In open kettle canning, food is cooked in an ordinary kettle, then packed into hot jars and sealed with processing. The temperatures obtained in open kettle canning are not high enough to destroy all spoilage and food poisoning organisms that may be in the food. Also, microorganisms can enter the food when it is transferred from the kettle to jar and cause spoilage. Properly canned food stored in a cool, dry place will retain optimum eating quality for one year. This can be dangerous because the temperature will vary according to the accuracy of oven regulators and circulation of heat.
Jars explode easily in the oven.
A. Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit on the underside of jar lids. This deposit on lids of sealed, properly processed canned foods is harmless. A. Liquid did not cover food or food was not processed long enough to destroy enzymes. A. Loss of liquid may be due to the fluctuating pressure in the pressure canner, food packed too tightly in jars or lowering pressure too suddenly. At the end of processing time, allow the pressure to drop to zero naturally and wait two to five minutes before opening the lid.