Putting Food By - Janet Greene [3]
Most dangerous of the bacteria is the tough Clostridium botulinum, which deserves a section of its own.
Botulism
The scientific books describe C. botulinum as a “soil-borne, mesophilic, spore-forming, anaerobic bacterium.” Which, translated into everyday language, means that it is present in soil that is carried into our kitchens on raw foods, on implements, on clothing, on our hands—you name it. Next, it thrives best in the middle range of heat—beginning at about room temperature, 70 F/21 C, on up to 110 F/43 C. Next, it produces spores that are extremely durable: whereas the bacterium is destroyed in a relatively short time at 212 F/100 C, the temperature of briskly boiling water at sea level, the spores are not destroyed unless they are subjected to at least 240 F/ 116 C for a sustained length of time. And finally, the bacterium lives and grows in the absence of air (and also in a very moist environment; these combined conditions exist in a container of canned food).
This description does not mention the poison thrown off by the spores as they grow: the toxin is so powerful that one teaspoon of the pure substance could kill hundreds of thousands of people.
The grave illness caused by eating toxin present in preserved food is comparatively rare—rare in relation to the cases of “staph” or salmonellosis—but, unlike them, it is often fatal unless life-support care is given right away. The symptoms are blurred vision, slurred speech, inability to hold up the head, and eventual respiratory arrest unless the victim is given help to breathe until the body can reverse the progress of the illness with the aid of medication. Between 1899 and 1949 the case-fatality rate of food-borne botulism was 60 percent. Since then it has declined markedly and steadily, thanks to quicker diagnosis and great improvements in intensive care at the outset. The case rate took a brief upward spurt in the mid-1970s however, because a whole generation of people went in for food preservation, especially home-canning, without having the information or equipment needed for a safe product.
The botulinum toxin can be destroyed by brisk boiling in an open vessel. This is why, throughout this book, we warn people to boil hard—for the time demanded by its density and acidity—any home-canned food about which there is the slightest safety problem.
C. botulinum is held inactive at freezing and comes into its own at room temperatures, as mentioned earlier. Type E, the comparatively rare food-borne strain that is found on sea- and freshwater seafood, begins to grow at refrigeration temperatures.
As with all micro-organisms, a moisture content of below 35 percent directly inhibits its growth.
DEALING WITH THE SPOILERS
Enter pH—the Acidity Factor
The strength of the acid in any food determines to a great extent which of the spoilage micro-organisms can grow in each food. Therefore acidity is a built-in directive that tells us what temperatures are necessary to destroy these spoilers within it, and make it safe to eat. (Heat alone, not natural acidity, controls the action of enzymes.)
Acid strength is measured on the pH scale, which starts with strongest acid at 1 and declines to strongest alkali at 14, with the Neutral point at 7, where the food is considered neither acid nor alkaline. The pH ratings appear to run backward, since the larger the number, the less the acid, but it may help to think of the ratings as