STOWAGE OF FOODS
A. GENERAL PRINCIPLES|
12A1 Classification of foods. In long-term
cold storage of foodstuffs, great care is taken
to maintain air temperature at the degree best
suited to each kind of food, and many different
rooms with varying temperatures are required.
However, in a submarine this would be
impractical. Moreover, the storage is for short
terms only when the requirements for preservation are not so strict. For submarine storage,
foods may be classed in three main groups
1) meats, including poultry and fish; 2) dairy
products; and 3) vegetables, including fruits.
12A2. Temperature requirements in food
storage. Meats, poultry, and fish are best kept
at temperatures below 32 degrees F; dairy products,
vegetables, and fruits, at a temperature a few
degrees above freezing. Bananas are an exception among fruits, as they cannot be kept at
temperatures below 55 degrees F. Oranges, lemons,
grapefruit, tomatoes, and melons also must be
stored at a temperature around 50 degrees F.
Meats are stored by two methods: 1) cooler
storage, and 2) freezer storage.
Cooler storage has a temperature slightly
above freezing. It is a method which needs
careful watching and control of humidity and
ventilation. Meat for current consumption is
stored at 36 degrees F to 40 degrees F.
Freezer storage may be either near freezer
storage with temperatures around 27 degrees F, or
sharp freezer storage with temperatures
around 10 degrees F. This is always necessary for
long-term storage, since at temperatures below
10 degrees F, most bacteria and molds cannot grow.
Meats frozen at this temperature are always
preserved in best conditions of appearance,
tenderness, and flavor. At 10 degrees F, meats may
be preserved for several months, while at 27 degrees F
there is some bacterial growth on the surface
within 30 days. Poultry and fish should be
sharp frozen. After being frozen, fish should be
dipped in salt water for a few minutes in order
to form a slight layer of salt-ice over the
12A3. Humidity requirements in food storage.
While most persons know that food is
preserved by being kept in a cold place, it is
not so well known that the humidity of the air
is also a major factor in proper storage. Foods
contain a large percentage of water, and they
evaporate moisture just as human beings do.
In general, about 60 percent of the weight of
meats is the result of their water content.
Vegetables and fruits contain from 80 to over
90 percent water. Dairy products are more
variable: butter contains only about 10 percent
water, cheese 35 percent, eggs 73 percent, and
milk 87 percent.
If vegetables and fruits were stored in fairly
dry air, they would wilt and become worthless
quickly, for moisture evaporates from them
constantly (except the citric acid fruits, from
which moisture evaporates slowly). However,
the storage room air is not likely to be dry,
and the very fact that moisture evaporates
constantly from these foodstuffs makes up for
the loss of moisture in the air resulting from
condensation by the refrigeration process. Thus
they themselves keep up a fair balance. In
addition, fruits and vegetables can and do
absorb moisture, which helps prevent wilting.
Meats, however, cannot absorb moisture, and
once too much evaporation has taken place, a
permanent shrinkage and loss of weight result.
The flavor, too, is greatly impaired. On the
other hand, if too little evaporation from meats
takes place, because of a high (92 percent or
over) relative humidity of the air, two deleterious conditions arise. One is called sliming,
and is brought about by excess moisture on
the surface from the meat juices. The other is
sweating, from the condensation of air moisture on the surface. Either of these two conditions is favorable to the growth of bacteria
and results in spoiling of the meat.
Meats keep best at relative humidities of
from 85 to 90 percent.
Another objectionable condition eventually
appears after a considerable storage period,
even if the humidity of the air is maintained
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at the best level. This condition is the growth
of molds, a group of tiny plants known also as
fungi. However, molds grow chiefly on the
surface, in contrast to bacteria which spread
all through the meat. If molds are cut away,
the rest of the meat remains in good condition.
If molds appear on meat, the mold growth
below the surface is about equal to the height
of the molds above the surface, and the meat
should be trimmed away sufficiently to remove
all of the subsurface growth. But molds do not
grow if the meat is stored at temperatures
considerably below freezing.
If sterilamp tubes are available, they are a
decided advantage in the cold storage of food
stuffs. Over 80 percent of the radiation of these
lamps is in the ultraviolet region and acts as
an effective germicide and fungicide. Food
stuffs may therefore be stored at considerably
higher temperatures without deterioration,
which results in more economical operation of
12A4. Ventilation requirements in food storage. In addition to the requirements of proper
temperature and humidity, there is also the
matter of proper ventilation. Foods need ventilation to be preserved well, just as people need
it for comfort. If the air becomes stagnant,
a blanket of high relative humidity is built
up, thus preventing necessary evaporation.
12A5. Correct storage of food. Foodstuffs
must be stowed in such a way that space is
left for air circulation. This requires attention
to two points. First, the boxes, cartons, or
sacks must not be piled up solidly in large
stacks, but rather in rows or small stacks with
some air space between them. Moreover, if
foodstuffs are piled solidly in large stacks, the
outer layers of such stacks act as insulation,
so that the interior parts of the stacks cannot
be cooled. Second, all the rows of small stacks
should be placed in the same direction, in order
to follow the natural circulation of air in the
rooms and to avoid the formation of dead air
There is a natural inclination, when taking
on food supplies for a war patrol, to stack
them closely, in order to carry as much as
possible. Nothing is gained in doing this, if
subsequently a large percentage of the food
must be thrown out because of spoilage.
Portable electric fans may be placed in the
food storage rooms to assist in the circulation
12A6. Prevention of odors in food storage.
A highly important factor in food storage is
the matter of odors. Butter and eggs are a
source of annoyance in this respect, for they
pick up foreign odors easily. They must never
be stored in the same room with cabbage, or
any other foodstuff having a pronounced odor.
12A7. Storage of quick-frozen foods. Quick
freezing of foods is a great advance in the
science of food preservation. The time will
come, no doubt, when all or nearly all food
stuffs will be prepared in this way. Not only
is the food kept more easily, but much more
food can be stored in a given space.
12A8. Food storage rooms in a submarine.
Only two rooms in a submarine are available
for cold storage of perishable foods. These are
the cool room, entered through a hatch, and
the refrigeration room, entered by a door from
the cool room. These two rooms have fully
insulated walls, floors, and ceilings (see
The cool room is maintained at a temperature of 40 degrees F, the refrigeration room at 15 degrees F.
Meats, poultry, and fish are stored in the refrigeration room. Vegetables, fruits, and dairy
products are stored in the cool room.
12A9. Cooling of drinking water. Water for
drinking is carried by a pipe leading from the
fresh water tank, through the cool room, to
scuttlebutts. It is chilled to a satisfactory
drinking temperature in the cool room.
B. COOLING OF FOODS|
12B1. Navy requirements on precooling. All
foodstuffs to go into cold storage in a submarine are expected to be delivered aboard
precooled. However, frequently food must be
taken aboard in a location where precooling is
not available. In such case, a considerable load
is placed on the refrigeration system in reducing the temperature of the foods to the proper
storage level. It is therefore important to know
what this load is in refrigeration tons so that
the refrigeration system may not be over
loaded. It is easily calculated, as follows:
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12B2. Method of calculating food cooling
loads. Case 1. Cooling foods to a temperature
not below freezing. The following values must
1. Weight of the food in pounds.
2. Temperature drop in degrees.
3. Specific heat of the food above freezing.
Multiplying these values gives the total heat
removed in Btu. Dividing by 288,000 gives the
number of refrigeration tons used (see Section 4B4).
Example. 400 pounds of tomatoes are received at 75 degrees F. They are to be cooled to 40 degrees F.
The specific heat of tomatoes is 0.95 and the
temperature drop is 35 degrees. Therefore:
((400 x 35 x 0.95) / 288,000) - .046 TR
Case 2. Cooling foods to a temperature
below freezing. The following values must
1. Weight of the food in pounds.
2. Temperature drop to 32 degrees F.
3. Specific heat of the food above 32 degrees F.
4. Latent heat of the food.
5. Temperature drop from 32 degrees F to desired
6. Specific heat of the food below 32 degrees F.
In this case, simply compute separately the
heat removed in the drop from the high temperature to freezing, in the drop from freezing
to the low temperature, and the latent heat
removed during the freezing; then divide the
sum of these by 288,000.
Example. 4,000 pounds of beef are received at 72 degrees F. The beef is to be frozen and
stored at 15 degrees F. The specific heat of beef
above freezing is 0.77 and below freezing is
4,000 X 40 X 0.77 = 123,200
4,000 X 102 = 408,000
4,000 X 17 X 0.41 = 27,880
|Heat removed from 72
degrees to 32 degrees F is
|Latent heat removed
during freezing is
|Heat removed from 32
degrees to 15 degrees F is
|Total heat removed is
Then 559,080/288,000 is 1.94 refrigeration tons.
This means almost four days full load on
the refrigeration system. It shows plainly
the necessity of obtaining precooled supplies,
for the refrigeration system is always well
loaded in taking care of supplies already
12B3. Specific heats of foods. In order to
make such calculations, it is necessary to
have a table giving the relevant data for various foods. In the following table, the specific,
heat below freezing is given only for such
foodstuffs as need to be stored at a temperature below 32 degrees F.
|PROPERTIES OF MEATS AND FISH|
|Beef|| 0.77|| 102||0.41||72|
|Fish, fresh||0.82|| 110|| 0.43|| 76|
|Pork, fresh||0.51|| 65|| 0.30||46|
|Pork, salt||0.46|| 15||*||12|
|Poultry||0.80|| 85|| 0.42||60|
|Veal||0.70|| 89|| 0.39|| 63|
*Will not freeze at normal freezing temperature
because of salt content.
|PROPERTIES OF DAIRY PRODUCTS|
*Should not be frozen. Fresh milk should be stored
at 35 degrees to 38 degrees F; never above 40 degrees F.
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12B4. Properties of fruits and vegetables.
These foodstuffs should not be frozen, as
freezing ruins them. The specific heat above
freezing of fruits and vegetables may be
taken as 0.90 for all practical purposes. These
foodstuffs contain a large percent of water:
green corn, 75 percent; potatoes, 80 percent;
and the others, from 85 to 90 percent.
12B5. Water content of foods. The percentages of water contained in foods as
shown by the property tables indicate the
considerable intake of water with foods, a
fact that is usually unnoticed.
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Copyright (C) 2004 Maritime Park Association
All Rights Reserved
Version 1.10, 22 Oct 04