DO-IT-YOURSELF : Better Can the Shortcuts When Preserving

It’s a comforting and satisfying reminder of a slower, simpler time: shelves lined with rows of Mason jars gleaming with brightly colored preserved fruits and vegetables. For many, home canning and preserving remain an enjoyable way to keep a bit of summer and early fall in the larder throughout the months when ripe peaches, strawberries, blueberries and tomatoes are only a memory.

But those who love to put up preserves must also put up with a series of the most stringent and inflexible of all rules of cooking. Because ignoring them, or even taking culinary shortcuts, can be fatal.

The villain is a tiny heat-resistant spore that lives naturally in soil and can produce bacteria that may contaminate the fresh foods to be canned. Its Latin name is Clostridium botulinum, and it can produce a poison that is the most deadly bacterial toxin known: the botulinus toxin that causes botulism.

Proper cooking and canning methods, however, absolutely ensure that any spores that may have gotten into the food will be killed, broken down and rendered harmless. But aspiring home canners must become fledgling chemists and realize that they are dealing with a kind of biological Catch-22: the very condition--an airtight sealed container--that allows you to eat canned summer squash in February also creates one component of the ideal environment for the growth of the botulinum toxin.

Botulinum is anaerobic, which means that it can produce toxin in an environment without oxygen. This process can be counteracted, however, by a handful of elements and processes. For instance, it is less likely to be present in foods that are high in acidity, such as tomatoes or citrus fruits.

The Ph, or acidity, of the food generally must be greater than 4.6 for the toxin to grow, said Kathy Karlheim, a pharmacist and the assistant director of the Orange County Regional Poison Center.

Sugar, too, helps to counteract the development of the bacteria. “If something’s preserved in sugar, you probably don’t have to worry about it,” said Bob Merryman, the director of the environmental health division of the Orange County Health Care Agency.

The other two weapons in fighting botulinum are pressure and heat, Karlheim said. Foods to be canned must be cooked in a pressure cooker at a temperature of at least 250 degrees Fahrenheit for no less than three minutes. They must then be boiled at 212 degrees Fahrenheit for at least one minute or heated on the stove at 170 degrees for at least 20 minutes.

Finally, the container in which the food is kept should be sterile and must have a seal tight enough not to allow even a single botulinum spore to enter from the outside environment, Merryman said.

If for some reason the seal is broken, there can be a visual giveaway, he said. Most canning jar lids are concave. If that lid has been pierced, or if it appears to be bulging out rather than in, spores may be germinating inside, and the contents should be thrown away down the garbage disposal.

A leaking container, Merryman said, should be considered just as dangerous, and should be handled in the same way.

A “slight off taste” also can be an indication that botulinum is present, said Merryman, who recalled the case of a Riverside man who spit out one of his wife’s home-canned green beans after noting an odd taste. Botulinum was present and, Merryman said, the man might have died had he eaten an entire mouthful.

The growth of botulinum toxin is extremely rare in commercially canned products, Merryman said, but any swollen or leaking cans still should be removed from the pantry and their contents disposed of down the kitchen drain.

Also, Merryman said, a commercial can should be avoided if it is dented on one of its seams, which may cause a break in the seal. Cans dented on their sides, however, likely are safe.

Botulism also is rare. The small number of cases seen are almost always from poor technique in home canning, Karlheim said. The effects, however, can be dramatic.

The botulinum poison, Karlheim said, is a neurotoxin, attacking and disabling the body’s nervous system in a “top-to-bottom” set of symptoms. Headache, dizziness and blurred vision are common in the early stages and are often followed by a dry and constricted throat and difficulty in swallowing and speaking.

As the nerve paralysis extends to the chest area, there is a danger of a loss of function of the respiratory muscles, which prevents the victim from breathing. This accounts for about half the deaths from botulism.

Merryman emphasized, however, that such trouble is easily avoidable by simply “following the recipe,” albeit to the letter.

Description of proper canning techniques is available in several cookbooks. The classic “The Joy of Cooking” offers a particularly thorough and detailed set of instructions--along with a welcome reminder of the pleasure to the eye and the palate that a successful home canning session can produce.