Alum powder is a crystalline powder that is most commonly used in pickling; it keeps pickles firm and crispy.

THIS ALUM WILL NOT GROW CRYSTALS.

Alum powder is often used to firm and crispen pickles by letting them soak in a sealed brine solution of water, vinegar, salt, spices, and alum powder for several weeks. Cucumbers should be pickled at the peak of freshness because they will become soft after a few days. Use up to 1/4 teaspoon of alum per pint of solution.

Alum’s tissue-shrinking properties gave it a starring role in multiple episodes of the cartoon Looney Tunes in which alum was shown to comically shrink the characters’ heads and pucker up lips.