BOTULISM. One of the most notorious of the spore-forming bacteria is Clostridium botulinum. When growing in food this bacteria can produce a deadly poison which causes botulism, a deadly illness. The mortality rate is 56 percent. This bacteria and its spore are present in soil throughout the world and as a result contaminates most of the food we eat. But the spore only germinates and grows where there is suitable food, no air, and a pH above 4.6. These conditions exist in canned low acid foods.
To assure botulism-free home-canned foods, it is absolutely essential that low-acid foods be canned in a pressure canner at temperatures above 212° F. The poison produced by this bacteria is one of the most potent poisons known to humans. It has been estimated that 1 cup (8 ounces) is sufficient to kill all the humans on earth. It is not something to take chances about. All home canning procedures recommended by Federal and State Extension agencies are adequate to destroy this dreaded spore-forming bacteria.
pH VALUE OF VARIOUS FOODS
| High Acid | |
|---|---|
| 2.9 | plums |
| 3.0 | gooseberries |
| 3.2 | dill pickles, apricots |
| 3.3 | apples, blackberries |
| 3.4 | sour cherries, peaches |
| 3.5 | kraut, raspberries |
| 3.7 | blueberries |
| 3.8 | sweet cherries |
| 3.9 | pears |
| 4.3 | tomatoes |
| 4.6 | ———— |
| Low Acid | |
| 4.8 | okra |
| 5.0 | pumpkins, carrots |
| 5.1 | turnips |
| 5.2 | beets, string beans |
| 5.4 | sweet potatoes |
| 5.5 | spinach, asparagus |
| 5.6 | baked beans |
| 5.7 | red kidney beans |
| 5.9 | lima beans |
| 6.0 | succotash |
| 6.2 | peas |
| 6.3 | corn |
| 7.0 | hominy, ripe olives |
Commercial canneries, which are regulated by the Food and Drug Administration, use similar processes to assure safe canned foods. In the past 50 years, 75 percent of the reported cases of botulism in the United States have been caused by home-canned food while less than 10 percent have been caused by commercially canned food. If proper home-canning procedures are followed, botulism from this source could virtually be eliminated as a cause of death in the US.
On the lower side of pH 4.6, acid content of the food will prevent growth of Clostridium botulinum and most of the other spore-forming bacteria. Thus, these foods can be preserved by using a lower heat treatment. The most common types of spoilage micro-organisms associated with acid foods are yeasts and molds. These organisms are acid-tolerant and can grow in an acid environment. They are killed at a lower temperature than spore-forming bacteria. Acid foods only need a heat treatment in a boiling water bath for a specified time to destroy the microbes present.
Fermentation
Preservation of food by controlling the acid content can be achieved in two ways. One is to naturally ferment the food—turning cabbage into sauerkraut. The other is to add an organic acid to the food to reduce the pH—adding vinegar to cucumbers to make pickles. Some foods such as berries and fruits naturally contain enough organic acids so their pH is below 4.6, and preservation of these foods requires only a boiling water bath heat treatment or freezing.
In a natural fermentation, lactic acid bacteria convert fermentable carbohydrates in the food to lactic acid. In this way the pH is reduced and most bacterial growth inhibited. When cabbage is fermented to sauerkraut, the cabbage’s pH is reduced from pH 6.8 during the fermentation to less than 3.5. Cucumbers can also be fermented to pickles by a similar process; however, most pickles are made by direct acidification of the cucumbers.