Saturday, June 20, 2009

**Canned Butter Warning**

There are many recipes floating around the internet about how to can your own butter. Basically it entails boiling the butter for a length of time (clarifying it), and then putting in hot jars. The hot liquid would seal the jar, and it would solidify after time. I got really excited about this a while ago and did some for my food storage. After going to a class last night about canning, I am throwing away my 12 pints of butter (luckily, that is all I had done).

Growth of the bacterium Clostridium botulinum in canned food may cause botulism—a deadly form of food poisoning. These bacteria exist either as spores or as vegetative cells. The spores, which are comparable to plant seeds, can survive harmlessly in soil and water for many years. When ideal conditions exist for growth, the spores produce vegetative cells which multiply rapidly and may produce a deadly toxin within three to four days of growth in an environment consisting of:

  • a moist, low-acid food,
  • a temperature between 40°F and 120°F, and
  • less than 2 percent oxygen.
As you can see, canned butter meets all of these requirements.

I really enjoy canning, and follow the rules exactly. The problem with canning your own butter, is that the contents never get hot enough for long enough time to kill the potential botulism spores. Botulism spores are resistant to heat -- even from boiling water -- and thrive in a moist, oxygen-free environment. As botulism spores reproduce, they generate one of the most extraordinarily powerful poisons on earth: one teaspoon-worth is sufficient to kill 100,000 people. Improper home canning creates the perfect environment in which to grow the botulism toxin. Also, because food contaminated by botulism may very well look and smell normal, there is often no warning. That is why home canning must be done properly with extreme care. You must follow the tested recipe exactly.

Whether food should be processed in a pressure canner or boiling-water canner to control botulism bacteria depends on the acidity in the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods contain too little acidity to prevent the growth of these bacteria. Acid foods contain enough acidity to block their growth or to destroy them rapidly when heated. The term “pH” is a measure of acidity; the lower its value, the more acidic the food. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar.

Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most products that are mixtures of low-acid and acid foods also have pH values above 4.6 unless their ingredients include enough lemon juice, citric acid, or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalade, and fruit butters.

Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Figs also have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products must be acidified to a pH of 4.6 or lower with lemon juice or citric acid. Properly acidified tomatoes and figs are acid foods and can be safely processed in a boiling-water canner.

Botulinum spores are very hard to destroy at boiling-water temperatures; the higher the canner temperature, the more easily they are destroyed. Therefore, all low-acid foods should be sterilized at temperatures of 240°F to 250°F, attainable with pressure canners operated at 10 to 15 PSIG. (PSIG means pounds per square inch of pressure as measured by a gauge.) In Utah County (approx. 4500 ft) the proper pressure is 13 PSIG. At these temperatures, the time needed to destroy bacteria in low-acid canned foods ranges from 20 to 100 minutes. The exact time depends on the kind of food being canned, the way it is packed into jars, and the size of jars, as well as the altitude where you live..

Currently, BYU and USU are testing methods of safely canning butter. For now, I will do without.

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