WHY FOODS SPOIL.—Most foods spoil or change readily,—fruits decay, milk sours, butter becomes rancid, and meat putrefies. Knowledge concerning the spoiling of foods makes it possible for the housekeeper to preserve foods from one season to another; it gives her the assurance that her preserved fruit will "keep."

The decay of foods is due largely to the existence of minute vegetable organisms or microorganisms. These microorganisms are molds, yeasts, and bacteria. The molds (see Figure 88) are visible to the naked eye, the yeasts (see Figure 86) and bacteria (see Figure 89) are microscopic in size. These plants exist everywhere, and in everything (except those things in which the organisms have been destroyed and prevented from reentering),—in the air, in and on foods, and all over our bodies. Like all plants, these organisms require warmth, moisture, and food for their most rapid growth. Oxygen is necessary for the growth of some of these plants.

Many foods constitute nourishment for these organisms. It is because these plants exist in foods and live upon them that changes in foods result. The mold on bread and fruit, the odor from decaying meat and eggs, the liquefaction of decayed eggs, and the gas from fermenting canned fruit are caused by microorganisms existing and growing in these foods. The following experiments show the growth of molds on food and other materials:

EXPERIMENT 80: EFFECT OF AIR, LIGHT, AND DRYING UPON THE GROWTH OF MOLDS. —Place a piece of bread on a saucer. Allow it to remain uncovered, in a light place, at room temperature, for several days. Examine. What is the condition (moist or dry) of the bread? Have molds grown upon the bread?

[Illustration: From Household Bacteriology, by Buchanan. FIGURE 88.—SOME
SPECIES OF MOLDS.]

EXPERIMENT 81: EFFECT OF MOISTURE AND LIGHT UPON THE GROWTH OF MOLDS.— Sprinkle a thick piece of bread with water, place it on a saucer, and cover with a jelly glass or any glass dish. Leave in a light place at room temperature for several days. Examine. Is the bread moist or dry? Have molds grown upon the bread?

From the results of Experiments 80 and 81 what would you say has caused the molds to grow? What conclusion can you draw

from this concerning the growth of molds upon foods in damp and dry places and in damp and dry weather? How should bread be stored in dry weather? In damp weather? Give the reason for storing Dried Bread Crumbs as directed in Lesson L.

EXPERIMENT 82: EFFECT OF MOISTURE AND DARKNESS UPON THE GROWTH OF MOLDS.— Repeat Experiment 81, except the method of covering. Cover with an earthen dish so that the light is excluded. Let it remain at room temperature for the same length of time as given in Experiment 81. Have molds grown? How does the growth compare in quantity with that of Experiment 81?

EXPERIMENT 83: EFFECT OF MOISTURE AND LOW TEMPERATURES UPON THE GROWTH OF MOLDS.—Repeat Experiment 81, but place the bread on the lower shelf of the refrigerator. After several days, examine. Have molds grown? How do they compare in quantity with that of Experiment 81? What conclusion can you draw from this concerning the temperature at which food liable to mold should be kept?

EXPERIMENT 84: GROWTH OF MOLDS UPON CUT FRUIT.—Place pieces of apple, banana, lemon, or other fruits on separate saucers and cover each with a glass dish. Place some lemon or other fruit juice in a test tube and allow it to stand. After two days examine. Have molds grown on all the fruits? Do you notice any difference in the quantity of the molds on the different fruits? Have molds grown on the fruit juice?

EXPERIMENT 85: GROWTH OF MOLDS UPON WHOLE FRUITS.—Place whole fruits, such as apples and lemons, on saucers and cover with glass. After two days examine. Have molds grown upon the whole fruits? If so, how do the molds compare in quantity to those growing on cut fruit? Account for this difference. Apply the results of Experiments 84 and 85 to the "keeping" of fresh fruits.

EXPERIMENT 86: GROWTH OF MOLDS ON OTHER FOODS.—Place a piece of cheese and a piece of meat on separate saucers and cover each with a glass dish. After two days examine. Have molds grown upon these foods? Account for the growth of molds upon these foods when no moisture was added to them. Devise a method for keeping cheese free from mold. Give the reasons for your method.

EXPERIMENT 87: GROWTH OF MOLD UPON WOOD.—Soak a bit of wood in water for at least 15 minutes. Cover it with an earthen dish and let it stand at room temperature for several days. Examine. Have molds grown upon the wood? What has caused the molds to grow upon the wood? From this give directions for the care of the wooden part of the dasher of an ice cream freezer. Draw conclusions concerning the care of pastry and bread boards and butter paddles after scrubbing. Draw conclusions concerning the scrubbing, drying, and airing of wooden floors.

EXPERIMENT 88: GROWTH OF MOLDS UPON CLOTH.—Sprinkle a bit of cloth with water. Cover with an earthen dish. Let stand a few days at room temperature. Examine. Have molds (mildew) grown upon the cloth? What caused the molds to grow? From this draw a conclusion concerning the care of washed clothes, wet dish-cloths, towels, and wash-cloths.

EXPERIMENT 89: CONTAMINATION OF FRESH FOOD BY MEANS OF MOLDY FOOD.—Dip a piece of bread in water and place it on a saucer. With a knitting needle, place bits of mold at several points on the surface of the bread. Cover with a glass dish. After several days examine. At what points on the bread have the molds started to grow? What conclusion can you draw from this concerning the placing of moldy food with fresh food? When fruit is falling to the ground, tell how an orchard should be cared for. Explain.

The following experiments show the growth of bacteria on food:

EXPERIMENT 90: GROWTH OF BACTERIA.—Into test tubes put one of the following foods: (1) bit of uncooked meat; (2) small quantity of egg; (3) piece of bread; (4) crushed peas or beans; (5) sugar or syrup. Add a little water to each tube. Set aside in a warm place. After several days, examine. What change in appearance do you note? What has caused the foods to spoil?

EXPERIMENT 91: EFFECT OF BOILING ON THE GROWTH OF BACTERIA.—Place a little chopped meat in two test tubes. Add lukewarm water to each. Boil the contents of one of the tubes for several minutes. Set both aside. After 24 hours, examine. What difference is there in the condition of the meat in each tube? Explain this difference. From the result of this Experiment draw conclusions regarding the boiling of food to prevent spoiling.

EXPERIMENT 92: EFFECT OF PRESERVATIVES ON THE GROWTH OF BACTERIA.—Beat slightly an egg white. Add to it 1/2 cupful of water. Pour a little of the diluted egg white into four test tubes. To three of the test tubes add one of the following: (1) salt; (2) sugar; (3) vinegar. Put all of the tubes in a warm place. After several days, examine. What is the condition of the egg white in each tube? Explain. Draw inferences regarding the use of "safe" preservatives to prevent foods from spoiling.

THE PRINCIPLES OF PRESERVING FOOD.—Food may be preserved by opposing the growth of microorganisms or by destroying them. Low temperatures, certain preservatives, and drying destroy microorganisms or retard their growth.

[Illustration: From Household Bacteriology, by Buchanan

FIGURE 89.-THE FOUR TYPES OF BACTERIA. A, cocci; B, bacilli; C, spirilla;
D, branched filamentous organism.]

Drying is effective in preserving such foods as fruits, certain vegetables, fish, and meats. The drying of fruit and vegetables may be done in the home. This process of food preservation is often advisable when there is an excessive supply of fruit or vegetables in the orchard or garden.

Substances known as preservatives are used in food preservation. Some of these are harmless, as sugar, salt, vinegar, and spices. Others are harmful, as formaldehyde, boric, salicylic, benzoic, and sulphurous acids, with their related compounds. Saltpeter and smoke are also preservatives. There is some doubt concerning the harmlessness of these latter preserving agents. Foods preserved with harmful materials should never be used. Good food materials can be preserved without the use of harmful preservatives.

The destruction of microorganisms by heat is the basic principle of preserving much food, especially fruit and vegetables. In order to preserve fruits it is necessary to process them, i.e. to apply heat in such a way as to insure preservation and secure the maximum of good quality. To do this, the fruit must be cooked well, packed in cans which have been boiled, and sealed to exclude the air from them. It is necessary, also, to sterilize all utensils which come in contact with the foods in the processes of cooking and sealing.

If canned fruits do not "keep," some microorganisms either in the fruit, on the can, or on the utensils used in canning, have not been destroyed, or the can has not been securely sealed. Slight flaws in the can or rubbers which were not detected at the time of sealing may cause the spoiling of carefully canned fruit. In the preservation of fruit, every effort should be made to secure sound fruit, perfect jars, and good rubbers, and to have the fruit and utensils perfectly processed, and the jars securely sealed. Failure to accomplish these ends may result in much loss of materials and time.

KINDS OF SPOILAGE.—As mentioned previously, canned foods spoil either from imperfect processing or sealing. Different organisms growing in preserved foods cause different kinds of spoilage. A discussion [Footnote 123: Adapted from Journal of Home Economics, Vol. X (July, 1918), pp. 329- 331, "A Consideration of the Canning Problem," by Elizabeth F. Genung.] of the various kinds of spoilage follows:

(a) FERMENTATION OR "SWELL."—When canned foods spoil with a production of gas, fermentation of the food is taking place. The visible indications of such spoilage are gas bubbles in the jar and a bulging of the lid of a jar or a distending of the top and bottom of a can. Because of the latter condition, the term "swell" is used in the commercial canning industry to designate this kind of spoilage. When fermentation takes place, the lid of a jar may become loosened instead of bulged.

This type of spoilage is caused by the action either of yeast or of a certain kind of bacterium which thrives best without air. It is usually due to imperfect sterilization. Fermentation can usually be detected by the presence of bubbles of gas in the jar and a loosening of the sealed cover.

(b) Flat Sour is a kind of spoilage in which no gas is formed, but acid is produced, giving the food a sour taste. In some cases of flat sour, a milky deposit appears in the bottom of the jar which can be detected if the container is glass. In other cases, no change in the appearance of the jar and its contents takes place.

Little is known of the kind of organism producing flat sour. Whether or not food thus spoiled is injurious also has not been determined.

Flat sour is probably due to imperfect sterilization.

(c) PUTREFACTION.—When putrefaction takes place, food decays and disintegrates, or decay takes place with the production of a gas of a disagreeable odor. This type of spoilage is readily detected. Food thus affected is unfit for use.

Putrefaction is usually caused by imperfect sealing. It may result, however, from imperfect sterilization.

(d) BOTULISM.—A bacillus termed botulinus sometimes grows on canned foods, especially those rich in protein or lacking in acid. This organism produces a violent poison in the food. But fortunately, the poison may be destroyed by boiling the food for ten minutes. Hence, it is advisable to boil canned food at least 30 minutes before using. This should be done even though the food is to be served cold. It may easily be cooled after boiling. When there is the least suspicion that food is spoiled, it should be discarded.

QUESTIONS

Explain why boiled milk keeps sweet for a longer time than uncooked milk.
Why do foods need to be sealed to preserve them?

Why does cooked meat "keep" longer than uncooked meat?