Proper Canning Techniques

It won't be long before we will be enjoying one of summer's greatest pleasures, homegrown vegetables and fruits. Home food preservation is still done by many and is a very rewarding activity. However, there are food safety precautions that must be observed during these processes. Today, we will talk about canning basics.

Canning does two things. Foods are heated for specified times to kill the ever-present molds, yeasts, and bacteria that cause food spoilage. Heating also destroys food enzymes that continue the ripening process, eventually resulting in spoilage.

Processing means heating at a specified temperature for a specified time. The temperature is either a boiling-water-bath temperature (212°), or temperatures reached in a pressure canner such as 10 pounds pressure (240°). Processing times and temperatures vary. They are based on the food, jar size, and type of preparation.

Why do some foods take longer to process? Why can some be processed at boiling-water temperatures while others must be heated under pressure to higher temperatures?

For example, apple juice is processed for a shorter time than the thicker product, applesauce. Green beans need a higher processing temperature than tomatoes. And okra takes longer to process than green beans although both are processed at the same temperature.

The temperature at which a food is canned is determined by the amount of acid in the food. In canning, foods are divided into two groups:

1. High Acid and

2. Low Acid.

High acid foods contain more natural acids. Generally, tomatoes and all fruits except figs are high acid foods. The presence of these natural acids helps prevent growth of some spoilage microorganisms. However, consumers have demanded more low acid table tomatoes, and we recommend adding lemon juice, vinegar, or citric acid to all canned tomato products. This is a prevention method for the deadly Clostridium botulinum bacteria.

If the food product has a high enough acid level, boiling-water temperatures are high enough to destroy spoilage organisms.

Low acid foods, such as vegetables and meat products, contain very little natural acid. They must be processed at higher than boiling-water temperatures to destroy any Clostridium botulinum bacteria. Water boils at 212 degrees F, at sea level, and at a lower temperature at higher elevations. Turning up the temperature under the pot or letting the water boil for a long time does not raise the temperature of the water above its boiling point. To make water boil at a higher temperature, it has to be put under pressure, such as in a pressure canner.

When a food is processed at 10 pounds pressure, the water boils when it gets to 240°, rather than at 212°. This is high enough to kill the bacteria that causes botulism poisoning.

Pressure canners must be used to process vegetables, meats, poultry, seafood and soups. Mixed foods that contain both high and low acid foods, are not recommended, but if done, must be processed using the time for the vegetable with the longest pressure canning processing time.

Every year I get a comment from someone who says they have always canned their green beans in a water bath canner, or that their grandmother always did it that way and no one ever got botulism. And thank goodness! The next batch may have been the one with the deadly toxin. Perhaps a safer canning method was not available to Grandmother, but we benefit from research and technology now and there is no excuse for taking this risk.

Botulism bacteria are present in soil and water and are found naturally on the surface of fresh foods. Washing removes some of them. So does peeling, shelling, and other preparation steps. However, the final "killer" of botulism bacteria is heating food using the proper method and time. This means boiling-water-bath canning for acid foods and pressure canning for low acid foods.

Botulism bacteria grow in the absence of air, such as in a vacuum-sealed canned food. If the botulism bacteria haven't been destroyed by proper heating, a sealed jar is a perfect place for them to grow and produce the deadly toxin.

Canning books contain the precaution: BOIL ALL HOME CANNED VEGETABLES BEFORE TASTING...10 minutes for most vegetables, 20 minutes for corn, spinach and greens. This refers to properly processed vegetables. It doesn't mean you may water-bath-process your green beans and then boil them to make them OK.

Grandmother was lucky. She got past all the IF'S involved in getting botulism, and you are here to read this article. But there is no reason to take a risk today when proper pressure canning gives you a safe product.

Continue to next week's article

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