United States Department of Agriculture
Agricultural Research Administration
Bureau of Plant Industry, Soils
and Agricultural Engineering
Florida Agricultural Experiment Station
PREPACKAGING SWEET CORN AT PRODUCTION
AREA IN FLORIDA
Ventilated shipping carton containing 12 trays of prepackaged sweet corn
H. A. Schomer, R. K. Showalter, H. W. Hruschka, L. H. Halsey,
and Morris Lieberman
The project was carried out under the provisions of the Research and Marketing Act of 1946 and
was undertaken Cooperatively by:
Florida Vegetable Prepackaging Council
Paul B. Dickman, President
LaMonte Graw, Secretary
United States Department of Agriculture
Agricultural Research Administration
Bureau of Plant Industry, Soils and
H. A. Schomer, Physiologist
H. W. Hruschka, Assistant Physiologist
Morris Lieberman, Assistant Physiologist
Florida Agricultural Experiment Station
R. K. Showalter, Associate Horticulturist
L. H. Halsey, Assistant Horticulturist
Summary ......................................................................................... 4
Introduction .................................................................................... 5
Adequate Refrigeration Essential to Good Quality ................................. 6
Preparation of the Corn for Prepackaging .............................................. 6
Harvesting and Handling ............................................................... 6
Precooling ................................................................................. 8
Prepackaging ............................................................................. 9
Refrigeration and Shipping .................................................................. 11
Cold Storage for Precooling .......................................................... 11
Shipping in Trucks ..................................................................... 13
Condition of Corn at Destination .......................................................... 19
1. Sweet corn grown and prepackaged in Florida was received in satisfactory condition in distant
2. After pulling in the field the corn was hauled to the packing shed, quickly husked, and precool-
ed in the hydrocooler and cold storage to reduce loss of sugar.
3. The water temperature in the hydrocooler was about 400F. and the corn temperature was lower-
ed approximately 30 degrees during the 13 minutes in the cooler. The temperature of the corn
after hydrocooling was generally 500 to 600. A longer period in the hydrocooler together with
lower temperature of the water is needed at this stage in order to reduce the corn temperature
to a satisfactory level.
4. Since the corn had a temperature higher than that desired further cooling was attempted in cold
storage. However, this method was not satisfactory because of the slow rate of cooling due to
insulation of the packages and the relatively high temperature maintained in the cold room.
5. During transit no cooling occurred in the iced trucks except in one instance, while there was
substantial cooling in 3 of the 4 mechanically cooled trucks. The average arrival temperatures
were 50.40F. for the former group and 43.70 for the latter. Air circulation was poor in all the
trucks used as was indicated by wide variations in temperature in different parts of the load.
6. Rapid precooling to 320 350F. and maintenance of these temperatures would result in corn of
far superior quality.
PREPACKAGING SWEET CORN AT PRODUCTION
AREA IN FLORIDA IN 1948
One of the principal questions to be answered about prepackaging fresh fruits and vegetables
is: Where can it best be done? Should fruits and vegetables be prepackaged at the point of produc-
tion or at the terminal market? Sweet corn, grown during the winter months in Florida, canbepack-
aged there and shipped to distant markets, arriving in prime condition if adequate refrigeration
is provided all along the line. This conclusion is based on the resultsot one year's investigations
conducted jointly by members of the Bureau of Plant Industry, U. S. Department of Agriculture,
and the University of Florida Agricultural Experiment Station, in cooperation with the Florida
Vegetable Prepackaging Council. The work was done under a Research and Marketing Administra-
tion Project entitled, "Quality Preservation in Prepackaged Fruits and Vegetables", and under
a Florida Agricultural Experiment Station Project entitled, "Consumer Packaging of Vegetables
at the Shipping Point." The investigations were conducted at the Paul B.Dickman Farms, Ruskin,
Florida. Mr. Dickman furnished all the packing house facilities and the produce for the studies.
Cooperating also were Wallace and Tiernan Company, Inc., O. B. Andrews Company, E. I. du Pont
de Nemours and Company, Sylvania Industrial Corp., Celanese Plastics Corp., Goodyear Tire and
Rubber Company, Hayssen Manufacturing Company, Miller Trailer Company, and Carver Refrigera-
Florida sweet corn at Ruskin is ready for market in April, May, and June of each year. Since
corn is not produced in northern areas at this season, there is no competition from locally-grown
corn and consequently Florida corn can command a good price. However, transportation over con-
siderable distances to northern markets is necessary, and this involves many problems if the high
quality of the product is to be maintained.
The handling practices described in these investigations were farmore desirable than the usual
methods of handling bulk sweet corn. Good quality cannot be maintained without quick cooling
after harvest, and the corn must be held at low temperature until it is consumed. Prepackaging
operations at production areas offer the opportunity for quick and efficient cooling of husked ears,
which must be accompanied by thorough refrigeration in shipping. Husking the corn at the place of
production also allows for utilization of waste. Ears unfit for sale, together with the husks and
trimmings, can be utilized for stock feed, or added to the soil in various forms as compost or
fertilizer. In addition, the 3-inch "servings," which are packed crosswise in the consumer pack-
age, may be cut from ears that are of good quality but were partially damaged or improperly filled,
the undesirable portions being trimmed off. Such damaged ears normally would be thrown away in
retail channels. There is also a big saving in transportation costs. It is estimated that one truck
load of prepackaged corn is about equivalent to three truck loads of crated bulk corn when allow-
ances are made for waste in husking and trimming, and for tonnage of ice and top ice in the bulk
loads. The prepackaged loads are welcomed by handlers because of the light, convenient sized
packages, and the absence of water and ice which are a feature of the usual bulk loads.
The film and carton used in packaging protects the tender kernels of the husked corn from
injury and from dehydration. However, it must be emphasized that all of the care and costs expend-
ed in delivering good quality corn to the market can quickly be dissipated by improper handling
in wholesale and retail channels. It is as important to maintain adequate refrigeration and care at
the consumer level as at the production, packing, and shipping levels.
ADEQUATE REFRIGERATION ESSENTIAL TO GOOD QUALITY
Quality of sweet corn depends largely upon the amount of sugar present in the kernels. Tender-
ness and consistency of the kernels are used to determine the proper picking maturity, at which
time the sugar content is near the maximum. This sugar disappears very rapidly after the corn is har-
vested unless it is quickly cooled toa temperature below 400F., preferably 320. In a study of sugar
loss from sweet corn during consecutive periods of storage at different temperatures, Appleman and
Arthurl/ found that 3.5 per cent of the sucrose was lost in 24 hours at 320, while during the same
period at 860 the loss was 59.4 per cent. Figure 2 shows a graph of their results with corn stored
at 320, 500, 68, and 860F., for periods of 24, 48, 72, and 96 hours. While 21 per cent of the suc-
rose had disappeared after 96 hours (4 days)at 320,60.5 percent had disappeared at 500, and 70.2
per cent at 860. From these figures it can be seen that if corn of good quality is to reach the con-
sumer, it must be adequately cooled from the time it is pulled until it is sold by the retailer.
PREPARATION OF THE CORN FOR PREPACKAGING
Harvesting and Handling
The sweet corn described in these studies was pulled in the field by crews of 5 pickers and
tossed into trailers which were pulled with light farm tractors. A trailer load was made up of the
corn obtained from one trip through the field which required about 15 minutes. It was immediately
hauled to the packing house (Figure 3) where it was quickly unloaded onto a moving belt which
carried the ears to the husking machines. After the husks were removed the corn was fed onto a
trimming belt where sorters trimmed the ears and placed them on moving belts which carried them
to rotary knives (Figure 4). Here they were cut to standard lengths, either 3 inches or 5 inches,
depending upon the suitability of the ears for either length.
10 32 F
Figure 2.--Depletion of sucrose
20- in sweet corn during consecutive
24-hour periods of storage, ex-
30 pressed as percentages of the
initial sucrose in the corn,which
40 F was 3.87 per cent, wet weight.
40 *500 F
60 680 F
90 / Appleman, Chas. O., and
John M. Arthur. Carbohydrate
Metabolism in Green Sweet Corn
10024 48 72 96 During Storage at DifferentTem-
HOURS peratures. Jour. Agr. Res. 17;
Figure 3.--Light farm tractors
pull trailer-loads of corn to the
packing shed (above). Trailers
are unloaded onto a moving belt
which carries the ears to the
husking machines. (right)
Figure 4.--Trimming and grading belt showing rotary knives for cutting ears
to lengths of 3 or 5 inches.
The prepared ears of corn then moved onto the slowly moving belt of the hydrocooler. The
hydrocooler was a tunnel 30 feet long in which cold water showered down on the moving belt from
perforated metal trays near the top of the tunnel (Figure 5).
Figure 5.--Hydrocooler showing opening into tunnel (foreground) and chlorinator at left.
The temperature of the water varied from about 360 to 46F., depending upon the amount of
corn being cooled. Greater capacity of the cooling system was needed to prevent a rise in tem-
perature of the water when increasing volumes of corn were in the hydrocooler. The cooling wa-
ter was re-circulated and chlorine was added to the water to control bacteria and fungi in it. The
corn remained in the hydrocooler for about 13 minutes during which time it was cooled approxi-
mately 30 degrees.as shown in table 1. This amount of cooling was not as much as was desired
since the corn being brought from the field had cob temperatures that were usually in the 800 to
900 range. After precooling, the cob temperatures ranged from 480 to 590 and therefore were still
much above the recommended maximum of 400.
Thirty-six degrees was considered by the refrigeration engineers who installed the precooling
equipment to be the lowest temperature obtainable for the water in the hydrocooler. Ice formation
on the cooling coils prevented cooling of the hydrocooler water to lower temperatures.
Since the corn was not being cooled to the proper temperature, studies were made to determine
the length of time the corn should remain in the hydrocooler and still get efficient cooling. A wire
mesh basket was hung within the tunnel beneath the shower and within reach of the open end of
the tunnel. Thermocouples were inserted within cobs of four ears taken from the sorting belt just
before they entered the hydrocooler. The temperature of the water in the hydrocooler was 38.50 at
the beginning of the test, and 36.20 at the end, 30 minutes later. These temperatures were as low
as could be maintained during a day's run and were 4 or 5 degrees lower than was ordinarily
maintained. After the temperatures of the 4 ears were taken, they were placed in the bas-
Table 1.--Summary of temperature changes in ears of corn throughout the prepackaging process 1/.
Test Temp. of Air temp. Corn temp. HYDROCOOLER 13 MINUTES Temp. Temp. Temp. rise Final Net
No. corn from in packing before Water Corn temp. Amount rise in rise on during temp. lowering
field house entering temp. after of acid packing wrapping & after pack- of temp.
cooler cooling cooling dip belt heat sealing aging
oF. OF. OF. OF. OF. OF. OF. oF. OF. OF. OF.
1 84.6 74.0 83.4 46.0 57.9 25.5 1.3 1.8 1.5 62.5 22.1
2 85.2 80.5 85.6 42.5 52.4 33.2 2.6 3.8 2.3 61.1 24.1
3 82.6 81.8 82.6 42.5 48.3 34.3 52.3 30.3
4 87.8 82.0 88.2 42.5 58.7 29.5 -1.9 1.9 0 58.7 29.1
5 84.6 83.0 84.8 40.0 50.2 34.6 3.9 2.3 56.4 28.2
6 85.8 87.0 85.8 41.0 53.2 32.6 -
/ All corn temperatures were obtained by inserting thermometers or thermocouples well within
the center of the cob.
ket with other ears of corn stacked four layers deep.' One of the test ears was placed in each
layer. The ears, which entered the hydrocooler at temperatures from 82.10 to 86.60F. and aver-
aged 83.70, cooled at about uniform rates in the various positions within the basket (Figure 6).
During the first 10 minutes they cooled to 61.20 or 22.5. After 20 minutes the ear temperatures
averaged 46.40, a cooling of 15 degrees during the second 10-minute period. The rate of cooling
fell off considerably during the third 10-minute period, in which the average temperature dropped
less than 6 degrees. (Table 2). As a result of this test, it is apparent that the corn should be pre-
cooled in the hydrocooler for a minimum period of 20 minutes to secure optimum cooling when the
water temperature is from 360 to 380F.
During a similar test when the temperature of the water in the hydrocooler was 420 to 430F.,
the average ear temperature was lowered from 86.60 to 67.20 in 10 minutes and to 52.50 in 20
minutes (Table 2). These temperatures, when compared with the 61.20 and 46.40 obtained in cool-
ing in 360 to 380 water for 10 and 20 minutes, respectively, emphasize the value of low tempera-
tures of the cooling water.
After the corn was precooled it warmed up several degrees during the packaging operations.
From the precooling tunnel the corn moved to the packaging belt where the ears were placed in
cardboard trays, 5 in. x 314 in. x 1% in. Three 5-inch ears were placed lengthwise in a tray, 2 ears
in the bottom layer and one on top, or five 3-inch ears were placed crosswise in the tray, 3 in the
bottom layer and 2 on top.
The trays of corn were then over-wrapped and heat-sealed with 300-MSAT-86 cellophane by an
automatic wrapping machine equipped with a perforator. The film on the top of each tray wasper-
forated with a /-inch hole to allow for air exchange. After wrapping, 2 layers of 6 packages each
were placed in each master carton (as shown in Figure 1 on cover), which was then run immediate-
ly into cold storage on a conveyor. The master cartons were well ventilated, having 28 one-inch
Figure 6.-Rate of cooling of husked Golden Cross Bantam sweet corn in hydrocooler. Temperature
of cooling water::38.50F. at start; 36.20F. at end.
5 10 15 20 25 30
TIME IN MINUTES
holes around the sides, incomplete closures
2 inches square, and ventilated dividers.
on top and bottom which left air spaces approximately
Complete temperature records throughout husking, handling, and packaging are summarized in
table 1. The net amount of cooling throughout the entire process on five different packing dates
varied from 22.1 to 30.3 degrees F.
The entire process from field to cold storage required approximately 45 minutes. Prepackaging
as described in these studies thus had a distinct advantage over regular handling methods since
the corn was pulled, husked and precooled within a very short time. However, efficient cooling
to lower temperatures than those obtained is desired for high quality.
Table 2.--Temperature readings at 10-minute intervals for husked Golden Cross Bantam Sweet
Corn during precooling in a wire basket within the hydrocooler for a 30-minute period.
Test Minutes Temperature Temperature of Ears of Corn
No. in of water Top 2nd 3rd 4th (bottom) Average
Cooler Layer Layer Layer Layer
1 0 38.5 82.1 83.9 82.1 86.6 83.7
10 38.5 60.0 62.1 62.1 60.6 61.2
20 38.0 46.1 46.8 46.7 45.9 46.4
30 36.2 40.8 41.1 40.7 40.7 40.8
2 0 42.0 86.6 88.3 84.3 -- 86.6
10 42.0 67.0 69.5 65.0 -- 67.2
20 43.0 52.5 54.5 50.5 52.5
REFRIGERATION AND SHIPPING
Cold Storage for Precooling
Since the hydrocooler did not have sufficient capacity to precool the corn to the desired tem-
perature, further precooling in cold storage was needed. Temperatures of the cold room varied
between 350 and 400F., depending upon the amount of corn being placed in the room (Figure 7).
The corn entering the cold room in the shipping cartons had a temperature range of approximately
500 to 60F. Both the consumer package and shipping carton act as insulators and greatly retard
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the rate of cooling. In order to quickly cool the corn to temperatures of 40or below, air temperatures
below the freezing point of water are necessary. Since the freezing point of sweet corn averages
slightly below 290F., the cooling rooms may be safely held at temperatures several degrees below
the freezing point of water.
A test was run in which rates of cooling of corn with and without husks and within packages
were determined in the cold room. The results are shown in figure 8. Temperature of the corn from
the field was approximately 820F.
-LOTS 2 AND 3
2 4 6 8 10 12 14 16 I
HOURS IN COLD STORAGE
Figure 8.--Rates of cooling in cold storage of various lots of sweet corn that have had the follow-
1. Regular run: husked, precooled in hydrocooler, prepackaged with cellophane over-
wrap, and placed in shipping carton;
2. Husked, precooled in hydrocooler and cooled further in wire basket in cold room for
3 hours then prepackaged as in 1;
3. Husked and placed directly into cold room in wire baskets;
4. Unhusked and placed directly from field into cold room;
5. Air temperature in cold room.
Some of this corn in wire baskets was placed directly into the cold storage room without being
husked. The other lots were husked and trimmed, and one lot in wire baskets was placed directly
from the trimming belt into the cold room. The other two lots were cooled in the hydrocooler after
which one was placed in wire baskets and into the cold room and the other lot was prepackaged as
was done commercially. All of the lots placed in the cold room were placed in line with the cool-
ing fans where they received maximum cooling.
In figure 8, line 1 represents the regular commercial run, the corn entering cold storage it
530F., which was a net cooling, after packaging of 29 degrees (from 820 to 530). Line 2 represents
the husked precooled lot which was cooled in the hydrocooler to about 480 and placed directly
into cold storage. The 5 degree higher temperature of lot 1 is due to heating during prepackaging.
Lot 3, which was husked and placed directly in the cold room, required 50 minutes to reach 480,
the temperature of the hydrocooled lot. The unhusked corn cooled less rapidly and reached 480
after 6 hours. Thus most efficient cooling was obtained in the hydrocooler where the corn was
cooled to 480 in 13 minutes.
During packaging this temperature was raised approximately 5 degrees F., and after 18 hours
in the cold room the temperature of the corn within the package was still nearly 44. More satis-
factory temperatures were obtained in the lot which was hydrocooled and further precooled in the
cold room for 3 hours before packaging. The minimum temperature reached in this lot was approx-
imately 340, at which temperature it was packaged. During prepackaging the temperature of the
corn rose to 420, and during the next 13 hours in the cold room the corn had cooled to only 390.
Figure 8 shows that the rate of cooling is greatly reduced by packaging, and that little cooling
can be expected after the shipping cartons are placed in cold storage at the temperature that pre-
vailed during this test. Therefore precooling to the desired temperature should be obtained before
packaging. If hydrocooling does not accomplish this, additional cooling is necessary.Undoubtedly
more rapid cooling and lower temperatures of the produce would have been obtained if the cold
room temperatures had been held near 300F.
Shipping in Trucks
All shipments were made in refrigerated trucks to both near and distant markets. Distant ship-
ments were made to Baltimore, Philadelphia, New York, Boston, Detroit, St. Louis, and Chicago.
These loads required constant refrigeration during the transit periods which ranged from 35 to 54
The trucks were both single-unit and tractor-trailer types and had either built-in bunkers for
ice or attached units for mechanical cooling (Figure 9). It was soon learned that in the iced trucks
ice alone did not give adequate refrigeration. The addition of five per cent of salt was recommend-
ed for greater cooling, and was used in subsequent shipments. Since no salt was obtainable at
many of the icing stations, it was necessary to carry bags of salt along with the loads. The iced
trailers were 24 feet long, insulated on sides and top with 2 inches of fiber glass, an innerlayer
of 4-inch plywood, and an additional layer of 25/32-inch celotex. The floors had 2 inches of wood,
a covering of asphalt, and one inch wood strips to permit air circulation. Each trailer contained a
bunker with a capacity of approximately 2100-2400 pounds of ice. The bunker was situated in
front and had a fan at the top center.
The mechanically refrigerated trucks were of three sizes : a 14-foot panel type, a 30-foot trailer,
and a 34-foot trailer. Insulation on the panel type consisted of 2 inches of fiber glass and a lining
of plywood. The 30-foot trailer had the same type of insulation as the 24-foot ice trailers. The
34-foot trailer had four inches of fiber glass and a lining of plywood. All had wood strips on the
floor to permit air circulation. These trucks were cooled by Thermo-King units: the 34-foot trailer
by Model 1D-10 and the others by Model EH.
Figure 9.-Refrigerator trucks used in hauling prepackaged sweet corn to market. Above two
trailer trucks with mechanical cooling units. Below trailer truck with ice bunker and
Twenty-five test shipments of corn were made to distant markets in the spring of 1948, and
complete records of the condition and temperature at start, enroute, and at the final destination
were obtained. Practically all shipments arrived in acceptable condition and were well received
on the markets. The general results on ten such test shipments are herein reported.
An attempt was made to cool the corn to at least 400F. before loading for shipment. Since this
temperature was not obtained in the hydrocooler, the corn was generally held overnight in the cold
room for further cooling. Often the temperature of the cold room was not sufficiently low to obtain
the proper cooling even with this practice. In addition, the market occasionally demanded quick
delivery, in which instances the corn was not cooled at all after packaging. All these factors con-
tributed to product temperatures much above those recommended (Table 3).
Before loading, the trailer was usually precooled, then backed up to the door of the cold room
and the shipping cartons were loaded by mechanical conveyors. The 24-foot trailers carried ap-
proximately 1200 cartons and the 30- and 34-foot trailers approximately 1500 to 1600 cartons. The
cartons were stagger-loaded to allow for air circulation around them (Figure 10). The load was
usually 6 cartons wide, 9 high, and 23 to 30 long. The space between cartons was approximately
3 inches wide. Shifting of the load in transit was negligible. The temperature records of the test
loads were obtained with 12 electric resistance thermometers attached to a main cable. Each ther-
mometer was in a selected position in the load. Nine of the resistance thermometer "bulbs" were
inserted into packages, located in the top, middle, and bottom layers of the first, center, and rear
tiers, either in centerline or side positions. The other 3 thermometers were located so as to obtain
the temperature of the cold air from the fan blower at top front centerline, of the return air at the
bottom front centerline, and of the rear top air. Three recording thermometers were also usedinside
cartons in the top, middle, and bottom layers of the center tier, to obtain continuous temperature,
records. Another thermograph was fastened beneath the truck to obtain a continuous record of out-
side air temperature. Temperature readings at the 12 positions in the truck were taken at conven-
ient intervals by an observer who rode the truck.
In table 3 the data from the ten tests are summarized. Of the 10 test loads, 6 were in iced
trucks and 4 in mechanically refrigerated trucks. From these data it can be seen that in only 4
tests were the average commodity temperatures lowered in transit. Three of these were in trucks
refrigerated mechanically. In the fourth truck with mechanical refrigeration, test number 7, only
0.4 of a degree was gained during the 44 hours in transit. In the other 5 shipments, in which the
average temperature rose during transit, the amounts of rise were 0.5 1.9, 2.1, 2.2, and 3.9
degrees, all in iced trucks. In every case, except one, where the difference between the average
cooling blast in transit and the initial average commodity temperature was greater than 8 degrees
there was a lowered final average corn temperature. The larger the spread between the average
initial commodity temperature and the average cooling blast, the greater the amount of cooling. An
exception was in test number 7, in which the initial temperature was 39.90 and the cooling blast
was 30.9, yet the final average temperature increased 0.4 of a degree.
In 4 of the 6 iced trucks the average cooling blast was higher than 47OF. This temperature
was very high for the cold air, which should have been near the freezing point. The explanation
for this is that air leakages occurred into the upper portion of the bunker and the air blown over
the top of the load was not all drawn through the ice. In test number 5, the cooling blast averaged
51.70, and at no time in transit was it lower than 48.70, although temperatures near 300 could be
expected with such a mixture of ice and salt. The lowest package temperature in the load, at any
time, was 470 and the temperature of mostpackages was considerably higher.
Ave. Ave. Ave. Diff. Ave. Ave. Diff.
Type Hours Ice Salt temp. temp- temp. between corn corn between
Test of in used Used out- of of cold air temp. temp. cold air
No. refriger- transit (lbs.) (lbs.) side cooling return blast & at at blast &
ation air blast air air re- start desti- ave.
turn (after nation carton
OF. OF. OF. OF. OF. OF. oF.
1 Ice 51 6300 100 71.2 47.4 52.8 5.4 55.6 51.9 8.2
2 Ice 35 7650 100 67.2 47.6 58.8 11.2 51.8 54.0 4.2
3 Ice 54 10500 500 78.1 39.3 47.4 8.1 44.3 46.2 5.0
4 Ice 48 6474 100 79.2 47.5 49.8 2.3 45.0 49.2 2.5
5 Ice 41 7200 700 78.3 51.7 54.2 2.5 52.6 54.7 0.9
6 Ice 54 9300 400 80.2 43.9 48.5 4.6 46.5 47.0 2.6
7 Mechanical 44 -- 76.2 30.9 42.4 11.5 39.9 40.3 9.0
8 Mechanical 45 -" 75.5 31.5 46.2 14.7 43.0 40.3 11.5
9 Mechanical 42 -- 79.4 33.3 54.5 21.2 53.5 46.7 20.2
10 Mechanical 38 83.8 40.2 50.3 10.1 50.0 47.3 9.8
Table 3.--Summary of refrigeration records of ten truck loads of prepackaged sweet corn shipped
from Ruskin, Florida, to various distant markets and the flavor upon arrival at destination.
Minimum transit temperatures Maximum transit temperatures Temperature spread Net cooling Corn
At start At destination At start At destination between coldest and or heating flavor
warmest positions in of load. at
OF. Position OF. Position OF Position OF. Position load. desti-
Start Desti- Gain or
OF. cr. OF. OF.
50.0 Middle tier 46.0 Middle tier 60.0 Front tier 55.5 Front tier 10.0 9.5 .5 -3.7 Fair -
bottom top center center lacks
41.8 Middle tier 48.5 Rear tier 64.5 Rear tier 58.5 Front tier 22.7 10.0 -12.7 2.2 Fair -
top top bottom center lacks
39.2 Middle tier 43.8 Middle tier 48.5 Middle tier 49.7 Front tier 9.3 5.9 3.4 1.9 Good
bottom, side top, side middle, side bottom
37.7 Middle tier 41.2 Middle tier 51.0 Middle tier 55.0 Middle tier 13.3 13.8 .5 3.9 Good
top top bottom, side bottom
48.5 Middle tier 50.3 Middle tier 61.0 Rear tier 59.3 Middle tier 12.5 9.0 3.5 2.1 Fair
middle, side top, center top bottom
40.0 Bottom bunker 39.0 Rear tier 57.0 Front tier 56.0 Middle tier 17.0 17.0 .0 0.5 Good
top top bottom, side
33.8 Middle tier 35.2 Middle tier 52.0 Rear tier 50.5 Front tier 18.2 16.8 1.4 0.4 Very good
middle, side top top center
40.0 Middle tier 36.0 Middle tier 44.2 Rear tier 46.5 Front tier 4.2 10.5 6.3 -2.7 Good
bottom, center top top bottom
47.0 Middle tier 29.0 Middle tier 62.0 Rear tier 65.0 Middle tier 15.0 36.0 21.0 -6.8 Good
bottom, center top bottom bottom, center
44.0 Middle tier 41.8 Middle tier 61.5 Rear tier 56.1 Front tier 17.5 14.3 3.2 -2.7 Good
bottom top top bottom
Figure 10.--Shipping cartons of prepackaged sweet corn were stagger-loaded to allow for air
From table 3 it is noted that generally there is a considerable difference in temperature at
time of loading between the warmest and the coolest cartons. This temperature spread varied in
the different loads from 4.2 to 22.7 degrees. With efficient air circulation in the trucks the pack-
age temperatures should have become equalized so that there would have been little difference in
temperature between packages at the end of the transit period. Actually little equalization occur-
red. In test 10, for example, the spread between the maximum and minimum temperatures of the car-
tons in the load rose 15 to 36 degrees during 42 hours in transit. The coldest carton in the load cool-
18 degrees from 470 to 290F., while the warmest rose 18 degrees from 470 to 650F. These results
demonstrate that there was poor circulation of air throughout the load, and this allowed the tem-
perature of areas within the trucks to remain high and, in some cases, to rise during transit. Im-
provement must be made of the air circulation systems in the trucks and probably of the method of
loading to insure satisfactory transit temperature.
The mechanically refrigerated trucks delivered the corn at more satisfactory temperaturesthan
did the iced trucks. Average final temperature of the 4 loads in the former were 40.30, 40.30,
47.00, and 47.30F., with an over-all average of 43.70, while the temperature in the latter aver-
aged 51.90, 54.00, 46.20, 49.2, 54.70, and 46.70, with an over-all average of 50.40F. With effi-
cient air circulation the mechanically refrigerated trucks would have delivered the corn at very
satisfactory temperatures, since the cooling blast temperatures averaged 30.90, 31.50, 33.30, and
40.20 during transit. Mechanical trouble during part of the trip in the fourth shipment was the
cause of the higher cooling temperature for that load. In some instances the temperature of the
cold air blast was as low as 200. The minimum temperatures in these loads were in cartons near-
est the cold air blast and were 34.20, 35.60, 38.00, and 41.80, averaging 37.60, while the maxi-
mum temperatures were 48.70, 49.60, 56.00, and 56.10, with an average of 52.60. The cooling
system in these trucks was not properly designed for efficient cooling of the entire load, since
there was little separation between the warm-air intake and the cold-air duct. Proper design would
have insured warm air intake from the bottom of the load only, with the cold air blowing the full
length over the top of the load.
The cooling blast temperatures of the 6 iced loads averaged 47.40, 47.60, 39.30, 47.50, 51.70,
and 43.90, with an over-all average of 46.20F. The average final minimum temperatures of the
iced truck loads was 45.50 and the maximum temperatures averaged 55.40.
The difference between the cooling air blast and the return air is an indication of the amount
of heat removed from the load. This difference was considerably greater in the mechanically
cooled trucks than in the iced trucks, the averages being 14.4 degrees and 5.7 degrees respec-
tively. In the iced trucks the air was obtaining relatively little cooling from the bunker of ice and
salt as is evidenced by the temperatrues of the cooled air blast and the return air.
In summing up the studies of the truck shipments, it is apparent that there were several rea-
sons why the corn was not delivered to the destinations at temperatures lower than were obtained:
(1) Insufficinet precooling before loading into trucks; (2) poor air circulation within the truck or
trailer bodies; (3) unsatisfactory cooling of the air blast by the ice and salt within the bunkers of
the iced trucks. Also, the method of stacking cartons within trucks may not have been best for
efficient cooling; but no variations were tried on methods of loading. All of these phases of truck
shipment need further investigation and improvement.
CONDITION OF CORN AT DESTINATION
The corn generally arrived at destination in good condition, as determined by appearance and
flavor. Corn in loads 1, 2, and 5 was judged only fair because it was lacking in sweetness. In
these loads the corn temperatures were above 500F. at loading and at destination. Some of the
corn in load 2 had a.slightly sour odor at destination, and was not placed in retail channels. The
sourness was not detectable after the corn was cooked, and may have been due to an acid dip that
the corn was receiving at that time. This dip was discontinued later when it was found to have
little or no effect in preventing discoloration of the kernels. Discoloration was effectively con-
trolled by proper refrigeration alone. However, although the corn in these three loads appeared
attractive, it lacked sweetness due to the high temperatures at which it was kept after harvest.
Corn in load 7 was the only lot that was rated very good at destination. This load averaged
39.90F. after loading and was the only load that was precooled within the recommended range. Un-
doubtedly the high quality of the corn was due largely to this early precooling. The cold tempera-
ture was maintained in transit, the arrival average temperature being 40.30. These were the low-
est temperatures obtained in any of the shipping tests.
Corn of the remaining 6 loads was rated good, and this corn was well received by retailers.
It was all delivered in the 400 to 500F. range. Lower temperatures would have insuredbetter
quality to the consumer.