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12
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 surface.

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 the plant.

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 spaces.

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 of air.

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 Figure 7-2).

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 be known:

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 be known:

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 low level.

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 0.41.

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
123,200 Btu
Latent heat removed
during freezing is
408,000 Btu
Heat removed from 32
degrees to 15 degrees F is
27,880 Btu
------------
Total heat removed is 559,080 Btu

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 stored.

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
Food Specific
Heat
Above
Freezing
Latent
Heat
Specific
Heat
Below
Freezing
Percent
Water
Bacon0.5028 0.3020
Beef 0.77 1020.4172
Fish, fresh0.82 110 0.43 76
Lamb0.81 950.6767
Pork, fresh0.51 65 0.3046
Pork, salt0.46 15*12
Poultry0.80 85 0.4260
Veal0.70 89 0.39 63

*Will not freeze at normal freezing temperature because of salt content.

PROPERTIES OF DAIRY PRODUCTS
Food Specific
Heat
Above
Freezing
Latent
Heat
Specific
Heat
Below
Freezing
Percent
Water
Butter0.64150.3410
Eggs0.761050.4073
Oleomargarine0.65140.359
Ice Cream0.78960.4567
Cheese0.6450*35
Milk0.90127*87
Buttermilk0.92131*91

*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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