Molds in Canned Goods

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.

in the time after the jar is taken out of its boiling water bath, but before it is filled,

in the time between when the jar is filled and covered with the melted wax,

when the wax cools, if it pulls away from the side of the jar, leaving an opening for the mold to get in, and

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 by Leslie Basel.

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