Alum for Pickling
Alum is used as an ingredient in baking powder and is used to give crispness to pickles and maraschino cherries and to harden gelatin. Alum 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 left in the product amounts to less than 0.2 percent.
According to USDA, if good quality ingredients are used in pickling and up-to-date methods are followed, alum is not needed for crisp pickles. If alum is used in pickling, it is used only in a soak solution. It should be washed off thoroughly before completing the recipe. Do not put alum in the final pickling liquid. Use only food-grade alum. (Douche alum is not food-grade.)
We recommend the use of pickling lime or Ball Pickle Crisp instead of Alum.