METHODS OF CANNING
Canning is a method of preserving and storing food. Sealing food in containers and processing it at boiling or above boiling temperatures destroys the molds, yeasts, bacteria, and enzymes that are in or on the food. In canning, heating destroys microorganisms that can make the food unsafe to eat, as well as change its flavor, color, and texture; sealing keeps new ones from getting to the food.
A Frenchman named Nicholas Appert is credited with the discovery of canning when he sealed and heated food in glass bottles to help Napoleon feed his troops. For this ingenious work, Appert won a prize of 12,000 francs, as well as the gratitude of generations to follow.
Since Appert first started his experiments, two distinct types of canning have been developed: heating, or processing, in boiling water; and processing under steam pressure. These two methods are used for different types of foods, and are not interchangeable.
The acidity of a food is what determines how it should be canned, because acidity determines what microorganisms can spoil the food.
Food spoilage is caused by molds, yeast, enzymes, and bacteria.
Bacteria are the most difficult to destroy because some of them may thrive at temperatures that kill molds, yeast, and enzymes. Heating food to boiling, sealing it in jars, and then processing it in boiling water will destroy molds, yeast, and enzymes, but not all bacteria. That's where steam pressure canning comes in. The spores of the bacteria are not destroyed until the temperature of the food reaches 240 degrees F. Since water boils at only 212 degrees F, any food that will support the botulism bacteria spores must be processed in a steam pressure canner, where the pressure creates temperatures above boiling.
Although you'll find it easy to can most vegetables successfully, there are a few varieties that are better frozen instead. These are broccoli, Brussels sprouts, cabbage, cauliflower, eggplant, parsnips, edible pod peas, pumpkins, rutabagas, and winter squash.
For all practical purposes, the rest of the vegetables with the exception of the high acid foods; tomatoes, fruits, sauerkraut, rhubarb, and foods with vinegar added such as pickles and relishes which are not popular with bacteria and so can be processed by the boiling water bath method, MUST be steam pressure canned. Also requiring steam pressure canning are meat, poultry, seafoods and soups. This method of canning destroys these bacteria and their by-products. Safe canning procedures should never be shortcutted. To make sure your home canned foods are safe, always process low acid foods (all vegetables except tomatoes) in a steam pressure canner, following the instructions specified in each recipe. When you're canning any combination of acid and low acid foods, such as tomatoes and corn, treat the mixture as a low acid food and process in a pressure canner.
Source: Vegetable Gardening Encyclopedia Typos by Dorothy Flatman 1995
Submitted By DOROTHY FLATMAN On 10-04-95
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