School and Home Cooking

by Carlotta C. Greer

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.