This section is from the book "Everywoman's Canning Book", by Mary B. Hughes. Also available from Amazon: Everywomans canning book; the A B C of safe home canning and preserving.
Canning of fruits and vegetables by the process known as Cold-Pack1 may, for convenience, be divided into six steps: Preparation of Materials, Blanching, Plunging, Packing, Processing, and Sealing. Each step is important, and a clear understanding of these terms and familiarity with each process are necessary to success, since they are used throughout the book.
1 Cold-Pack Canning was introduced by the Department of Agriculture in 1915, and is the simplest, most up-to-date method of canning fruits and vegetables. It is indorsed throughout the country by canning experts and practical housekeepers who are familiar with it.
No vegetables or fruits which are withered or unsound should be used. If possible, pick materials the morning of the day they are to be canned. Vegetables and fruits lose much of their flavor by standing, and the fresher they are the better will be the results obtained. Grade, especially for ripeness and size, and pick over carefully. Do not can fruit until it is ripe, unless a recipe calls specifically for green fruit. Have plenty of fresh, clean water, to wash grit and dirt from vegetables.
Parboiling is another term for this process commonly used by the housewife. Blanching is necessary to shrink the product, to start the flow of coloring matter, and to eliminate objectionable acids.
Put vegetables (and some fruits) in a cheesecloth sack or wire basket, and plunge into enough fresh boiling water to immerse completely the material to be blanched.
The time for blanching varies with different vegetables and fruits, and vegetables require longer blanching than fruits. It is important to count the time of blanching from the minute the water begins to boil after the product is immersed.
Blanch greens and green vegetables (like spinach, Swiss chard, asparagus, etc.) over live steam, as the volatile oils are lost when blanched in water, and special food value is wasted. A convenient way to blanch over steam is as follows: Take one and a half yards of cheesecloth; make a hammock over a wash boiler with a little boiling water in it. Tie the two ends of the cheesecloth in the handles at the sides of the boiler, put the greens in the suspended cheesecloth, put on the cover of the boiler, and steam the required time.
In canning berries and all soft fruits, blanching is dispensed with.
Have at hand a large bowl of fresh, cold water, preferably with ice in it (ice is not a necessity), and plunge the vegetables or fruits directly from the boiling water into the cold water. Take out immediately. The plunge should not require more than ten seconds. Never plunge more than one set of vegetables or fruits in the same water. In plunging all vegetables, but especially spinach and other greens, care must be taken that the cold plunge affects the inner portion of the product as well as the surface. Plunging is necessary to loosen the skins, to harden the pulp, to set the coloring matter, and to facilitate the packing.
The material is now ready to go into freshly washed jars. For vegetables, add hot water, and salt for seasoning-a teaspoonful to a quart. For fruits, hot syrup or hot water is used. Fill the jar to one-half inch of the top, put on a new rubber which has been scalded, adjust the cover, and put one clamp of the bail in place. If the jar has a screw top, put the cap in position and screw lightly, using thumb and little finger for pressure.
This part of the work is of the greatest importance. After each jar is partially sealed as above, place on a wire rack in the bottom of a wash boiler. Fill the boiler with water until it reaches two or three inches over the top of the jars. Have the water in the boiler about the same temperature as that of the liquid poured over the material in the jars. This will keep the jars from cracking. Put the cover on the boiler and bring the water to a quick boil. Count the time for processing from the minute you hear the water boiling and bubbling actively in the container. Do not let the fire get low and the water stop boiling, for good material is ruined by careless processing.
Immediately after the termination of the processing period, remove the jars from the boiler. A buttonhook makes a very good aid if the jar has a bail. For screw-top jars it is necessary to buy a commercial jar holder. These can be bought for a small sum. Place the hot jars on a table out of a draft, put down second clamp of bail or tighten screw-top cap with full strength, and invert to cool. Watch closely for leaks. If leakage occurs, tighten the bail. It is well to cover the jars, while cooling, with a clean cloth or towel. If a large number of jars are processed at once, do not place them closely together to cool, but separate them on different tables, so they will cool rapidly. Slow cooling of the jars is undesirable, and affects the flavor of the product.
After processing, set the jars aside for a few days before putting away in the preserve closet. To see if the seal is perfect, unfasten both clamps of the bail and lift the jar by the top. If the top comes off easily, the seal is imperfect. Either reprocess the full length of time given in the tables, or, if fermentation has started, throw material away.