALIFORNIA
BERKELEY, CALIFORNIA

CONTENTS

PAGE

Introduction 3

Precooling 5

Reasons for precooling 6

Principles of precooling 7

Precooling tests with portable inside fans 8

Description of car-precooling equipment used 8

Fan capacities under car-precooling conditions 9

Resistance encountered in carloads of asparagus 10

Cooling rate as affected by air volume 12

Method of measuring temperatures in precooling tests 12

Precooling test with portable brine radiator and fans 15

Precooling in tanks filled with ice water 16

Discussion and summary of precooling tests 18

Effect of loading method on cooling 20

Importance of air volume 20

Importance of air distribution 21

Value of low air temperatures in rapid cooling 21

Temperatures of various positions in the load and average temperature of

load 22

Shipping tests 24

Standard versus modified refrigeration 25

Loading 7 rows wide, 4 and 5 layers high versus 8 rows wide, 4 layers high 26
Carrying quality of different varieties; loose pack, unwrapped bunches and

wrapped bunches; and asparagus grown on peat soil and sediment soil. . 28

Ice-water dipping versus portable-fan precooling 30

Cellophane wraps and caps for the bunches 31

Carrying quality of long-green and white-butt asparagus as affected by

delay in removal from the field after cutting 32

Discussion and summary of shipping tests 36

Respiration of asparagus 39

Respiration studies, 1933 season 39

Respiration studies, 1934 season 42

General summary and conclusions 43

Acknowledgments 45

PRECOOLINGAND SHIPPING
CALIFORNIA ASPARAGUS 1

W. T. PENTZEE, 2 E. L. PEEEY, 3 G. C. HANNA, 4
J. S. WTANT, 5 and C. E. ASBUEY 6

INTRODUCTION

The asparagus growers of California rely upon two outlets for their
production : the cannery and fresh shipment to eastern and local mar-
kets. During the five-year period 1929 to 1933, according to estimates of
the Federal-State Market News Service/ the average annual acreage for
canneries amounted to 44,380 acres; for fresh shipment 20,770 acres.
Carload shipments of fresh asparagus for this period totaled 11,480 cars,
an average per year of 2,296 carloads. The shipments of fresh asparagus
represent a large investment, not only in the asparagus itself but like-
wise in costs of harvesting, grading, packing, loading, freight, and re-
frigeration by the time it reaches the East. Failure of the asparagus to
arrive on the market in good, salable condition would therefore entail
serious losses to the industry and jeopardize an important outlet for
almost one-third of the production. A condition approaching this existed
in 1930, 1931, and 1932, when serious losses were experienced in many
shipments as a result of mold growth on the asparagus in transit. Since
no experimental evidence was available to establish the cause for the
excessive mold growth, the University of California was requested by
representatives of the asparagus industry to investigate the handling
and shipping of asparagus. These investigations were conducted cooper-
atively by the University of California and the United States Depart-
ment of Agriculture.

Among explanations offered by shippers for the poor condition of the

1 Eeceived for publication January 27, 1936.

2 Physiologist, United States Department of Agriculture Bureau of Plant Industry.

3 Assistant Professor of Agricultural Engineering, Assistant Engineer in the
Experiment Station.

4 Associate in the Experiment Station, Division of Truck Crops.

5 Associate Pathologist, United States Department of Agriculture Bureau of Plant
Industry.

8 Junior Pomologist, United States Department of Agriculture Bureau of Plant
Industry.

7 Cox, W. F., and W. L. Jackson. Marketing California asparagus — 1934. U. S.
Dept. Agr. Bur. Agr. Econ. and California Dept. Agr. Bur. Markets, p. 1-29. 1934.
(Mimeo.)

[3]

4 University of California — Experiment Station

asparagus on arrival were the kind of soil on which the asparagus was
grown ; the length of time it was left in the field before being picked up
and packed ; the age, or length of green area, of the spear ; and tempera-
tures existing in transit. These factors and their bearing on the problem
were all considered. The transit-temperature question, however, ap-
peared to be the most significant. The organisms responsible for the mold
growth were identified at destination markets by pathologists of the
United States Department of Agriculture as species of Fusarium. Since
this mold can be checked by temperatures of 40° Fahrenheit or less, its

Mo/7.

Tuesday

Wednesday

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1
erecoo/ed

' <m A

^ecoo/

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Fig. 1. — Transit-temperature records for nonprecooled and precooled asparagus
cars, shipped by standard refrigeration. Loaded at Valdez, California, March 21,
1932. Shipped to New York and Boston.

excessive growth in certain carloads of asparagus was fairly good evi-
dence of transit temperatures considerably higher than 40° F in the top
layers, where the mold was most prevalent.

Allen and McKinnon, 8 conducting a preliminary precooling and ship-
ping test in March, 1932, found that the temperatures in a precooled
car, as recorded by a Ryan thermometer placed between the crates, aver-
aged 45° F for the first day and 47° F the first 4 days as compared with
corresponding temperatures in a nonprecooled car of 61° and 56° F.
The temperature records in these two cars are shown in figure 1. During
the precooling period of 5% hours the asparagus was cooled from 62° to
43° F ; and, as indicated, this amount of cooling produced car tempera-
tures 16° lower the first day and 9° lower for a 4-day period than in a
similar, nonprecooled car.

Judging by these results, if warm asparagus is loaded into cars and
not precooled, high temperatures favorable to mold growth will pre-
vail for several days, whereas thorough precooling might be the solution
to the mold problem. In these investigations, therefore, precooling re-
ceived particular attention. Precooling and shipping tests were made
during the latter part of the 1933 and 1934 seasons, when high field and
transit temperatures were to be expected. Records were obtained on (1)
precooling of asparagus by means of portable or semiportable car pre-
coolers ; (2) precooling during the packing process in tanks of ice water ;

8 Allen, F. W., and L. E. McKinnon, unpublished data.

Bul. 600 J PRECOOLING AND SHIPPING ASPARAGUS 5

(3) temperatures in transit after precooling by various methods; (4)
condition on arrival as affected by the amount of green in the spear ;
(5) field handling, and method of packing and shipping; and (6) res-
piration at transit and storage temperatures.

PRECOOLING

Though the precooling of some fruits has been an established practice
for many years, few vegetable shipments from California, until recently,
have been precooled. Many vegetables, such as lettuce, peas, asparagus,
and celery, are fully as perishable as fruits that are commonly cooled
and are greatly benefited by the removal of "field" heat as soon as possi-
ble after harvesting. Most of the perishable vegetables are, however,
heavily iced while being packed and loaded in the car. Ice is often used
inside the crate or hamper, between the layers in the load, in pigeonholes
throughout the load, and on top of the load. Not uncommonly 10,000 to
15,000 pounds of ice are used in the packages, the body of the load be-
tween packages, and on top of the load. This method of icing of course
cools the vegetables very rapidly and produces low transit temperatures
if enough ice is supplied. Since, however, this method of shipping wets
the commodity and package, it is not used for some products, including
asparagus. The removal of heat by precooling has therefore been more
acceptable.

Until recent years few facilities, other than precooling warehouses,
have been available for the precooling of vegetables and fruits. The com-
modity was trucked from the field or packing-house to the precooling
rooms and then loaded into the cars after cooling. Some producing dis-
tricts were distant from precooling plants, and the extra handling and
delay discouraged the practice. In the last few years, however, portable
precooling equipment has been developed for use in refrigerator cars,
so that wherever cars are loaded and ice and electric current are avail-
able, cooling is possible. Recently developed equipment consists of com-
pressors, evaporators, condensers, and fans, all mounted on a truck
chassis and driven by a power take-off from the truck engine, so that
precooling can now be done even where ice and power are difficult to
obtain.

Much interest was awakened in precooling and precooling equipment
by the granting of railroad refrigeration rates for one re-icing in transit
in 1932 (rule 247). These rates were appreciably lower than those for
standard refrigeration service, which provides for 10 to 12 re-icings. As
some commodities, if thoroughly precooled, could be shipped with one
re-icing, the saving in transit-refrigeration costs more than paid for pre-

6 University of California — Experiment Station

cooling. In cool weather such as prevails when early asparagus ship-
ments are made, some precooled cars are shipped with no re-icing in
transit nnder "limited refrigeration" at still lower rates. .

REASONS FOE, PRECOOLING

The practical reasons for precooling in many cases are, first, to remove
the field heat from the commodity so that transit temperatures will be
lower during the first part of the trip and, second, to refrigerate the load
sufficiently so that it will require less ice in transit. By cooling the aspar-
agus as soon as possible, several benefits are obtained that may not be
apparent to the shipper or the receiver. If temperatures in transit are
sufficiently low, protection from spoilage organisms is afforded, as men-
tioned above.

This benefit is usually self-evident. Low temperatures likewise pre-
serve the quality of the asparagus. As Bisson, Jones, and Robbins 9 have
shown, the deterioration processes, as evidenced by reduction in sugar
and increase in fiber, begin immediately after cutting. These processes
were greatly retarded, although not suspended, by holding the asparagus
at 33° F. The changes proceeded in direct proportion to the temperature
of the asparagus and were most rapid during the first 24 hours after
cutting. A temperature of 41° was much superior to 56° and 77° in
preserving quality, though not equal to 33° F. Cooling the asparagus
as soon as possible after cutting is therefore a good practice from the
viewpoint of preserving quality.

The loss in sugar mentioned in the previous paragraph takes place
through respiration, a process common to all living things. In respiration
the sugar and some other carbon compounds are broken down, carbon
dioxide and water are given off, and energy in the form of heat is re-
leased. Respiration goes on in direct proportion to the temperature of
the asparagus within the range encountered in transit and storage, as
shown in studies made during these investigations. Heating, sometimes
observed in closely packed field boxes of asparagus, is from respiration.
It takes place in the refrigerator car, but the rate of heat released
will depend on the temperature of the asparagus. Another reason for
cooling, therefore, is to keep the heat of respiration low. This is particu-
larly important with asparagus, for its respiration rate and heat-evolv-
ing capacity are extremely high. According to Benoy's 10 studies on the
respiration of vegetables at 30° C (86° F), asparagus respired at the

9 Bisson, C. S., H. A. Jones, and W. W. Robbins. Factors influencing the quality of
fresh asparagus after it is harvested. California Agr. Exp. Sta. Bui. 410:1-27. 1926.
(Out of print.)

10 Benoy, Marjorie P. The refrigeration factor in the deterioration of fresh vege-
tables at room temperature. Jour. Agr. Research 39:75-80. 1929.

BUL. 600] PRECOOLING AND SHIPPING ASPARAGUS 7

highest rate, followed by lettuce, green beans, okra, green onion, carrot,
tomato, beet, green mango, and red pimiento, in descending order.

PRINCIPLES OF PRECOOLING

In precooling asparagus much refrigeration is needed in addition to that
required for removing the field heat from the asparagus itself. The in-
terior of the car and all material necessary to pack and load the com-
modity must be cooled. Refrigeration is lost through cracks around doors
and hatches and even through walls, floor, and roof. The motors of the
fans give off heat, which adds to the refrigeration needed. The asparagus
itself, through respiration, is releasing heat that must be removed during
the cooling process. The total refrigeration needed to provide for each
of these requirements can be estimated. Allen and McKinnon, 11 in dis-
cussing the precooling of fruit, show that the refrigeration actually
required to cool a carload of pears proved to be very close to the estimated
amount.

Of all the refrigeration requirements, that needed to remove the field
heat is the largest. This can be estimated if the weight of the carload and
the specific heat or heat capacity of the commodity are known. About
20,000 pounds of asparagus are loaded in a car ; and the specific heat,
calculated from the moisture content of about 93 per cent, is 0.94. Siebel's
formula, as adapted from Rose, Wright, and Whiteman 12 is

8= (1-0.2) a + 0.2

where S, = unit heat capacity of substance ex-

pressed in B.t.u. per lb. °F.

a, = fraction of water in substance

0.2, = assumed value of unit heat capacity

of dry matter in substance expressed
in B.t.u. per 16° F.

The heat to be removed from the asparagus load to reduce it from 70° to
40°, a reduction of 30°, would then be 20,000 x 0.94 x 30 or 564,000 B.t.u.
A British thermal unit (B.t.u.) is the quantity of heat required to raise
the temperature of 1 pound of water 1° F.

With asparagus, the refrigeration requirement for the heat of respira-
tion is large. According to these investigations, the heat evolved during
precooling from 70° to 40° F in a period of 12 hours would approximate
297,000 B.t.u. This figure is obtained by assuming that the heat liberated
is from the combustion or respiration of hexose sugars. The ice required
to supply refrigeration for these two sources of heat, together with other

u Allen, F. W., and L. E. McKinnon. Precooling investigations with deciduous
fruit. California Agr. Exp. Sta. Bui. 590:11-14. 1935.

12 Eose, Dean H., E. S. Wright, and T. M. Whiteman. The commercial storage of
fruits, vegetables, and florists' stocks. U. S. Dept. Agr. Cir. 278:8. 1933.

8 University of California — Experiment Station

requirements for a carload of asparagus precooled from 70° to 40° F in
12 hours with fans, is as follows : Pounds

of ice

Removal of field heat from asparagus from 70° to 40° F 3,917

Removal of heat of respiration 2,063

Cooling of crates, moss, etc. : 608 crates estimated as

4 lbs. per crate, specific heat of 0.42 (wood) 214

Heat from 2 motors of fans — ^ hp. each 325

Total 6,519

Heat losses through the car are not estimated, since they would vary
with the condition, amount, and type of insulation in the car and the
tightness of the car and its doors and hatches. In actual cooling tests in
which the asparagus was cooled approximately 30° F in 12 hours, about
7,000 to 7,500 pounds of ice were melted.

Other factors affecting the amount and rate of cooling are the method
of loading the packages in the car or room as it affects circulation of air
around the commodity ; the shape of the commodity and the surface ex-
posed in relation to its weight ; and the cooling medium and its velocity
and temperature.

PRECOOLING TESTS WITH PORTABLE INSIDE FANS

Description of Car -Precooling Equipment Used. — The precooling equip-
ment most commonly used was a portable type consisting of fans
mounted on frames which were set in metal plates that cover the top
screened opening in the bunkers (fig. 2).

One fan was mounted in each end of the car to pull air from the floor,
through the lower screen of the bunker, up through the ice and to blow
the cooled air out over the load. The fans, directly connected with either
14 or Y2 horsepower motors, were usually directed downward so the air
stream would strike the load about halfway between bunker and door-
way. Salt added to the ice resulted in low-temperature ice-salt mixtures
in the bunkers and lower air-blast temperatures. The fans were started
as soon as the cars were loaded, after the salt had been added and the ice
in the bunkers tamped with bars ("barred down") to fill any large cavi-
ties. By some operators the ice was replenished during the precooling
period. The fans were permitted to run until the cars were switched or
until desired temperatures (about 40° F) had been reached — usually in
10 to 12 hours. Operators generally take the temperatures in the aspara-
gus crates at the doorway and several tiers back from the doorway, and
sometimes the air temperature at the fan and at the doorway. The ability
of this equipment to cool the commodity depends, of course, upon the

Bul. 600 J

Precooling and Shipping Asparagus

air delivered by the fans and upon the transfer of refrigeration from
t lie ice to the asparagus. To learn something about the fans used in the
cooling investigations, tests were made of their capacities and of the
effect of air volume on cooling rate. 13

Fan Capacities Under Car ^Precooling Conditions. — Air must be de-
livered by the precooling fan at a pressure sufficient to overcome the

Fig. 2. — Portable-fan precooler in place at top of bunker duet.

frictional resistance encountered in the path through the load, false
floor, return duct, bulkhead openings, and ice bunker. Capacities of fans
depend upon the static pressure (defined as pressure exerted by a fluid
upon a plane parallel to its direction of motion) against which the air is
delivered. The static pressures developed at different capacities by the
fans used in the precooling tests were measured by the apparatus shown
in figure 3. The results are shown in figure 4.

The capacity of the 1,740-r.p.m., 20-inch diameter, 4-blade fan was
found to be 3,900 cubic feet per minute at no static pressure (free air),
dropping to 2,450 cubic feet per minute at 0.2 inches of water-static
pressure. The 3,450-r.p.m., 20-inch diameter, 2-blade fan delivered 4,400

13 These tests and those on cooling rates in ice water were conducted at the
Agricultural Engineering Laboratory, University of California, Davis, California.

University of California — Experiment Station

cubic feet per minute at no static pressure, and 2,900 cubic feet per
minute at a static pressure of 0.27 inches of water.

Resistance Encountered in Carloads of Asparagus. — The resistances
encountered in the cars ranged from 0.16 to 0.20 inches of water for the

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-Precooler fan characteristics and load resistance.

sooo

4-blade, 1,740-r.p.m. fan, and from 0.21 to 0.27 inches of water for the
2-blade, 3,450-r.p.m. fan (fig. 4). The operating capacity of the first fan
thus ranged from 2,450 to 2,750 cubic feet per minute, that of the second
fan from 2,900 to 3,200 cubic feet per minute, varying with the loading
arrangement of the car and the resistance offered by the ice bunker.

Laboratory tests of resistance to vertical air flow through stacks of
asparagus crates were made in a wind tunnel (fig. 5) arranged to

Bul. 600]

Precooling and Shipping Asparagus

Fig. 5. — Laboratory apparatus for determining resistance to air flow through
crates of asparagus, and relation between air volume and cooling rate.

12 University of California — Experiment Station

simulate the spacing of a car loaded 7 or 8 rows wide. For the equivalent
of a 19-tier load, 7 rows wide and 5 layers high, the resistance encoun-
tered by air moving vertically downward through the stack of crates and
slatted floor was

A =°- 00058 (rM

where h, inches of water = static pressure difference, and

Q, cubic feet per minute = air volume for both ends of the car.

This equals a resistance of 0.009 inches of water for 4,000 cubic feet per
minute (2,000 cubic feet per minute at each end of the car) . Since, how-
ever, not all the air delivered by the fan passes through the load, some
escaping through the break in the load at the brace, this calculation was
not based on the total volume of air delivered by the fan.

For the equivalent of a 19-tier load, 8 rows wide and 4 layers high, the
relation was

/l = 00058 (^J

This equals a resistance of 0.09 inches of water for 4,000 cubic feet per
minute.

These expressions do not include the resistance offered by the bunker

nor the additional resistance of the air movement in other directions.

Air movement through the load is assisted by the velocity of the air

stream from the fans located at the bulkhead opening. The difference

in air flow between the two methods of loading is thus much less than

would be indicated by the simple laboratory tests.

Cooling Rate as Affected by Air Volume. — The relation between air
volume and cooling rate was also studied in the wind tunnel, with ther-
mocouples inserted into the spears and with the resistance thermometers.
Tests were made with 4-high tiers of crates spaced to duplicate a load 8
rows wide. Cooling was improved when the air volume was increased
from 17.6 to 26 cubic feet per minute per tier, with little if any beitefit
from a further increase to 36. About 30 cubic feet per minute per tier
of 4 crates is equal to 4,600 cubic feet per minute through the load.
Lloyd, 14 in tests with apples packed in lined bushel baskets, found that
air movement if rapid enough reduced the cooling time as compared with
still air or lower velocities. In these tests with a relatively tight package,
air velocities of 156.2 feet per minute were necessary to increase cooling.

Method of Measuring Temperatures in Precooling Tests. — During the
seasons of 1933-1935, detailed precooling records were obtained on thir-

14 Lloyd, T. W., and S. W. Decker. Factors influencing the refrigeration of packages
of apples. Illinois Agr. Exp. Sta. Bui. 410:30. 1934.

Bul. 600]

Precooling and Shipping Asparagus

teen cars. Temperature records were taken in the crates of asparagus in
various parts of the car by means of resistance thermometers that could
be read from outside the car. Air temperatures were taken in the same
way at the fan, at the lower bulkhead opening (designated as air re-
turn ) , and at the doorway in the head space above the crates of aspara-
gus. Temperatures of asparagus in nine locations in the car were usually
taken (fig. 6, pulp temperatures). Only temperatures at these general

xsss^sss^

Fig. 6. — Diagram of car showing positions of thermometers for precooling tests.

locations were considered in computing the average temperatures of the
precooled cars reported in table 1. Since all temperatures were taken
in the quarter-length stacks in car E, that car was omitted from the
summary of the precooling studies.

The thermometers were distributed through the load from top to
bottom, from bunker to doorway, and from side to side in positions that
would give a fair average temperature for one end of the car. Tempera-
ture records for one end have been found to approximate closely those
obtained in the other half, as shown for cars L and N in table 1. These
thermometers have a sensitive element consisting of a fine coil of nickel
wire enclosed by a protecting metal sheath about the size of a lead pencil
and 3 inches long. They were inserted at an an angle into the side bunches
in the crates, piercing the paper wrap and some of the spears.

To determine whether the thermometers indicated the asparagus tem-
perature accurately, supplementary observations were made with cop-
per-constantan thermocouples inserted into individual spears in several
crates. The results of a typical test (fig. 7) on a crate in layer 2, row 7,
stack 4 of car M show that the resistance thermometer represents the
side-bunch temperatures fairly well. The center bunches cool more
slowly than the side bunches, lagging as much as 6° F at the end of pre-

University of California — Experiment Station

4 6

r//77e f /?ot/rs

Fig. 7. — Temperatures of asparagus spears during precooling
with fan-driven cold air.

^ so

Average J ivar/nest po/fits //s£ a/xt Sat/ /oyer, yc/ar/er /e/7g£/>)

Average /oarf

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Z700* /ce
JJS *so/£ /OO *sa/t

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Fig. 8. — Air and asparagus temperatures in car M, a typical portable fan-cooled car

Bul. 600J

Precooling and Shipping Asparagus

cooling. In all but the top layer the center bunches, which comprise 25
to 27 per cent of the load, are not exposed to direct air movements. The
average asparagus temperature would be 1° to 1.5° higher than the aver-
age of the resistance-thermometer readings given in table 1.
70

Average of J po/'/its war/nest at f/a/s/>.
Average of toad.

flveraae of J cao/est po/rfs.

J-

/?/7a / co/npressor started.

SBrin e-sapp/y temper atc/re

Defrost

1 c

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O £ 4 6 S

r/me precoof/r??, fioc/rs

Fig. 9. — Air and asparagus temperatures in a car cooled by a portable
brine-cooled radiator placed at the doorway.

A cooling record for M, a typical car (fig. 8) , shows the prompt reduc-
tion of the air-blast temperature and the wide difference in the cooling
rate that usually occurs at top and bottom layers. All the cars were
cooled during the late afternoon and night, when outside temperatures
ranged from about 70° to 40° F.

PRECOOLING TEST WITH PORTABLE BRINE RADIATOR AND FANS

Although several types of units for precooling loaded cars with refriger-
ation supplied by compressors and brine systems have been developed,
few of these have been used for asparagus. A unit introduced for this
purpose consisted of a set of four directly connected vertical-shaft pro-
peller fans which draw air up through a finned-coil section placed across
the load at the doorway and blow the cooled air over the lading. The car
is cooled on a siding at a refrigeration plant. Brine hoses brought out
through a false door in the car connect the finned-coil section to the brine
supply of the plant. A test made with this apparatus during the 1935
season is reported below and is discussed in the summary.

Car N was loaded at Antioch on April 16, 1935, with asparagus packed

16 University of California — Experiment Station

the previous evening. The load was 4 layers high, being 8 rows wide al one
end and 7 at the other. Loading was completed at 3 :35 p.m., with a tem-
perature average of 60.4° F, which had dropped to 57° P when the ear
reached the warehouse at Stockton for precooling. The precooling unit
consisted of a 2-inch, 5-horsepower centrifugal pump delivering brine at
16.5° to 21° F to a finned-coil section 18 inches by 8 feet in size, placed
in the car on the brace. Air was sucked through the load and the radiator
by four vertical-shaft, 6-blade, 16-inch diameter fans driven by %-horse-
power motors, and was blown toward the car ceiling. In operation, after
each 60 minutes of cooling, the brine was shut off for 10 minutes to allow
defrosting. Although some frost that melted may have evaporated, most
of it dripped to the floor. The temperature records (fig. 9) show that the
difference in temperature between the asparagus and the air, and the
temperature rise of the air passing through the load, remained about
constant, the average air temperature dropping with that of the aspara-
gus. Dry and wet-bulb temperatures taken with a hygrodeik placed in
the fan blast showed 2° to 3° differences except during defrosting, cor-
responding to a dew point of 32° to 33° F at the fan discharge during the
last 8 hours of precooling.

PRECOOLING IN TANKS FILLED WITH ICE WATER

As was mentioned in discussing the reasons for precooling, the more
rapidly the heat is removed from the asparagus after cutting the better
will its quality be preserved and the less heat will be evolved by the
asparagus. One of the most rapid methods of cooling is to submerge in
ice water. As one step in the preparation for packing, the asparagus is
freshened by placing it in a shallow tank of water. Presumably cooling
could be effected quickly by making the tank deeper and circulating ice
water through it.

To secure data for the design for an ice-water cooling system, labora-
tory tests were made on the cooling rates of immersed asparagus bunches.
Thermocouples for measuring temperatures were inserted into center
and outside spears of five bunches representing four size-grades. These
were placed in a wire basket that fitted a channel 5% inches wide,
through which water in contact with crushed ice could be circulated.
After a cooling test, warm water was run through the channel, and the
test was repeated at a different circulation rate. The curves shown in
figure 10 are for a rate of 3 gallons per minute, which in practice had to
be reduced to 2 gallons per minute to avoid tipping over the bunches.

In the first packing-shed experiment the water was recirculated from
the freshening tank to an ice tank where, being sprayed over chunks of
ice, it was cooled to temperatures ranging from 36° to 40° F. The bunches

Bul. 600]

Precooling and Shipping Asparagus

of asparagus were about two-thirds submerged in the water, butts down,
for about 10 minutes, then taken from the tank, packed, and loaded in
the car immediately. The load was covered with a canvas to retard warm-
ing during the loading, which required several hours. The average aspar-
agus temperature when loaded was 50.1° F as compared with 56.5° F in
a companion car, not cooled. The net result of cooling 10 minutes in ice
water was a temperature reduction of 6.4° F. The car loaded with aspara-

1 \

Po//t£

sy/r?6o/

Pos/hon
of spear

3i//7C/f wt.

/£>. oz.

tf(//7?ber
ofspeers

•
+ '

ovts/de
center
ot/ts/de
eerier
center

2 /4

3 4
3 4
3

+. ^^»

^""**"-+.».

— — +

6 S

77/7? e Si/S/ner&et/j a»//w£es

./<?

Fig. 10. — Temperatures of asparagus spears during cooling with water at
32° F at a volume of 3 gallons per minute for 5 bunches.

gus cooled in ice water was then precooled with fans for 8 hours in the
ordinary way. At the end of this period the asparagus temperature
averaged 38.8° F as compared with an average asparagus temperature
of 40.5° F in a companion car similarly precooled for 11 hours but not
cooled in ice water.

In the second test, an insulated ice-melting tank for cooling was ob-
tained through the cooperation of interested agencies. The asparagus
was left in the freshening tank about 12 minutes, the bunches being sub-
merged about three-fourths their length, butts down. The ice water en-
tered the freshening tank at temperatures of 33° to 34° F and left it at
about 40° F. The asparagus was cooled in this tank from about 62° F to
40° F, or 22°, a much better result than in the first test. By the time the
car was loaded, the average asparagus temperature was 44.7° F. In 5
hours' precooling with fans the asparagus in this car was cooled to 39.1°
F, whereas in the companion car cooled with fans only 40.8° F was
reached in 11% hours.

As these preliminary results indicate, this method of cooling has ad-

18 University of California — Experiment Station

vantages over the present one of blowing cold air through the load. The
principal advantage is the more rapid heat transfer ; but the freshening
effect of the cold water should have some value. Asparagus cooled by
standing in ice water weighed about 1 pound more per crate than that
handled in the usual way, probably because of the water which it ab-
sorbed or carried with it. This additional moisture should assist in pre-
serving its freshness.

Inspection on arrival did not reveal that the ice-water treatment had
any deleterious effect, contrary to the general belief that wetting the
spears, particularly the tips, was harmful. Several crates which had been
entirely submerged, also arrived in good condition.

For ice-water cooling in a packing house, much of the handwork re-
quired in the experimental setup could be eliminated by special equip-
ment to convey the asparagus through cooling tanks or sprays to the
packers. This type of equipment is already in use in precooling celery
and certain other leafy vegetables.

DISCUSSION AND SUMMARY OF PRECOOLING TESTS

The precooling tests are summarized in table 1. These tests include 9 with
portable fans, 1 with brine coils, and 2 with ice water. Cars A, B, and C
were loaded 7 crates wide ; car N was loaded 8 wide in one end and 7
wide in the other end. All the other cars were loaded 8 crates wide. From
loading temperatures occasionally as high as 72° F, portable-fan equip-
ment brought the asparagus to final temperatures ranging between 37°
and 49° F, in 11 to 13 hours. With the brine precooler, temperature was
not reduced so quickly. Precooling with ice water was most rapid, the
asparagus temperature being reduced as much as 22° F in 12 minutes.
In cooling by air, the rate of temperature drop depends upon the com-
modity to be cooled ; the method of packing and loading ; the volume,
velocity, and distribution of the air ; and the air and asparagus tempera-
ture. To eliminate the variations in initial asparagus temperature and
air temperature when comparing the effect of car loading or the number
and type of fans, a cooling coefficient was determined for each test —
namely, the rate of temperature drop (degrees F per hour) divided by
the average difference between asparagus and air-blast temperatures. In
computing this coefficient, the data obtained in the first hour of cooling
were not included because of the rapid change in air temperature which
occurs then. The average rate of temperature drop was obtained for the
remainder of the run by subtracting the final average asparagus tem-
perature from that at the end of the first hour and dividing by the
elapsed time. (Note that the average rate of temperature drop given in
table 1 is not the one used for calculating the cooling coefficient.) The

Bul. GOOj

Precooling and Shipping Asparagus

differences between average asparagus temperature and air-blast tem-
perature for each hour were added and divided by the number of ob-
servations. The rate of temperature drop after the first hour was then

TABLE 1

Summary of Precooling Tests

Car

L "A" end
L "B" end

N "A" end
N "B" end

Precooling
time

hours

ioy 2

13
13
13
11

1/6
11

1/5
13
12
12
12
10
10

Average asparagus
temperature

Start

72.6
70 9
59 9
63 3
56.5
56 5
60.7
62
72.7
69.8
69 6
69.2

56 6

57 3

Finish

49
44

42 1

43
40 5
50.lt
41.2

40
41.4
38.2
37.0
38 6

41 4
43 6

Asparagus temperature drop

Total

23 6
26.9
17.8
20.3
16
6.4
19.5
22.0
31.3
31.6
32.6
30.6
15 2
13 .7

Rate
per hour

°F

2.2
2 1
14
1.6
15

1.8

2.4
2.6
2.7
2.6
15
14

Cooling
coefficient*

F per hour
per ° F

0.09

12
0.11
0.17
13
14
09

Car

L "A" end
L "B" end

N "A" end
N "B" end

Average air

temperature

at fan after

first hour

o p

34 3
33.0
36.7
36.8
34.6

31 2

34 9

32
31 3
34.6 \
34.6 J

Salt and ice supplied

Salt

pounds
450
450
250
250
250
Water
500
Water
597
550

475
Brine

Ice

pounds

4,200

cooled

cooled
3,680
2,950

2,760
cooled

Fan designation

Number

fans

Horse-
power
each

X4,

hi.

Number

blades

Revolutions

per

minute

1,740
1,740
1,740
1,740
1,740

1,740

1,740
3,450

3,450
3,500

* The "cooling coefficient" is the rate of temperature drop in degrees F per hour, divided by the dif-
ference between the average asparagus and the air-blast temperatures.

t Temperature of asparagus after being loaded in car about 4 hours after cooling started.

divided by the average temperature difference thus obtained, to give the
ratio called the "cooling coefficient." If heat due to respiration, leakage
through car walls and crevices, motors, and air friction did not affect per-
formance, the temperature-difference-time curve would be a straight
line on semilogarithmic cross-section paper, whose slope would be the

20 University of California — Experiment Station

cooling coefficient. Evidently, where the air circulation and the method
of loading' produce an effective transfer of heat from asparagus to ice, a
high cooling coefficient will be shown. As an example of the application
of this coefficient, the "B" end of car L (table 1) showed the highest
value of any. Its rate of drop was higher than for any other car, although
the initial temperature was lower than some and the air blast not so low
as in some others. Again, the rapid rate of drop in car K might suggest
much more effective performance of the precooling units than in car P.
More careful scrutiny discloses that the air-blast temperatures being
about the same, the rapid drop was made possible by the high initial
asparagus temperature, and the coefficient for the two cars differed only
slightly.

Effect of Loading Method on Cooling. — Contrary to expectation, the
cars loaded 7 rows wide did not always show more rapid cooling than
those with the more closely spaced 8-row load, as can be seen by com-
paring cars D and K (8 wide) respectively with C and A (7 wide) . Car D
showed a slightly lower cooling coefficient than C. Its higher rate of drop
can be attributed to its higher initial temperature. Although the initial
asparagus and air temperatures were similar in A and K, the latter car
(loaded 8 wide) showed a slightly higher cooling coefficient and a greater
rate of temperature drop. The 7-wide "B" end of car N cooled somewhat
more slowly than the 8-wide "A" end.

Importance of Air Volume. — The two best records with portable-fan
precoolers were obtained in car M and the "B" end of car L (table 1).
Though the high rates of drop in these were partly due to low air tem-
peratures, the cooling coefficients are also high. The coefficient of the "A"
end of car L is surpassed only by car K, car C not being comparable be-
cause of a different number of rows of crates. These results show the
importance of proper air volume, which was only 2,450 to 2,750 cubic
feet per minute in each end of cars D to K, and 2,900 to 3,200 cubic feet
per minute in L and M. The average of the coefficients of cars L and M
was 0.14, as compared with 0.10 for D, F, H, and K. These results indi-
cate that with the greater air volume equivalent cooling was obtained in
about 70 per cent of the time. The greater circulation rate not only
effects better transfer of heat from asparagus to air, but also results in
a lower return air temperature, which assists in cooling the more remote
parts of the load.

In general for forced convection across irregular surfaces, the heat-
transfer coefficient increases with the 0.6 to 0.7 power of the velocity. 10
Air friction in turbulent motion increases with the 1.6 to 2.0 power,

15 McAdams, W. H. Heat transmission, p. 227-233. McGraw-Hill Book Co., New
York. 1933.

BUL. 600 J PRECOOLING AND SHIPPING ASPARAGUS 21

while fan horsepower increases with the 2.6 to 3.0 power of the velocity.
Thus a 20 per cent increase in air-circulation rate will presumably in-
crease heat transfer 14 per cent but will incur a 40 per cent rise in re-
sistance to air flow because of friction and require 70 per cent more
power. Clearly, there is some limit beyond which increasing air volume
is not justified. One must also remember that propeller type fans of
simple designs do not usually perform well at static pressures greater
than V2 inch of water. For example, the air volume with two 20-inch,
4-blade, 1,740 r.p.m. fans at each end of the car would be only 35 per
cent greater than with one, because of the decreased volume per fan at
the higher resistance occasioned by the greater air flow.

Importance of Air Distribution. — The importance of proper distribu-
tion is seen by comparing car N with car F (table 1) . The fans in car N
were rated at 14,000 cubic feet per minute total and probably delivered
10,000 cubic feet per minute against the resistance of the radiator section
and load, while in F the fan capacity did not exceed 5,500 cubic feet per
minute. (Jar F showed about the same cooling coefficient and about the
same drop per hour. Raising the fan horsepower without securing effec-
tive distribution does little good, for the fan-motor energy appears as
heat and tends to offset cooling of the air. The 3 kilowatts used in car N
will warm 10,000 cubic feet per minute approximately 1° F, which is 12
to 15 per cent of the total air-temperature rise.

Value of Low Air Temperatures in Rapid Cooling.- — A comparison of
cars H and D discloses the effect of low air temperature. Although the
cooling coefficient was similar in car H, the drop per hour was greater
because of the lower air temperature. The low air temperature was ob-
tained by applying to the ice 500 pounds of salt, as compared with a
total of 250 pounds in car D. Except when the load is initially cool,
close attention is necessary to secure the cold-air temperature desired.
With asparagus loads starting at 70° to 75° F, one can obtain satisfac-
tory air-blast temperatures by adding 250 to 400 pounds of salt when
the ice is barred down before the fans are turned on. As a rule additional
salt must be supplied when the bunkers are re-iced 3 to 5 hours later, in
order to maintain satisfactory blast temperatures. In case the air-blast
temperature again rises, but the bunkers contain enough ice to supply
the refrigeration needed, the ice is again barred down to close up the
large air channels which have resulted from meltage. Where loads are
initially cool (60° to 65°), cooling to a satisfactory temperature may be
obtained without re-icing during precooling and with the use of only a
little salt. This can be seen by comparing cars D, C, F, and H with A, B,
K, L, and M. As operated, the brine-cooled unit did not produce low
enough temperatures during the first part of the precooling period to

University of California — Experiment Station

lower the respiration rate quickly. This fact can be seen by comparing
carN (fig. 9) with car M (fig. 8).

The time required at a uniform cooling coefficient to lower the tem-
perature of the load to 40° F is reduced by 30 per cent if a blast tempera-
ture of 31° F instead of 36° is used, while another 10 per cent reduction
in time required is obtained if the air temperature is dropped to 29°.
Since the average freezing temperature of asparagus as given by Rose,
Wright, and Whiteman, 16 is 29.8°, air temperature should not be main-
tained below 30° for very long periods.

TABLE 2

Deviation of Temperature Taken at Top-Center Doorway Crate
from Average Temperature of Asparagus in the Car

Elapsed time

Car A

Car B

Car C

Car D

Car F

Car H

Car K

Car L

CarM

hours
1

+0.6

-5.0
-1.5

-3.0
-3.7
-3.2
-3.1

-2.9
-2.7
-2.6

+2.5
+2.1
+1.6
+14
+0.9
+0.7
+0.5

o p

+1.1

+ 1.7
+2.1
+2.2
+2.0
+1.8
+ 15

o p

+3.9
+3.3
+2.6
+18
+1.6
+16

o p

+10
-10
+2.1

-2.4
-2.1
-18

op
-3.9
-5.5
-5 2
-5 2
-5.8
-4.1
-3 3

o p
-18

-4 1

-1
-1

-1
-1
-1

4
5
2
1

-7.1

-7 6

-7 2

-5.8

-4.0

A high initial asparagus temperature results in a rapid cooling rate
if enough ice and salt are provided to keep air temperatures low, as
shown by a comparison of cars K and F. In car K, with initial tempera-
ture of 72.7°, the drop per hour was 2.4°, while in car F, with initial
temperature of 56.5°, the drop per hour was 1.5°. Although the air tem-
perature in both was about the same, car K required more salt and ice
because it was warmer. One must recognize this fact when analyzing data
giving only the rate of temperature drop. With the same air tempera-
tures and cooling coefficient, a 75° F load requires from 25 to 35 per cent
longer to cool to 40° F than a 60° F load and also requires from 65 to 75
per cent more refrigeration.

Temperatures of Various Positions in the Load and Average Tempera-
ture of Load. — As mentioned above, a common practice in precooling is
to take commodity temperatures at the easily accessible top-doorway
position. Table 2 shows the differences between temperatures at this
position and the average temperature of asparagus obtained from nine
positions distributed as indicated in figure 6. The top-doorway position
was 1.0° F to 7.6° F cooler, in most cases, than the average asparagus
temperature of the load. The exceptions were in cars C, D, and F, where
the doorway position was higher than the rest of the load. In these cars

16 Rose, Dean H., R. S. Wright, and T. M. Whiteman. The commercial storage of
fruits, vegetables, and florists' stocks. U. S. Dept. Agr. Cir. 278:20. 1933.

Bul. 600J

Precooling and Shipping Asparagus

the average asparagus temperature was low, and the air temperature
was not so low as in the other cars.

Apparently, therefore, the cooling of the load cannot well be judged

TABLE 3

Temperature and Position of the 3 Warmest Crates in Each Car* at the

End of the Cooling Period

Warmest

Second warmest

Third warmest

Car

Location

Temper-
ature,
degrees F

Location

Temper-
ature,
degrees F

Location

Temper-

Layer t

Row}

Stack!

Layer f

RowJ

Stack!

Layer f

RowJ

Stack!

ature,
degrees F

55.5

49 2

49.0

48.7

46 2

42.8

47.0

44 5

43.8

42.7

41.8

44.6

44 5

42 3

48 1

48.0

47 6

44.1

42.4

40.5

45.6

43.3

42.7

* Cars are usually 4 layers high, 7 or 8 rows wide, and 9 or 10 stacks long in each end.

t Numbered from bottom to top.

t Numbered from loading door of car.

! Numbered from bunker.

TABLE 4

Temperature and Position of the 3 Coolest Crates in Each Car* at the

End of the Cooling Period

Coolest

Second coolest

Third coolest

Car

Location

Temper-
ature,
degrees F

Location

Temper-
ature,
degrees F

Location

Temper-
ature,

Layer f

RowJ

Stack!

Layer f

Row*

Stack!

Layerf

Row*

Stack!

degrees F

43 5

46.0

51.5

37.8

39.0

40.4

39.7

39.9

40.1

41.0

41.4

36.5

37.0

39.4

37.2

38.6

37.2

38 1

38.3

34.5

35.4

36 4

35 4

35.5

* Cars usually 4 layers high, 7 or 8 rows wide, and 9 or 10 stacks long in each end.

t Numbered from bottom to top.

t Numbered from loading door of car.

! Numbered from bunker.

by the temperature in a top-doorway crate, for in one case the average
temperature recorded here was 7.6° F lower than the average of the car.
The temperature in the top crate at the bunker is a much more reliable
index of the average load temperature in cars of asparagus cooled, like

24 University of California — Experiment Station

those tested, by inside fans. Temperatures of several crates should be
taken if possible, to reduce the error from the selection of a crate that
was much warmer or cooler initially than the average of the car.

The warmest positions at the end of the precooling period are shown
for nine cars in table 3. In five of the nine cars the warmest positions
were in the bottom layer, the center rows, and the quarter-length stacks.
Of the 27 positions obtained from the 3 warmest positions in each of the
nine cars, 12 were in the quarter-length stacks, 9 in the bunker stacks,
and 6 in the doorway stacks. Of the 12 warmest quarter-length positions,
7 were in the bottom layer, 2 in the top layer, and 3 in the middle layer.
Usually the warmest positions were in the two bottom layers, 16 of the
27 high temperatures being recorded in these layers.

As a rule the coolest temperatures at the end of the precooling period
were in the top and next to the top layers, 18 of the 27 lowest tempera-
tures falling in this category (table 4). As many cool quarter-length as
doorway positions were found.

Cooling the top of the load is quite desirable. Although the bottom
of the load is well taken care of en route bv natural air circulation in the
car, the top would tend to remain warm unless its temperature had been
brought down to the desired carrying temperature. When fans are shut
off, respiration and heat from the bottom tend to warm the top layers
even though the average load temperature rises but slightly. This fact
explains the increase in temperature of top layers after precooling, as
noted in shipping tests made in these investigations.

SHIPPING TESTS

In these investigations shipping tests were made in most of the cars for
which precooling records were obtained. When the variety, method of
packing, or type of asparagus was to be tested for its effect on carrying
quality, test crates of the asparagus of different varieties and samples
of the several packs were placed in similar positions in the same car so
that no difference in loading or transit conditions would be encountered.
They were then inspected on arrival at destination, and any differences
noted. Similarly, when the method of refrigeration or loading was to be
tested, identical crates were placed in comparable positions in pairs of
cars that were loaded differently or shipped under different refrigera-
tion tariffs. In each car containing test crates, Ryan thermometers were
placed in several crates, a bunch of asparagus being removed and the
thermometer tied in the crate in its place. Thus, for each test shipment,
temperature records were available from the time of loading through
precooling and transit until the unloading ; and the carrying quality was

Bul. 600]

Precooling and Shipping Asparagus

ascertained by careful inspection of the test crates. As the cars were
usually shipped in pairs in order that one method of shipping or hand-
ling might be compared with another, the results are presented under
headings giving the object of the particular test. A comparative shipping
test between nonprecooled and precooled carloads was planned, but the
refusal of interested shippers to risk a carload of asparagus without pre-

TABLE 5

Transit Temperatures (12 Noon) in Precooled Asparagus Cars Shipped by
Standard and Modified Refrigeration*

Car Af (rule 247) ; modified refrigeration

Car BJ; standard refrigeration

Days after
shipment

Top-
doorway
crate

Bottom
quarter
length

Top
quarter
length

Top

doorway

crate

Bottom
quarter
length

Top
quarter
length

op
41
44
43
42
41
40
41
41
40
40

o p

43
40
40
40
39
38
38
39
39
38

° p
43

48
48
47
45
45
45
45
45
44

°F
35
45
43
43
42
43
42
42
40

op
38
38
38
38
38
38
38
38
37
37

° p
40

* Car A shipped from Thornton, California, to New York, April 13 to 23, 1933; Car B, April 14 to 24,
1933.

t Average outside temperature 54° F. Outside temperatures were obtained from the Weather Bureau
stations in towns through which the cars were routed and are mean temperatures.

t Average outside temperature 56° F.

cooling made such a test impossible. The practice of precooling became
general in 1933.

Standard versus Modified Refrigeration. — Cars A and B in the test
were loaded at the same shed with crates 7 rows wide, car A being loaded
on April 12, 1933, and car B on the following day. Each car was shipped
the morning after loading to New York City via the Western Pacific,
Denver & Rio Grande Western, Missouri Pacific, Wabash, and Erie rail-
roads. These two cars were precooled in the same way, the asparagus at
the end of precooling showing an average temperature of 49.0° F in
car A and of 44.0° F in car B.

Car A was shipped under rule 247, a modified method of refrigeration
under which the shipper or carrier pre-ices the car and the carrier re-ices
the bunkers once in transit at a regular icing station designated by the
shipper. Car B was shipped under standard refrigeration, under which
the carrier pre-ices the car and replenishes the bunkers to capacity at
all regular icing stations.

26 University of California — Experiment Station

The transit temperatures (table 5) were about the same in the car
shipped by standard refrigeration as in the car shipped with only one
re-icing (rule 247). In transit the temperature in the top-doorway
crates in both cars rose to 44°-45° F, then gradually declined to 40° F
in 6 days in car A and in 9 days in car B. At the bottom quarter-length
position in car A the temperature held fairly close to 38°-40° F after
the first day, and in car B to 37°-38° F throughout the entire trip. The
top quarter-length position in car A ranged between 43° and 48° F, a
few degrees warmer than the top-doorway position. In car B the Ryan
thermometer in this position failed to record after the fourth day.

The condition on arrival of the asparagus shipped in these cars was
practically the same. There was little difference that could be attributed
to transit conditions, and both lots sold for approximately the same
price. Car A (rule 247) arrived with bunkers one-fourth full of ice,
whereas car B (standard refrigeration) arrived with bunkers seven-
eighths full. The asparagus in car A was in excellent condition, show-
ing practically no slime on the cut basal ends of the spears and no mold,
with only occasional sprouting and slight shriveling, mostly above the
bottom ribbon of the bunch. In car B, slightly less wilting was noted
than in car A, although more spears showed slime on the cut ends. There
were 22 butts showing slime in three test crates in car B as compared
with 5 in the same number of crates in car A. The temperature records
and inspection records on these cars indicate that after precooling, the
asparagus carried as well with one re-icing in transit as it did with 12
re-icings, under the outside temperature conditions encountered on
the test.

Loading 7 Rows Wide, 4 and 5 Layers High versus 8 Rows Wide, 4
Layers High. — Two different methods of loading were in commercial
use : one in which the asparagus crates were loaded 7 rows wide, 4 layers
high in one end, 5 layers high in the other, allowing about 2 inches of air
space between the crates ; and another in which the crates were loaded
8 rows wide and 4 layers high throughout with less than 1 inch between
the wide part of the pyramid-shaped crates. Both methods of loading
permitted about the same number of crates per car, with 10 stacks in
one end and 9 stacks in the other.

To compare these methods of loading, two cars were loaded at the same
shed the same day with similar asparagus and were precooled with the
same type of equipment for 13 hours. The average asparagus tempera-
ture in car C, loaded 7 rows wide, was 42.1° F at the end of the precool-
ing period ; in car D, loaded 8 rows wide, 43.0° F. The latter car, being
a little over 3° warmer when loaded, was actually cooled more than car C
(table 1).

Bul. 600]

Precooling and Shipping Asparagus

The asparagus in the top-doorway position in the car loaded 7 rows
wide was 4°-5° cooler throughout the transit period than that in the same
position in the car loaded 8 rows wide (table 6). At the bottom quarter-
length position it was 2°-3° cooler, but this small difference was prob-
ably not significant.

TABLE 6

Transit Temperatures (12 Noon) in Precooked Asparagus Cars,
Loaded 7 and 8 Eows Wide*

Car Cf; loaded 7 wide

Car Df; loaded 8 wide

Days after shipment

Top-
doorway
crate

Top
quarter
length

Bottom
quarter
length

Top-
doorway
crate

Bottom
quarter
length

° p
36
42
41
41
38
38
38
38
38
38

o p

36
43
44
42
41
42
42
42
40
40

° p
40
38
36
36
36
36
36
35
35
35

° F
41
46
46
45
43
43
43
42
42
42

OJjl

38
37

* Shipped by standard refrigeration from Antioch, California, to New York, April 16 to 25, 1933.
t Average outside temperature 46° F.

TABLE 7
Inspection Report of Test Crates in Cars Loaded 7 and 8 Rows Wide

Position of crate in the car

Temperature

range
in degrees F

Number of

bunches
considered

Per cent of spears

showing slime

on butts*

Car C; loaded 7 wide

Top doorway

Top quarter length ....
Bottom quarter length .

42 to 36
44 to 36
40 to 35

3 5

6.4
5

Car D ; loaded 8 wide

Top doorway

Top quarter length.
Bottom quarter length .

46 to 41

43 to 37

5
4.6
4.0

* The slime, an early stage of bacterial soft rot, reported in this and other inspections was not serious,
involving only the cut ends of the spears, which are usually discarded when the asparagus is cooked.

Inspection on arrival revealed no significant differences in the aspara-
gus shipped in these cars (table 7). The spears were in excellent condi-
tion except for the few that showed butts infected with slime, probably
bacterial soft rot. Mold on the tips of the spears, which had caused loss
the previous season, was not encountered in these cars.

University of California — Experiment Station

Carrying Quality of Different Varieties; Loose Pack, Unwrapped
Bunches, and Wrapped Bunches; and Asparagus Grown on Peat Soil
and Sediment Soil. — In car E, shipped from Thornton, California, on
April 19, 1933, to Philadelphia, by rule 247, crates of asparagus of differ-
ent varieties and packs, grown on different soil, were loaded to ascertain
whether some of the beliefs concerning carrying quality were founded

TABLE 8

Preoooling and Transit Temperatures in Variously

Packed Crates of Asparagus*

(Car E)

Elapsed time

Top quarter-length position

Wrapped

Unwrapped

Loose

Top-doorway position

Wrapped

Unwrapped

Loose

Precooling temperatures

Hours

Start.

Temperature drop .

o p

62 7

63 3

63 2

60 4

52 2

52 6

57 5

56 1

45 5

44 1

44 3

50 7

51 3

40 9

39 4

40 3

45.7

21.8

23.9

22 9

19 3

13 4

60 8
50.1
43 3
38 6
22 2

Transit temperatures!

Days

2.
3.
4.
5.

6.
7.
8.
9.
10.

° F

o p

op o

* Shipped by modified refrigeration (rule 247) from Thornton, California, to Philadelphia, Pa., April
18 to 28, 1933.

t Average outside temperature 47° F.

on fact. This car was loaded 7 rows wide and precooled in the usual way,
the average asparagus temperature reaching 42.5° F at the end of pre-
cooling.

The test crates were all loaded in the fifth and doorway stacks, in the
top layer, and in the center rows of the car, where they would be exposed
to similar air conditions. Both the unwrapped and the wrapped were
bunched, usually 12 bunches per crate, the wrapped being enclosed in
about a 4-inch band of parchment paper. The loose pack was not bunched
nor wrapped. In the variety test, bunch-packed Mary Washington,
Argenteuil, and Conover's Colossal were used. Crates of Mary Washing-
ton asparagus grown on peat and sediment soil were also included in
the test.

Bul. 600J

Precooling and Shipping Asparagus

The results in table 8 do not indicate any significant differences in the
cooling rate of the different packs. The position of the asparagus crate
with respect to air currents is of more importance, no doubt, than the
method of packing, for the unwrapped bunch pack in stack 5 showed the
most cooling, while in the doorway stack this pack showed the least cool-

TABLE 9

Condition of Asparagus on Arrival in Philadelphia as Affected by Types

of Soil, Variety, and Method of Packing

(Car E)

Position of

Pack

Soil

Spears showing

crate

Variety

Mold

Slime

Remarks

Top doorway

Mary Washington
Mary Washington
Mary Washington
Mary Washington
^ Argenteuil

Wrapped

Unwrapped

Loose

Wrapped

Peat

Sediment

Peat

per cent*
1.8
6
0.0
0.0
0.2

per cent*

2
1.8

0.6

(Considerable
\ bruising on sides
[of spears

Top quarter
length

Mary Washington

Mary Washington
Mary Washington
Mary Washington
Argenteuil
^Conover's Colossal

Wrapped

Unwrapped

Loose

Wrapped

Peat

Sediment

Peat

2.0

6
14
2
2.0

3.6

1.6
0.0
0.0

0.4

[More bruising
\ than in other
1 wrapped bunches
[Considerable
\ bruising on sides
[of spears

* The percentages were obtained from the number of spears counted which were moldy or slimy, with
40 spears per bunch estimated and 12 bunches per crate inspected — except crates with Ryan thermometers,
11 bunches being packed in these crates.

ing. The temperatures were taken with the bulbs of the resistance ther-
mometers placed as near the centers of the crates as possible.

Temperature records taken in transit on wrapped, unwrapped, and
loose-pack crates of Mary Washington (table 8) show that at the top-
doorway position the unwrapped asparagus was consistently cooler than
the wrapped throughout the trip. At the top quarter-length position
there was little difference.

The inspection of the crates of different packs (table 9) revealed few
differences, all the asparagus arriving fresh and firm ; several spears
were affected with mold, and some spear butts with slime. The mold and
slime found in the inspections were confined to small areas and had little
commercial importance, only a few spears being so affected. Bruising-
was found in crates of unwrapped bunch pack ; apparently, therefore,
the parchment wrap somewhat protects the tender spears, as well as
"dressing up" the pack. There was no difference in the carrying quality
of the different varieties or of the asparagus grown on different types
of soils.

University of California — Experiment Station

Ice-Water Dipping versus Portable-Fan Precooling. — Cars F, G, H,
and J were shipped to compare the transit temperatures and the condition
upon arrival of asparagus cooled by portable fans and asparagus cooled
by standing in ice water before packing, with a short period of precool-

TABLE 10

Transit Temperatures (12 Noon) in Cars Loaded with Asparagus Cooled
by Ice-Water Dipping and Fan Precooling — First Test*

Top quarter-length position

Bottom quarter-length position

Days after shipment

Car Gt;

ice water and

fan cooled

Car Ft;

fan
cooled

Car Gt;

ice water and

fan cooled

Car Ft;

fan
cooled

o p

32
41
44
44
44
44
43
43
42
42

37
35
35
35
35
35
35
35
35
35

op
36

* Shipped under standard refrigeration from Antioch, California, to New York, April 20 to 29, 1933.
t Average outside temperature 52° F.

TABLE 11

Condition of Asparagus Cooled by Ice-Water Dipping and Fan
Precooling on Arrival at New York

Car
No.

Method of
cooling

Spears showing mold

Spears showing slime

Test
No.

Top
doorway

Top
quarter
length

Bottom
quarter
length

Top

doorway

Top
quarter
length

Bottom
quarter
length

/ G*
[ F*

/Jt
\H t

Ice water and fan . . .
Fan

per cent
0.0

0.0
2 3

per cent
0.0

0.4
0.0

per cent
0.0

per cent
2.7
0.7

2.0
3.4

per cent
1.6
0.7

1.8
3 2

per cent
0.0
0.9

Ice water and fan ....
Fan

* Shipped under standard refrigeration from Antioch California to New York, April 20 to 29, 1933.
Average outside temperature en route 52° F.

t Shipped under standard refrigeration from Antioch, California to New York, April 28 to May 9, 1933.
Average outside temperature en route 54° F.

ing in the car. The asparagus in car F, precooled in the usual way, aver-
aged 40.5° F after 11 hours of fan precooling; that in car G, precooled
first with ice water and then by car precooling, reached 40.1° F in 6
hours, 38.8° F in 8 hours. The temperatures in transit (table 10) in
these two cars shipped under standard refrigeration were about the
same except at the top quarter-length position on the eighth and ninth

Bul. 600 J

Precooling and Shipping Asparagus

days, when the fan-cooled car was 4°-5° cooler than the car cooled with
ice water and fans. The asparagus in both cars arrived in excellent con-
dition, no differences between the two cars being discernible.

As indicated in the inspection (table 11), no significant amount of
mold was found ; and the slime recorded affected only the cut base of the
spear and had little commercial importance. Three crates completely
submerged in ice water and loaded at the top-doorway position likewise

TABLE 12

Transit Temperatures (12 Noon) in Cars Loaded with Asparagus Cooled
by Ice-Water Dipping and Fan Precooling — Second Test*

Days after
shipment

Top-doorway position

Days after
shipment

Top-doorway position

Car Jf;

ice water and

fan cooled

Car Hf;

fan
cooled

Car Jt;

ice water and

fan cooled

Car Hf;

fan
cooled

° p

40
41
41
42
42

38
43
43
42
42
42

9.
10.
11.

42
42
42
42
42

* Shipped under standard refrigeration from Antioch, California, to New York, April 28 to May 9, 1933.
t Average outside temperature 54° F.

arrived in good condition, aside from a few slimy butts. Neither water
cooling nor complete submersion had any deleterious effect on the aspara-
gus, nor did they result in its remaining fresher than when precooled in
the usual way.

In the second test of cooling the asparagus with ice water, that cooled
by this method averaged 39.1° F after 5 hours of fan cooling; and the
asparagus in the car cooled by fans alone, averaged 40.8° F at the end
of 11% hours. These cars were shipped under standard refrigeration to
New York City. Temperatures in transit (table 12) were again practi-
cally identical in the two cars.

As shown by the inspection report on test crates placed in the two
cars (table 11) , there was very little mold or slime. The few defects noted
had no commercial significance. The slime on the cut base of the spears
usually dried when they were removed from the crate. No difference in
freshness was evident between these two pairs of boxes, either at the
time of unloading or 2 days later after the asparagus had been held in
storage at 50° to 60° F. It was true, however, that the asparagus in these
two cars, shipped late in the 1933 season, was a little more wilted than
the asparagus inspected in the seven other cars previously shipped.

Cellophane Wraps and Caps for the Bunches. — In car F, a companion

32 University of California — Experiment Station

for the water-cooled car G, a shipping test was made in which the aspara-
gus bunches were wrapped with cellophane of two types, non-moisture-
proof and moistureproof . On arrival in New York those wrapped with
the non-moistureproof grade were about like the bunches wrapped in the
usual way, and the inner surface of the cellophane wrap was dry. In the
case of the other grade, moistureproof, considerable moisture collected
on the inside of the cellophane wrap and on the stalks. This condensed
moisture appeared to make the asparagus somewhat fresher. No mold
was present in either case.

Cellophane was again tried in 1934, four crates being shipped in car M.
The bunches in these crates were covered with cellophane bags, non-
moistureproof and moistureproof grades being used. These bags were
placed over the tops of the bunches and extended to the base. When
unloaded, condensed moisture was found on the inside surfaces of bags
of both grades, with more on those of moistureproof cellophane. When
held at room temperature, about 70° F, for 2% days, both lots showed
some mold development. That covered with moistureproof cellophane
was more moldy, 68 spots being found in 6 bunches against 17 spots in
the same number of bunches wrapped in the other grade. The presence
of mold and the condensation of moisture made this lot less attractive,
and the cellophane bags were not favorably received by the trade. The
asparagus in these crates, however, was very fresh and, with the ex-
ception of the small mold spots indicated, was in excellent condition.

Carrying Quality of Long-Green and White-Butt Asparagus as Af-
fected by Delay in Removal from the Field after Cutting. — That poor
condition on arrival may be caused by allowing the asparagus to remain
in the field on warm days after cutting was an opinion advanced by some
agencies interested in asparagus shipping. It was likewise claimed that
in warm weather spears elongate faster, so that by the time they are
cut many spears are green the full length rather than about two-thirds
the length and are harder to cool and carry to market in good condition.
Respiration tests conducted during the previous season had indicated
that this "long-green" asparagus is more active physiologically than
spears which are about two-thirds green. Conceivably, therefore, a car-
load of asparagus, warm when loaded, might evolve so much heat from
respiration that precooling would be difficult, transit temperatures high,
and mold growth widespread on arrival.

On April 9, accordingly, a day when when air temperature in the
shade reached 85° F, "long-green" and "white-butt" asparagus was cut
from the University of California plots on Ryer Island. A portion of
each type was brought in from the field shortly after it was cut, and
duplicate lots were allowed to lie on the ridges for 5 hours during the

Bul. 600

Precooling and Shipping Asparagus

middle of the day. All the asparagus was held in the packing-house over-
night and packed the next day.

Field temperatures taken with thermocouples inserted in the spears
(fig. 11) showed the standing spears to be from 15° to 25° F above air
temperatures. Those which were at the bottom of the small piles (10 to
20 spears) left by the cutters were little if any warmer than the air. In

/ao

Fig. 11. — Field temperatures of asparagus.

the morning those on the east side of the piles warmed rapidly, reaching
30° F above air temperature, but dropped as they became shaded in the
afternoon, whereas those on the top of the piles continued to warm after
noon. Apparently spears which were cut early and left on the ridges
averaged no warmer when they were picked up than those cut later and
picked up at once, since part of the piles were shaded. This, of course,
depended on the sun, which was bright, and the wind, which fluctuated
from 1 to 2 miles an hour. At 2 :30 p.m., while the asparagus was still at
the field shed, spear temperatures of 74° to 82° F were noted; at
5 :40 p.m., after the asparagus had been hauled to the packing shed in
field lugs, the temperature had risen from 80° to 89° F. During the night
the packing-shed temperature fell to 47°, which probably lowered and
equalized the temperatures of the asparagus in the different lots, as
indicated by the uniform temperatures when loaded.

University of California — Experiment Station

The asparagus was packed and loaded in groups of packages in the
top and next-to-top layers in the car at quarter-length positions, all the
long-green being loaded in one group and the white-butt in the other.
The groups consisted of 4 to 8 crates of each type of asparagus. The

TABLE 13

Precooling and Transit Temperatures of Long-Green and White-Butt

Asparagus Handled Promptly and Alix)Wed to Lie in

Field for 5 Hours — First Test*

(Car K)

Long-green

White-butt

Top layer
in car

Next to top
layer in car

Top layer
in car

Next to top
layer in car

Elapsed time

ridges
5 hours

Collected

im-
mediately

ridges
5 hours

Collected

im-
mediately

ridges
5 hours

Collected

im-
mediate! j'

Collected

im-
mediately

Precooling temperatures

hours

OJ?

Start

74.3

72 5

72.7

71.7

73 2

72.7

68.8

60 5

64 6

68.9

60 7

66 4

70 3

58.1

49.5

53 7

48.9

53.1

61.5

49 1

43 8

43
40 2

45 9
42 5

52.8
48

42 1
39

44
39 5

47.6

Total drop in

temperature

30 5

32 3

30 2

23.7

33.7

25.1

Transit temperatures!

days

°F

. . .

46
45

43
43

41
40

45
44

* Shipped under modified refrigeration (rule 247) from Antioch, California, to New York, April 10 to
19, 1934. Crates loaded at quarter-length positions.

t Average outside temperature 57° F.

rest of the load was the usual type of shipping asparagus, 2 to 3 inches
of white on each spear. The precooling records (table 13) indicate that
there was no significant difference in the temperature of the asparagus
by the time it was loaded, irrespective of field treatment or type of
asparagus. Although differences in cooling rates were observed, they
were more affected by position in the car than by type of asparagus or
temperature when loaded.

Bul. 600]

Precooling and Shipping Asparagus

The transit temperatures (table 13) ranged from about 47° F to
50° F during the first part of the trip to 40° F to 44° F on arrival at the
end of 9 days. The temperature in one crate, long-green, delayed in the
field and loaded at top quarter-length positions, ranged several degrees
higher than that in the other test crates. Inspection on arrival revealed

TABLE 14

Precooling and Transit Temperatures of Long-Green and White-Butt

Asparagus Handled Promptly and Allowed to Lie in

Field for 5 Hours — Second Test*

(Car M)

Long-green

White-butt

Next to top
layer in car

Next to bottom
layer in car

Next to top
layer in car

Next to bottom
layer in car

Elapsed time

ridges
5 hours

Collected

im-
mediately

ridges
5 hours

Collected

im-
mediately

ridges
5 hours

Collected

im-
mediately

ridges
5 hours

Collected

im-
mediately

Precooling temperatures

hours

Start

2]4

68.6
57.4
45 2
42 4
39 2

29 4

O f

70 8
57.8
43.8
41.7
39

31 8

op
69.0
63.1
51 1
47.1
42.7

26 3

70 3

62.9
49.6
45.8
41.5

28.8

66.4
57
45 1
41 8

38.7

27.7

70 2
60
48.5
43 4
39.9

30 3

68.1
54 9
43.7
41.1
38.4

29.7

70 2
56 .8

44.8

42 3

Total drop in
temperature. . . .

39.5
30 7

Transit temperatures!

days

o p

40
45
47
47
45
43
41
41
41
40

op
40
44
45
45
44
42
42
41
40
40

38
45
45
44
42
41
40
40
38
38

35
42
42
40
40
37
37
37
36
36

o p

36
42
44
44
43
42
40
40
40
38

35
41
43
43
41
40
40
39
38
37

o p

39
42
43
42
40
40
40
39
37
37

o p

35
43

5....

* Shipped under modified refrigeration (rule 247) from Antioch, California, to New York, April 12 to
22, 1934. Crates loaded at quarter-length positions.

t Average outside temperature 53° F.

no difference of any consequence, all the asparagus arriving in excellent
commercial condition. Slightly more wilting was noticed in the long-
green, 4 out of 7 test crates of this type showing wilting, as compared
with only 1 in 5 of the test crates of white-butt. The extent of wilting
was not great enough to be of commercial importance. The long-green
also showed more butts affected with slime and more mold spots than
the white-butt ; but again the infections were in very early stages and

36 University of California — Experiment Station

did not affect salability. No differences were noticed between asparagus
left for a time in the field and that picked up immediately.

Several days later in the season these tests were repeated, essentially
the same procedure being* followed as in the previous tests. After pack-
ing and loading, the asparagus that had been left in the field was
actually cooler than the lot handled promptly, even though it was ex-
posed to field temperatures of 85° F or more. Records indicated, how-
ever, that this type of handling resulted in a loss in weight of 4 per cent
in 2% hours under air temperatures ranging from 78° to 69° F with
relative humidities of 25-35 per cent. No significant differences in cool-
ing rates were observed (table 14).

The temperatures in transit (table 14) do not indicate that the type of
asparagus or the method of handling had any effect on carrying tem-
perature after precooling. Inspection of the test crates when unloaded
revealed no significant differences in appearance or freshness between
long-green or white-butt, or between lots picked up in the field imme-
diately or those allowed to lie in the sun for several hours. Again detailed
inspection showed more long-green spears affected at the cut end with
early stages of slime than white-butt spears. The affected areas were so
small as to be of no consequence commercially. Both lots were practically
free from mold. Spears of asparagus of small diameter were usually
more wilted than larger ones.

In a test made in this car, asparagus immersed in ice water and aspara-
gus packed in the usual way with only the base of the stalks wet, carried,
as in previous tests, equally well — further evidence that wetting did no
damage under transit conditions encountered in these tests.

DISCUSSION AND SUMMARY OF SHIPPING TESTS

The shipping tests made in 11 cars of asparagus during 1933 and 1934
are summarized in table 15. The asparagus carried well in all the tests,
and in no case was excessive mold growth encountered. The transit tem-
perature in crates loaded in the top layer, doorway stack, as recorded
by the Ryan thermometer, averaged from 39° to 44° F in all the cars
except car K. In this car, average temperatures of 48° and 46.3° F were
obtained in crates of long-green asparagus, and 46° and 43.7° F in
crates of white-butt asparagus. Spots on the tops of spears (early stages
of mold growth) were found in greater numbers on the long-green than
on the white-butt. Though the amount of mold was not commercially
significant, its greater prevalence on this type of asparagus in car M as
well as car K was evidence that the succulent long-green, of high respira-
tory activity, heat-evolving capacity, and perishability, offered greater
transit problems than the more fibrous white-butt type.

Bul. 600]

Precooling and Shipping Asparagus

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On ridge 5 hours
Collected immed'ly

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On ridge 5 hours
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38 University of California — Experiment Station

The lowest average transit temperature for the trip at the top-door-
way position was 38.8° F, recorded in car C. This car was shipped under
standard refrigeration in April, 1933, when the mean outside tempera-
ture for the trip was 46° F. Car K, in which the highest temperatures
were recorded, was shipped with one re-icing in transit in April, 1934,
when the mean outside temperature was 57° F for the trip.

Under the conditions of these tests precooled asparagus carried as well
with only one re-icing in transit as with 10 or 12 re-icings

There was no apparent difference in the condition on arrival of aspara-
gus shipped in the 7-wide, 5-high load and 8-wide, 4-high load.

The type of soil on which grown and the variety or method of packing
(loose in crates, bunched and wrapped, or bunched and unwrapped) had
no bearing on carrying quality, although less bruising was observed on
wrapped than on unwrapped bunches.

Asparagus wet by submerging two-thirds of the length of the spears
in ice water 10-12 minutes carried as well as asparagus not subjected to
this treatment but precooled with fans. Since asparagus completely sub-
merged in water arrived on the market in good condition, practically
free from mold and rots, the belief that wetting asparagus is harmful
appears to be erroneous. Cooling with ice water therefore appears to be
a safe practice.

Cellophane wraps or caps for the bunches were of no advantage. Con-
siderable moisture collected on the inside surface of the moistureproof
grade and on the spears of asparagus, and slightly more mold developed
on this lot than on the lot wrapped with parchment paper or the lot with
the non-moistureproof cellophane cap.

Delay in picking up the asparagus from the field was not a factor in
carrying quality in these tests. Asparagus handled in this way was no
warmer than that cut later and picked up about as soon as cut. The tem-
perature of the asparagus was affected not by the length of time in the
field but by exposure to the sun and by air circulation. Spears standing
in the field in direct sunlight were warmer than cut spears in the bottom
of the pile, shaded from the sun. Although leaving the asparagus in the
field for several hours is not a good practice, these limited tests indicate
that it would not account for heating in the refrigerator car, high transit
temperatures, and excessive mold growth. Quality is lost by any delay in
getting the asparagus under refrigeration, as indicated by the work of
Bisson, Jones, and Bobbins. 17 The moisture lost in delayed handling
from the field would also result in decreased tonnage.

17 Bisson, C. S., H. A. Jones, and W. W. Robbins. Factors influencing the quality
of fresh asparagus after it is harvested. California Agr. Exp. Sta. Bui. 410:1-27.
1926. (Out of print.)

Bul. 600 J

Precooling and Shipping Asparagus

The present practice of precooling asparagus before shipment to an
average temperature of about 40° F throughout the car insures transit
temperatures low enough to prevent mold growth, as indicated by these
shipping tests and by the inspection of commercial shipments that have
been thoroughly precooled. After thoroughly precooling, shipping with
one re-icing in transit has been satisfactory throughout most of the
season.

TABLE 16
Respiration Rates of Asparagus, 1933 Season

Long-green

White-butt

Temperature,
degrees F

Hours after cutting

Milligrams of carbon dioxide
per kilo hour

6 to 7

7 to 12

564 4
472.4
214 5
196 6

576.2
430

50 to 55

, 123 to 129

159.7
136 7

' 7 to 12

50 to 72

123 to 149

214 1
84.4
74
74.9

186.9
64.0
58.1

, 200 to 240

63.8

' 7 to 25

50 to 95 •

63.4
49.1
40 2
36 4

75.2
43 5

123 to 170

34.1

, 200 to 240 .

37.0

7 to 25

56 8
38.3
39.2
43

39.7

50 to 95

29.6

123 to 170

31.5

^ 200 to 240

34.5

RESPIRATION OF ASPARAGUS

In the precooling and shipping experiments made with asparagus it was
necessary to know the respiration rate at various temperatures in order
to estimate the refrigeration required to precool and transport the com-
modity. No such information being available except that presented by
Benoy 18 for 30° C (86° F), studies were begun in 1933 on the respiration
of asparagus at temperatures approximating those encountered in re-
frigerator cars and storage rooms.

Respiration Studies, 1933 Season. 19 — According to reports, the aspara-
gus which had not carried well in previous seasons was the long-green
type grown under warm weather conditions. Most asparagus that is

18 Benoy, Marjorie P. The refrigeration factor in the deterioration of fresh
vegetables at room temperature. Jour. Agr. Research 39:75-80. 1929.

19 These tests were made at the Fresno laboratory of the United States Department
of Agriculture Bureau of Plant Industry.

University of California — Experiment Station

shipped has 2 or 3 inches of white on the base of the spears. The long-
green differs from this in being allowed to grow farther out of the ground
and in becoming entirely green. Since this type of asparagus looks to
be less fibrous and tough, consisting of more elongated tender shoots,
it might, conceivably, be more active and respire more rapidly, and

TABLE 17

The Effect of Holding Temperature on Heat of Respiratation of Asparagus,

Expressed as Ice-Meltage Requirement for 10 Tons of Asparagus for

24-Hour Periods, 1, 3, 6, and 9 Days after Cutting and the

Estimated Requirement for 10-Day Period*

o -p

50 c

40 c

32 c

Days elapsed

Long-
green

White-
butt

Long-
green

White-
butt

Long-
green

White -
butt

Long-
green

White-
butt

pounds

7,919

3,277

3,004

pounds

7,686

2,440

2,088

pounds
3,271
1,290
1,130
1,144

17,087

pounds

2,855

978

887

974

14,237

pounds

1,274

750

614

556

7,905

pounds

1,146

665

521

566

7,250

pounds
868
585
599
657

6,772

pounds
607
456

481

527

Total for 10 days*

5,178

* Determined from respiration rates for the 1933 season.

t Decomposition started.

t Average of requirement for 1,3,6, and 9 days multiplied by 10.

TABLE 18

Respiration Rates of Asparagus Held at 70° F, after Removal from
Storage Temperatures of 50°, 40°, and 32° F, 1933 Season

Rate during sixth to eleventh hour
of holding period at 70° F

Rate during forty-eighth to fifty-
fourth hour of holding period at 70° F

storage temperature,

degrees F

Long-green

White-butt

Long-green

White-butt

Milligrams of carbon dioxide per kilo hour

309 9
240 6
269.4

235 6
189.7
207 4

211 6
214 6

128.8

134 1

147.1

76.8

would therefore be more difficult to cool and keep cool than the usual
white-butt type. Samples of these two types, Mary Washington variety,
were cut in the Mendota district on May 29 when outside temperatures
were about 100° F. This asparagus, tied into bunches weighing about 900
grams each, was placed on moist cotton in desiccators at temperatures
of 70°, 50°, 40°, and 32° F within 2 hours after cutting. Respiration
rates of these samples were determined from time to time by passing an
air stream from the respiration chamber through potassium hydroxide
(KOH) in Truog absorption towers, the carbonate formed being titrated
with HC1 by the double titration method. An air stream of about 25
liters per hour was used, enough to change the air in the desiccators

Bul. 600J

Precooling and Shipping Asparagus

three times per hour, so that the carbon dioxide (C0 2 ) concentration
would be kept low.

The respiration rate (table 16) at 50°, a transit temperature encoun-
tered in one of the test shipments, was about two to three times that at
40° F. These data show that the respiration rate declines rapidly after
cutting- and as the temperature is lowered.

TABLE 19

Respiration Rates of Asparagus, 1934 Season

Long-green

White-butt

Temperature,
degrees F

Hours after cutting

Milligrams of carbon dioxide
per kilo hour

(

7 to 10

386.1
466.7
193.7
197.0

289.7

10 to 13

3858

51 to 56

153.2

L 125 to 141*

146.9

7 to 13

125.1
70.3
77.2
79.1

122.7

51 to 74

61.9

125 to 159

68.5

, 190 to 213

62.6

r 7to 31

85.0
47.3
48.6
37.4

72.4

51 to 117

38.5

125 to 173

35.1

190 to 237

28.7

r 7 to 31

39.8
34.0
34.9
34.2

33.3

51 to 117

30.8

125 to 173

33.0

190 to 237

29.0

* Some mold.

Table 17 gives the heat generated by 20,000 pounds of asparagus, ex-
pressed as ice-meltage requirement for various periods and tempera-
tures. (This calculation is based on the rates in table 16 and assumes that
glucose is the source of the carbon dioxide evolved in respiration and
that it gives off 673 kilogram calories of heat and 6 gram molecules of
carbon dioxide from complete oxidation of 1 gram molecule.)

The total amount of ice required to hold the load at 50°, 40°, and
32° F, exclusive of the refrigeration lost through the walls, roof, floor,
and doors of the car, is shown in the last line of figures in table 17. These
figures are obtained from the respiration rates determined 1, 3, 6, and 9
days after cutting. The table shows strikingly how much less ice is
required to offset the heat of respiration when the load is cooled to 40° F
instead of to 50° F. At 70° F more ice would be required to take care of
the heat given off the first day than would be needed for 10 days at 40° F.
At all temperatures, it is evident that the asparagus with about 2 to 3

University of California — Experiment Station

inches of the butts white respired more slowly and would give off less
heat than the long-green type. The latter consisted of spears of smaljer
average diameter than the white-butt type. Spears of each type of
asparagus of about the same diameter were selected, and a check run
was made. The long-green again respired at a higher rate.

On removal to 70° F after storage for about 10 days at temperatures
of 50°, 40°, and 32° F, the asparagus respired at the rates given in table
18. These respiration rates do not bear out the belief that asparagus held
at 32° and 40° F breaks down or "lives at a faster pace" upon removal
from storage than similar lots held at 50° F.

TABLE 20

Respiration Rates of Asparagus Held at 70° F, after Removal from
Storage Temperatures of 50°, 40°, and 32° F, 1934 Season

Hours after warming to 70° F

Long-green

White-butt

storage

temperature.

degrees F

Milligrams of carbon dioxide
per kilo hour

6 to 11

270 2
256 4
224 3

215 6

5 to 11

173

7 to 12

169.0

Respiration Studies, 1934 Season. — The respiration studies begun in
1933 were continued in 1934. The asparagus was cut for these tests be-
tween 10 and 11. a.m., April 18, near Mendota, Fresno County, Cali-
fornia. The temperature in the shade was 86° F, and the spear tempera-
tures at the time of cutting were 91°-92° F.

The long-green asparagus was cut so that the entire spear of 8 to 9
inches was green ; and the white-butt asparagus showed 2 to 4 inches of
white. About 2 hours elapsed between the time the asparagus was cut
and the time it was placed at 32° F to cool. The bunches made up of 26
spears were selected for size. In 3% hours, when the asparagus had
cooled to 40° F, the lots were divided and held at 32°, 40°, 50°, and
70° F. The determinations were begun at all temperatures the seventh
hour after cutting. The same methods of determining the respiration
rates were employed as in the previous season. The results are shown in
tables 19 and 20.

Table 19 again indicates that the long-green asparagus respires at a
higher rate than the white-butt asparagus. The respiration rates, how-
ever, were lower than those encountered in the 1933 season, when the
asparagus was harvested later under higher temperatures. Again, as-
paragus raised to 70° F after being held at 32° F did not respire so
rapidly as asparagus which had been held at 50° F or 40° F storage
temperatures before removing to 70° F.

BUL. 600] PRECOOLING AND SHIPPING ASPARAGUS 43

GENERAL SUMMARY AND CONCLUSIONS

Precooling of California asparagus before shipment to eastern markets
has become an established commercial practice because it secures a re-
duction in transit refrigeration costs and if well done, assures a satis-
factory condition on arrival.

The transit temperature of a precooled car averaged 45° F the first
day and 47° F the first 4 days, as compared with 61° F and 56° F re-
spectively for a nonprecooled car (fig. 1). Temperatures in the nonpre-
cooled car are more favorable for spoilage organisms and indicate nearly
twice as great a respiration rate, which would produce enough heat for
meltage of 2% more tons of ice. Apparently the modified refrigeration
methods under which the ice bunkers are not refilled in transit or are
filled, only once can be used for precooled cars when they would be haz-
ardous for nonprecooled cars.

The ice required to cool a carload of asparagus from 70° to 40° F in
12 hours, aside from refrigeration lost through the car, was estimated
as 6,500 pounds, the heat of respiration accounting for about one-third
of the total. In actual tests 7,000 to 7,500 pounds was melted.

The cooling equipment most commonly used is inside fans that circu-
late the air in the car through the ice bunkers, reversing the natural cir-
culation. The capacities of a recent-type, 20-inch, 2-blade, 3,450-r.p.m.
fan were 4,400 cubic feet at no static pressure and 2,900 cubic feet per
minute at 0.27 inches of water-static pressure. The static pressure in the
car ranged from 0.21 to 0.27 inches with this fan, and its operating
capacity ranged from 2,900 to 3,200 cubic feet per minute, varying with
the resistance of the ice bunker and the load in the car.

In laboratory tests marked improvement in cooling rate was obtained
by increasing air volume from 17.6 to 26.0 cubic feet per minute per stack
of 4 crates ; but no additional benefit was obtained by further increasing
the volume to 36 cubic feet per minute. A rate of 30 cubic feet per
minute per stack is equal to about 4,600 cubic feet per minute through
the loaded car.

With an air circulation rate of 3,000 cubic feet per minute at each end
of the car, the load was brought to 40° F in 70 per cent of the time re-
quired for 2,600 cubic feet per minute. Some difficulty in design of
equipment, less proportional improvement in cooling, and higher oper-
ating cost can be anticipated in attempting to secure much further in-
crease in air-circulation rates.

Air was distributed through the load more effectively with portable
fans placed at the top bunker ducts and directed downward towards the

44 University of California — Experiment Station

top center of the load than with fans placed above the brace at the door-
way and blowing directly at the ceiling.

For rapid cooling, air-blast temperatures should be maintained at
31°-32° F by using salt, re-icing to maintain bunker supplies, and
barring down bunker ice to insure thorough cooling of the recirculated
air through the bunker. Air temperatures much lower than 30° F, if
directed on the asparagus for any length of time, may freeze exposed tips.

Under present practice the average time required to cool loads from
60° to 40° F average temperature, using 2,600 cubic feet per minute of
30° F air at each end of the car, was 10 hours ; with 3,000 cubic feet per
minute, 7 hours. Loads at 75° F required 14 and 10 hours, respectively,
under similar conditions.

The average temperature of the load at the end of precooling was
from 3° to 5° F above that of the top quarter-length and doorway crates.
The temperature of the asparagus in the top layer at the bunker was
closer to the average temperature of the load under the conditions pre-
vailing in these tests.

By ice-water cooling, the asparagus temperature was reduced as much
as 22° F in 12 minutes in one test. About 10 hours' precooling with inside
fans was necessary to obtain equal reduction in temperature. No ill
effects were noticed from wetting the asparagus by this cooling method.

Transit temperatures in crates of precooled asparagus averaged from
38.8° to 48.0° F, and depended primarily on position in the car. Outside
temperatures encountered by the cars ranged from 20° to 86° F and
averaged 46° to 57° F for the trips. All cars arrived in good condition,
requiring careful, detailed inspection to disclose any differences in qual-
ity, those defects noted being seldom of commercial importance.

No significant difference was shown in precooling rate, transit tem-
peratures, or shipping quality between asparagus grown on peat and on
sediment soil, or among the Mary Washington, Argenteuil, and Con-
over's Colossal varieties.

Asparagus permitted to grow until the cut length of the spears was
all green showed a higher respiration rate than asparagus that was white
for one-third of the length at the butt end. It cooled at a lower rate,
carried a trifle warmer in transit, and showed a bit more wilting, mold,
and slime infection on arrival. The differences were hardly of commer-
cial importance. An entire car of long-green spears, however, might
reach the market in poorer condition than one of spears with white-butts,
if both were harvested during a hot afternoon, were poorly precooled,
and encountered high temperatures in transit.

In asparagus cut early but not picked up until afternoon, the initial
temperatures, cooling rates, transit temperatures, and arrival conditions

Bul. 600] Precooling and Shipping Asparagus 45

were similar to those in asparagus cut just before being picked up in the
afternoon. The field temperature was found to depend more upon the
time of picking up than upon the time of cutting. The temperature at
loading was found to depend upon the field temperature and the subse-
quent handling, which may permit dissipation of field and respiration
heat.

The method of packing, loose (not bunched) , or bunched (wrapped or
unwrapped), had no more effect on the cooling rates, transit tempera-
tures, and conditions upon arrival than the placement of the crates in
the carload. Where bunches were completely covered with moistureproof
cellophane bags, humidity within the bag was high enough to cause con-
densation on the bag, keeping the asparagus somewhat fresher but favor-
ing mold growth. Bunches wrapped with cellophane in the usual manner
were little different from those with the common parchment wrap.

The respiration rates of asparagus, even at transit and storage tem-
peratures, were found to be very high. At 32° F the rates for the seventh
to the twenty-fifth hour after cutting were 56.8 milligram of C0 2 per
kilogram hour for long-green asparagus and 39.7 milligram for spears
partially white. At high temperatures (70° F) respiration declined rap-
idly after cutting, but at low temperatures it declined only slightly at
first and then was maintained at a fairly constant rate.

ACKNOWLEDGMENTS

The writers wish, to express their appreciation to various individuals
connected with shipping organizations, precooling agencies, and refrig-
erator-car companies who gave valuable assistance in these investi-
gations.

9m-4,'36