A white powder used in older pickle recipes to add crispness. It works by introducing calcium to the pectin of the food to be pickled.
Pickling lime is alkaline, and must be washed off completely before the food is placed in vinegar. Failure to do so could result in a less acidic pickling solution, and create an environment where bacteria are able to thrive. Botulism cases have been linked to this problem; and for this reason, the use of pickling lime is no longer recommended.