If good equipment and proper technique are used, then it is unlikely you will ever have mold growth in your unopened canned goods. If you do have such, then there was either a flaw in the procedure you used, or something affected the jar or can after the fact to break its seal. In any event, once the food has molded, it is past saving and should be discarded in such a way that children and animals will not be able to get into it. The most likely home canned products to show mold growth are jams and jellies sealed with paraffin wax.
There are a number of points in the canning process where this can occur:
(1) In the time after the jar is taken out of its boiling water bath, but before it is filled.
(2) In the time between when the jar is filled and covered with the melted wax.
(3) When the wax cools, if it pulls away from the side of the jar, leaving an opening for the mold to get in.
(4) If bubbles form in the paraffin, which break and leave holes.
It is for this reason that most canning authorities no longer recommend using this technique. If you must use it, the jelly jars should be boiled for at least 10 minutes before the jelly is poured into the jars. The filled and wax capped jars should then be covered with some sort of protective lid. The book, Putting Food By has excellent instructions on this or see the applicable section of the rec.food.preserving FAQ.
B.3 MOLDS IN GRAINS AND LEGUMES
It's long been known that eating moldy grain is bad for your health. The ugly consequences of eating ergot-infected rye probably make the best known example. It's only been for about thirty years, though, that intensive study of these grain fungi have been carried out on other varieties of molds and their respective mycotoxins. Fortunately, for those of us in the U.S., the USDA and the various state departments of agriculture go to a great deal of trouble to detect grain and legumes infected with these toxic fungi. In some of the less developed countries, the citizenry are not so lucky. Still, it is good to have something of an understanding of what one should do to prevent mold growth in one`s stored grains and to have an idea of what to look for and ask about when purchasing grains and legumes.
The one fungal type that has caused the most commotion in recent history are the various Aspergillus species of molds. Under certain conditions with certain grains, legumes, and to a lesser extent, nuts, they can produce a mycotoxin called aflatoxin. This is a serious problem in some parts of the world, most especially in peanuts, occasionally in corn. I am not aware of any documented deaths in the United States from aflatoxicity, but other nations have not been so fortunate. What makes aflatoxin so worrisome in this country is that it is also a very potent carcinogen (cancer causing agent).
In addition to the Aspergillus molds, there is also a very large family of molds called Fusarium and these can produce a wide variety of mycotoxins, all of which you do not want to be eating directly or feeding to your food animals where you will get the toxins back indirectly when the animal is slaughtered and eaten.
The Federal government and the various state governments continuously monitor food and forage crops. Those products which are prone to mold growth and toxin production are not allowed to be sold for food. Once purchased however, it is up to you to keep your food safe from mold growth. If you have already found mold growth in your whole grains, meals, flours or other grain products, they should be discarded. Most mycotoxins are not broken down or destroyed by cooking temperatures and there is no safe way to salvage grain that has molded.
B.3.1 PREVENTING MOLD GROWTH IN STORED GRAINS AND LEGUMES
The easiest method to prevent mold growth in your stored grains and legumes is simply to keep them too dry for the mold to grow. The Aspergillus and Fusarium molds require moisture contents of 18% and above to reproduce. This is subject to some variability, but in all grains and soybeans, they must have a moisture content of that level. If you are storing raw (not roasted) peanuts, in the shell or shelled, you want to get the moisture content to less than 8% as peanuts are particularly susceptible to mold growth. The recommended moisture content for all other grain and legume storage is no more than 10%. Please see part 2.A.3.1 Grains and Legumes for a method to determine moisture content. At 10% moisture, it is simply too dry for fungi to grow..
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Revised: 1 Dec 99