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Home and Farm Food Preservation
Chapter IV - Canning Vegetables


As a rule, vegetables are more difficult to can successfully than are fruits. However, if the fundamental principles involved are well understood, good results may be uniformly. obtained in canning all vegetables with ordinary kitchen equipment. The difficulties of vegetable canning and methods of overcoming these difficulties are taken up in the following paragraphs.

A great deal of interest has been taken recently in vegetable canning, because of cases of fatal poisoning from the use of home canned vegetables. These poisonings have been caused by a very powerful toxin produced in jars or cans of improperly sterilized vegetables by the growth of an organism known as Bacillus botulinus. Experiments and experience have shown, however, that the methods described in this book are perfectly safe. All that is necessary is that the methods be well understood and applied intelligently.

16. Peeling and Preparing. Vegetables for canning should be as fresh as possible. Waste no time in getting the vegetable from the garden into the can. Asparagus becomes tough and bitter if held twenty-four hours. String beans lose flavor and crispness; peas may ferment; and corn loses in flavor and sweetness if kept too long uncanned after gathering. The vegetables should therefore be canned on the same day that they are picked.

Vegetables should usually be graded for size and appearance. The amount of grading will depend on whether the product is for home use or for sale. Grade asparagus into two or three sizes and peas into young tender pods and larger, more mature pods. Other vegetables need not be graded, unless for sale. In this case select the material of best appearance for canning for market and the less attractive vegetables for home use.

The vegetables should be thoroughly washed to remove earth, etc. A large tub may be used for this.

In small scale canning the peeling, cutting, and preparation for the can must in practically all cases be done by hand. Root vegetables such as beets, turnips, and carrots, may be peeled by the peeler shown in figure 43. In canning factories, peas are threshed and graded by machinery, while corn is silked and cut from the cob by special machines. Other vegetables are prepared largely by hand labor.

17. Blanching or Parboiling. Most vegetables are given a short preliminary boiling in water after grading, cutting, and peeling. This improves the texture and color and usually removes disagreeable flavors and mucilaginous substances from the skins. The process is spoken of as "blanching," but is nothing more nor less than parboiling.

The prepared vegetables are placed in a screen basket or in a cheesecloth and plunged into vigorously boiling water for a length of time varying from a few seconds to ten minutes, the time depending on the vegetable and its degree of maturity. Small green peas will require less than a minute, while large stalks of asparagus may require ten minutes' blanching. Blanching cooks the vegetables more rapidly than cooking in the can, and tough vegetables can be made tender with less trouble in the blanching process than in the sterilization process. Convenient methods of blanching are illustrated in Fig. 8. Tomatoes are parboiled or steamed about one minute and beets about fifteen minutes to cause the skins to slip off easily in peeling. They are chilled after heating to facilitate handling in peeling.

18. Chilling. The blanched vegetables must be placed in the can with all expediency. To make them cool enough to handle, they should be plunged into cold water after blanching. Chilling in this way also sets the color in green vegetables and tends to make most vegetables more crisp.

19. Brine and Acidified Brines. Vegetables, with the exception of tomatoes, are canned in dilute brine. Tomatoes are canned without any liquid except their own juice.

The usual brine contains from two to three ounces of salt per gallon. For practical purposes, an ounce is equivalent to a level tablespoonful of salt; this rule will save trouble in making up small quantities of brine.

Most vegetables are deficient in acid and if canned in a salt brine only are very difficult to sterilize. That is to say, the spores of the bacteria occurring on vegetables are very difficult to kill under this condition. If, however, the deficiency in acidity of the vegetables is made up by the addition of a small amount of some harmless acid substance such as lemon juice or vinegar, the vegetables are as easily sterilized as fruits. For example, in ordinary brine, asparagus must be sterilized for at least three hours in boiling water, while if a small amount (4 ounces or 8 tablespoonfuls per gallon) of lemon juice is added, this vegetable may be sterilized in one hour or less. Other vegetables behave similarly. Vinegar may be used to replace lemon juice, although slightly 'more is needed because ordinary vinegar is not quite so acid as lemon juice. The following table gives the amounts of salt and lemon juice or cider vinegar to use for various vegetables.

The advantage of this so-called "lemon juice" method is that the time of sterilization in water at 212 is greatly shortened and made much more certain. It is probably the most satisfactory method for home canning. The amount used does not materially affect the flavor. The brine can be discarded when cans are opened and the vegetables cooked in fresh liquid or a small amount of baking soda may be added.. This will remove practically all taste of the lemon juice or vinegar, should this flavor prove objectionable. Many vegetables are improved by the addition of the small amount of lemon juice or vinegar recommended.

20. Addition of the Brine. The brine should be added boiling hot to cans that are to be sealed, or the cans should be exhausted in steam or boiling water before sealing (see paragraph 14). Jars require a shorter time to heat if filled with hot brine. A teapot makes a very convenient utensil for heating and pouring brines or sirups into cans or jars. (See Fig. 10.)

21. Sterilization. Four ways of sterilizing vegetables are used. These are: (a) Sterilization under steam pressure; (b) intermittent sterilization in boiling water; (c) sterilization in boiling water by a single long sterilization; and (d) sterilization in boiling water by a relatively short heating after addition of a small amount of lemon juice or vinegar to the brine used in canning.

(a) Pressure Sterilization: The boiling point of water rises if steam is confined in a closed space, and temperatures much above 212 F. can be attained in this way. By this means the spores of many bacteria that are killed with the greatest difficulty at the temperature of boiling water are destroyed by a few minutes' heating under five to fifteen pounds' steam pressure. These pressures correspond to 228 F. and 250 F., respectively.

The following table shows the relation between steam pressure in pounds per square inch and temperature in degrees Fahrenheit. The table is of use where the sterilizer used may not be equipped both with a thermometer and a steam gauge.

The steam pressure sterilizer is independent of altitude and therefore is of value in elevated regions.

Several forms of steam pressure sterilizers for home use are on the market. There is one known as the "water seal outfit," which gives temperatures only slightly above the boiling point of water. This is considered favorably by many home canners; because it requires only a small amount of water, is easily heated, and is inexpensive. Another type can be operated only up to five pounds' pressure per square inch. Most forms of pressure cookers will withstand a steam pressure of 15 pounds or more per square inch.

Steam pressure sterilizers or retorts can be obtained in sizes holding from two dozen cans to several thousand. The small outfits are heated by direct heat; the large ones, by steam from a boiler.

Steam pressure sterilizers can be used for sterilization at 212 F. by simply opening the release cock and keeping the pressure at 0 pounds.

Steam pressure sterilizers are well suited to sterilization of cans but are not convenient for jars.

In using the sterilizer, seal the cans of vegetables hot and place them in the basket or crate. Add water to the depth of several inches. Lower the crate and contents into the retort. Clamp the lid securely on the sterilizer and leave the release cock open. Heat the water to boiling and as soon as steam escapes freely from the cock close it. The purpose of leaving the cock open at first is to allow the steam to displace the air in the retort; otherwise the pressure in the retort would be due to compressed air and the temperature would be uneven and not in proportion to the indicated temperature or pressure. Heat until the dial of the steam gauge indicates the desired pressure or until the thermometer reaches the desired temperature for the required length of time by regulating the fire or by opening the release cock sufficiently, and by setting the weight on the safety valve so that it will release the steam automatically when the proper pressure is reached.

When the cans have been sterilized sufficiently, open the release cock and as soon as the pressure falls to zero, remove crate and contents and cool in a tub of cold water if cans have been used.

If jars are used, leave the lids and rubbers on loosely during sterilization. Close immediately after removal from the sterilizer, but do not, of course, chill the jars. (See Fig. 18.)

(b) Intermittent or Three-Day Sterilization of Vegetables at 212 F. is accomplished by heating the container and contents to the boiling point of water for a specified length of time on several (usually three), consecutive days. It is the most effective method at 212 F., because the bacterial spores start to grow between sterilizations from the softening effect of the heat and are easily killed by the second and third sterilizations.

Cans are sealed hot and heated usually for one hour in boiling water or steam on each of three successive days. Jars are heated the first day with rubbers removed and caps on jars loosely. At the end of the first sterilization rubbers are sterilized in boiling water about five minutes, placed on the hot jars and the caps are screwed down. The second and third days the sterilizations are carried out without loosening the caps because the vacuum formed after the first day's sterilization will prevent bursting of the jars.

The three-day method is safe, but often softens the vegetables so much that they become unattractive in appearance.

(c) Sterilization of Vegetables at 212 F. by One-Period Method: By this method the vegetables are heated in boiling water or steam once only, but for a long period of time. The method is recommended strongly by the United States Department of Agriculture in Farmers' Bulletin 839 and is in extensive use.
No pressure sterilizer is used with this method. It sometimes results in softening of the vegetables from overcooking. Results of investigations by Dr. Dickson of Stanford indicate that this method does not always kill spores of certain bacteria. Method "(2)," described below, requires a shorter time of sterilization and therefore results in a more attractive product.

(d) Sterilization by the Lemon Juice Method: If a small amount of harmless vegetable acid in the form of lemon juice or vinegar is added, the brine vegetables are, easily sterilized by a single sterilization at 212 F. The vegetables are best acidified by adding the lemon juice or vinegar to the brine used in filling the cans or jars. The amounts to use for various vegetables will be found in Table 4. The method is used as follows:

Pack the vegetables in the usual way. Add the hot brine which has been acidified. Seal the cans and put rubbers and caps loosely on the jars. Sterilize in boiling water or steam from three-quarters to two hours, depending upon the vegetable. Remove cans and chill in water. Remove jars and seal.

This method does not result in overcooking and retains the color and flavor more perfectly than other methods. It produces a slight acid taste in some vegetables. This can be removed before cooking for the table by drawing off the brine and cooking in fresh water in the usual way or by adding a small amount of baking soda before cooking for the table. The method has been proven safe and free from danger of botulinus poisoning.


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