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Canning -- Pickled and Fermented Foods
What is alum?
The two double salts, potassium aluminum phosphate and ammonium aluminum sulphate, are usually called common or ordinary alum. It is used as an ingredient in baking powder and is used to give crispness to pickles and maraschino cherries and to harden gelatin. Alum's medical uses are as an astringent, a styptic and an emetic. It can be a dangerous substance when not used properly. Ingestion of 30 grams (1 ounce) has killed adults. Alum is legal to use in baking powders. In pickles and cherries, the amount usually left in the packaged product amounts to less than 0.2 percent. Alum is included in some fermented pickle recipes. Research shows that it has no effect until after the pickles have been fermented. Then it is used only in a soak solution. It should be washed off thoroughly before completing the recipe. Never put alum in the final pickling liquid. Douche alum is not food grade.