MICROORGANISMS IN THE SPORE FORM.—Many microorganisms are destroyed by heating them for a few minutes to boiling temperature. However, some microorganisms have a peculiar power of retaining life under most adverse conditions. When subjected to extreme heat or cold, intense drying, or when there is lack of food, certain microorganisms assume a spore form, i.e. they cease growing and reproducing, and are able to undergo conditions which would readily kill microorganisms in the active form. Some microorganisms in the spore form are able to resist the temperature of boiling water for an hour or longer. Then as soon as the adverse conditions mentioned above are removed, the microorganisms assume active form and begin to grow and reproduce. In the growing state, their destruction is not so difficult.

Some of the microorganisms in certain foods, especially vegetables and fruits grown in a dry season, are capable of spore formation. When microorganisms in spore form do exist in foods that are to be canned, or the microorganisms change into spore form during the canning process, the microorganisms may not be destroyed by the time the ordinary process of canning is completed. If such is the case, when the canned foods are cooled and the conditions are favorable for growth, the microorganisms assume active form, begin to grow, and cause the decomposition of food. Twenty-four hours is sufficient time for the microorganisms to change from the spore to the active form. Hence the canned foods must be heated again, if they are to be preserved. For foods difficult to process (for the reason given above) processing should be carried on for three successive days. This is called intermittent processing.

Destruction of microorganisms in the spore form can be accomplished in a short time by subjecting them to very intense heat. In canning factories this is done by processing at a temperature higher than that of boiling water. In the home this may be accomplished by processing in the pressure cooker. According to one authority processing intermittently, i.e. on three successive days, does not insure satisfactory processing of materials containing spores.

SINGLE PERIOD AND INTERMITTENT PROCESSING.—The acid of tomatoes and fruits aids in the destruction of microorganisms. Hence intermittent processing is unnecessary for these. Processing tomatoes and fruits in a hot water bath for one period has proved very satisfactory and certain.

There is some question, however, regarding the safety of canning all vegetables by one period of processing in the water bath at 212 degrees F., especially in regions where botulism is known to occur and where Foods cannot be stored in a cool place. In Farmers' Bulletin 1211, "Home Canning of Fruits and Vegetables," revised August, 1922, one period of processing in the water bath at 212 degrees F. is not advised in climates where the storage conditions are trying for the following vegetables: corn, beans, asparagus, okra, spinach and other greens, and peas (especially if at all mature). For processing these vegetables, a higher temperature than that obtained in the boiling water bath is recommended. Processing at a high temperature (from 228 degrees F. to 250 degrees F.) can be accomplished conveniently by means of a pressure cooker. This is especially recommended for vegetable canning in high altitudes and in localities where botulism has occurred.

It is thought that in some places the above mentioned vegetables may be processed intermittently with safety. For vegetables difficult to can, pint jars only are recommended for both intermittent and single period processing in the water bath. Heat penetrates more rapidly to the center of the small jars than to the center of the large jars.

SELECTION AND PREPARATION OF VEGETABLES AND CANNING.—Young vegetables, especially those that have grown quickly, are most desirable for canning. If possible, vegetables, especially corn, should be canned immediately after picking.

Vegetables for canning should be thoroughly washed, pared, scraped, or cut into pieces in the same manner as when they are cooked and served immediately. If the vegetables vary in size, it is well to sort them and fill jars with those of uniform size. If there is much difference in ripeness, sort the mature and young vegetables.

METHOD OF CANNING VEGETABLES.—The method of canning vegetables for a single period does not differ greatly from the method of canning fruits. The chief difference is that jars containing fruit are filled with sirup, while those holding vegetables are filled with water and salt is added. Blanch and cold-dip vegetables as directed previously, for the length of time given. Greens and vegetables of delicate flavor are blanched most successfully by steaming either in a colander placed over boiling water or in a steamer. (Steaming greens prevents the escape of volatile oils and other materials.) Pack the vegetables in jars to within 1/2 inch of the top. It is well not to pack spinach and other greens too solidly in jars. Since lima beans, corn, and peas swell during processing, they should be packed only to about 1 inch of the top of the jar. To each jar add salt,—1 teaspoonful to each quart jar. Fill each jar to 1/2 inch of the top with boiling water. Put a new rubber on the jar, partly seal the cover, and proceed as directed for fruit (see Table below for the length of time for processing).

When vegetables are processed intermittently, jars with glass tops and spring clamps are recommended. In processing vegetables for three successive periods, the same method of processing and sealing is followed as for the single period. At the beginning of the second and third periods, raise the clamps of the jars to allow for expansion, then fasten the clamps at the close of processing period (see Table for the length of time of processing on each of the three successive days).

FOOD PRESERVATION

TABLE FOR CANNING FRESH, SOUND, AND FIRM VEGETABLES BY ONE PERIOD OF
PROCESSING [Footnote 131: Adapted from Farmers' Bulletin 1211. Revised
August, 1922.]

TIME OF PROCESSING
TIME OF
VEGETABLE BLANCHING OR (a) (b) Steam Pressure
Water (Pressure Cooker)
COOKING Bath at (1) 5lb (2) 10lb (3) 15lb
212 deg. F. 228 deg. F. 240 deg. F. 250 deg. F.
Minutes Hours Minutes Minutes Minutes
Asparagus 4 - - 30 to 40
Corn 1 to 5 - - 90 60 to 90
Lima beans 3 to 5 - - 45 to 60
Okra 6 to 8 - - 30
Peas 3 to 8 - - 40 to 50
Spinach 4 in water or
15 in steam - - 90 35
String beans. 3 to 5 - - 40 to 50
Tomatoes 1 to 1 1/2 to
loosen skins 1/2 15 10

[Footnote for Asparagus: Scrape off tough outer skin of asparagus. Tie into bundles for blanching. Blanch tough ends 2 minutes and entire bundle 2 minutes longer.]

[Footnote for Corn: Blanch corn on the cob, then cold dip and cut from the cob. For each pint jar, use 1 pint of cut corn, 1 cupful boiling water, and 1/2 tea-spoonful each of salt and sugar. Cook the mixture in a saucepan until it boils and pour immediately into a hot, sterilized jar.]

[Footnote for Okra: Cold dip okra in salt water (1 tablespoonful salt to 1 quart water).]

[Footnote for Spinach: To loosen grit, cover spinach with scalding water, let stand 1 or 2 minutes. Then wash in several cold waters. Do not cold dip after blanching.]

[Footnote for Tomatoes: Pack tomatoes whole in jars, then fill the jars with cooked and strained tomato pulp. Tomatoes cut into pieces may be packed closely in jars. When this is done, no liquid need be added.]

NOTE.—Processing in the hot water bath is not advised for non-acid vegetables such as asparagus, corn, lima beans, okra, peas, spinach, and string beans.

Count time of processing in a water bath after the water boils.

When two different times of processing are given, use the longer time for quart glass jars, the shorter time for tin cans.

If the jar is packed tightly, increase the time of processing.

For altitudes higher than 1000 feet, increase the time of processing 10 per cent for each additional 1000 feet. For very high altitudes, the pressure cooker rather than the hot water bath should be used.

TIME TABLE FOR CANNING VEGETABLES BY INTERMITTENT PROCESSING [Footnote 132: See statements previously]

VEGETABLE TIME OF TIME OF PROCESSING IN WATER BATH
BLANCHING AT 212 F. 12 TO 18 HOUR
INTERVALS BETWEEN PERIODS
(a) First Day (b) Second
and Third Day

Asparagus 10 to 15 60 60
Corn 5 to 10 90 90
Lima Beans 3 to 5 90 90
Peas 5 90 90
String Beans 3 to 5 90 90

[Footnote 133: (For Asparagus, Corn, and Lima Beans) Process in pint jars only. See footnotes for Asparagus and Okra, above.]

USE OF CANNED VEGETABLES.—Open the can and if it is tin, empty its contents at once. If the vegetable is surrounded by liquid, use the water in cooking the vegetable, as it contains valuable materials. There are some who contend, however, that the flavor of certain vegetables such as peas and string beans is improved if the vegetable water is drained from them and they are cooked in fresh water. If this is done, the vegetable water should not be wasted. It should be used in making soup or sauce. If possible, let the vegetable stand exposed to the air for an hour or longer.

If the vegetable is to be served plain, turn into a saucepan. Cook in its own liquor at boiling temperature, for at least 30 minutes. (Cooking at boiling temperature for this length of time is advised to remove any possible danger of botulism.) When cooked, the liquid should be almost entirely evaporated. Add butter, salt, and, if desired, a very little sugar, and serve hot.

A White Sauce may also be used with a vegetable that has been heated as above.

QUESTIONS

Explain why vegetables (except tomatoes) are more difficult to can successfully than fruits.

What foodstuffs does the water in which vegetables are canned contain? From this explain why the water should not be drained from vegetables when removing them from the cans.

What is the purpose of cooking canned vegetables at boiling temperature?