DEAR DR. BLONZ: We recently had a close call with botulism and are lucky enough to be able to tell the tale. I have learned about its causes, symptoms and progress but have one unanswered question: How long is it safe to leave covered food in the refrigerator? I tend to cook one day a week, preparing soups and vegetables for later in the week. They are covered and refrigerated until it's time to eat them. Would it make a difference if they were uncovered? What other precautions should we take? Also, what risk is there to our dog from botulism? -- W.O., Albany, N.Y.
DEAR W.O.: First, some background for readers who are not as familiar with botulism as you now are. Botulism is a very severe type of food poisoning -- much worse than the flu or E. coli that we hear of periodically in the news. An amount of botulism toxin the size of a single crystal of salt can kill several people in less than hour.
To appreciate how botulism works, it helps to understand its three facets: the bacteria, its spores and the deadly toxin. The bacteria's name is Clostridium botulinum, it reproduces by giving off spores, and these spores are what produce the deadly toxin. Botulism is caused when an individual has the misfortune of ingesting foods contaminated by the toxin.
The bacteria are found everywhere and are usually present in soil. What is particularly insidious about these bacteria is that the spores can remain in a vegetative state for extended periods until they are either destroyed, or until conditions become right for them to grow.
The botulinum bacteria can grow in low-acid, oxygen-free environments, and they tend to be a particular problem with improperly processed canned foods, such as vegetables, fish and meat. One saving grace is that the toxin is not heat-stable. Food preservation techniques designed to control these bacteria must include a heat treatment. The botulism toxin can be inactivated when exposed to a temperature of 180 degree F for 10 minutes or longer. Eliminating the Clostridium botulinum bacteria entirely takes exposure to 212 degrees F for 10 minutes or longer. The spores are the most heat-tolerant, requiring exposure to 240 degrees F to destroy them.
The botulinum bacteria are also inhibited by an acidic environment, which is why acidic foods such as tomatoes, citrus and pickled foods tend to be safe. The bacteria are also thwarted by nitrite preservatives, which is why sodium nitrite is added to cured meat products.
In your situation, it becomes essential to follow good kitchen hygiene, scrubbing all foods before use and avoiding any cross-contamination with uncooked foods. Prepared foods should be immediately refrigerated (under 38 degrees F) in covered containers and used within three to five days.
Relying on a once-a-week cooking system is pushing it. You might also consider storing the later-in-the-week portion of your vegetables in the freezer, as toxin production from botulinum bacteria is inhibited at freezer temperatures (0 degrees F). As for your dog: Dogs are less at risk due to their more acidic digestive system. This allows them to drink, eat and lick items that are a bit less than sanitary.
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