There are several different ways of canning and preserving food. Here I will discuss the process involved in them.
Open Kettle Canning:
This is limited to the canning of fruits and vegetables which are highly acidic such as tomatoes, peaches, cherries and plums. Since the temperature reached never exceeds the boiling point (212), non-acid foods cannot be safely canned this way. In this procedure the foods are simply brought to the boiling point, cooked until tender, and then placed in sterile jars, filled to the brim with juice, covered with sterile lids and sealed. One difficulty may be encountered, that is soft foods may break in packing. On the other hand, no further shrinkage will take place after the jars are filled.
Hot Water Bath (Can-cooking):
Any large kettle or pot may be used provided the bottom is fitted with a wooden or metal rack. The filled jars are placed so that they will not touch each other. The container is filled with water to about 1" above the top of the jars. Do not start counting the length of time of processing until the water boils. Follow the time table to ascertain the processing time for individual foods. Remove jars and seal lids. This method is recommended for fruits and acidic vegetables only.
Pressure Cooker (Can-cooking):
Canning in a pressure cooker is the only way in which the contents of the jar or can may be heated to temperatures higher than boiling. It is the only way in which one can be sure of killing certain bacterial spores which are found in nonacid vegetables, such as peas and corn, and in meats. Follow carefully the instructions that came with the cooker.
Oven Canning (Can-cooking):
This procedure is satisfactory for fruits and tomatoes. Place the filled cans on a rack or a pan in the oven and set temperature for 275. Do not start timing until the oven has reached that temperature. Leave 1-2" space in the top of each can to allow for boiling.
Things to remember:
1. Do not use cans which show cracks or chips.
2. Can nothing but sound, fresh foods.
3. Tighten caps immediately upon bringing them from canner.
4. Do not turn the sealed can upside down to test for leakage.
5. Never tighten the lid after the can cools. The seal may be broken.
6. Never set a hot jar on a cold surface, or in a cold draft of air.
7. Be certain to use all precautions mentioned with the pressure cooker.
8. Store in a cool, dark, dry place.