Safely Prepared Food
How can I ensure that my food is safely prepared?
Botulism (from the Botulinum Spore), is a deadly form of food poisoning that is caused by growth of bacteria on food. Botulism exists as spores or cells; the spores can survive for many years in soil and be harmless, however when the proper conditions exist those spores reproduce into cells which multiply very quickly. All of those cells combined create a deadly toxin.
This environment is most common in a moist, low acidic food at a temperature of 40° to 120°F and that has an oxygen level of less than 2%.
Botulinum spores are found on most fresh food, but because they can not grow with oxygen or high acidic levels they are harmless. These spores, in addition to other bacterias, molds and yeasts are very hard to remove from food surfaces. You get rid of very few of these spores by washing your food alone. If a product is grown underground then you can reduce a great number of them by peeling and/or blanching, but that still does not get rid of all of them. The only way to ensure that you are safe from them is to make sure that you follow the proper directions and processing times of all food types. The best resource for this is the USDA’s Complete Guide to Home Canning.
The processing times in this book ensure destruction of the largest expected number of heat-resistant microorganisms in home-canned foods. Properly sterilized canned food will be free of spoilage if lids seal and jars are stored below 95°F. Storing jars at 50° to 70°F enhances retention of quality.
Whether food should be processed in a pressure canner or boiling-water canner to control botulinum bacteria depends on the acidity of the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods are not acidic enough to prevent the growth of these bacteria. Acid foods contain enough acid to block their growth, or destroy them more rapidly when heated. The term “pH” is a measure of acidity; the lower its value, the more acid 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 mixtures of low-acid and acid foods also have pH values above 4.6 unless their recipes 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’s, 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° to 250°F, attainable with pressure canners operated at 10 to 15 PSIG. PSIG means pounds per square inch of pressure as measured by gauge. The more familiar “PSI” designation is used hereafter in this publication (the Complete Guide to Home Canning). At temperatures of 240° to 250°F, the time needed to destroy bacteria in low-acid canned food 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. The time needed to safely process low-acid foods in a boiling-water canner ranges from 7 to 11 hours; the time needed to process acid foods in boiling water varies from 5 to 85 minutes.
Acidity of Foods
Process adjustments at high altitudes.
Boiling Point Of Water (Image from HFP)
Using the process time for canning food at sea level may result in spoilage if you live at altitudes of 1,000 feet or more. Water boils at lower temperatures as altitude increases. Lower boiling temperatures are less effective for killing bacteria. Increasing the process time or canner pressure compensates for lower boiling temperatures. Therefore, when you use the Complete Guide to Home Canning, select the proper processing time or canner pressure for the altitude where you live. If you do not know the altitude, contact your local county Extension agent. An alternative source of information would be the local district conservationist with the Soil Conservation Service.
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