Reader Jess writes to say that some of her old family recipes call for alum, but what is it? And is it really necessary? Great questions, Jess. Anyone who’s every watched old Warner Brothers cartoons has probably wondered something similar. You know, when Tweety Bird pours a box of alum down Sylvester’s throat and his head shrinks down to the size of a golf ball. What is that alum stuff and why did people keep it around?
“Alum” is short for aluminum potassium sulfate. It was once a common household item, especially during the war years when people did a lot of home pickling. A pinch of alum in a jar of kosher dills or watermelon rinds kept them firm and crispy. Too much and the result was a serious pucker, since alum is both an acid and an astringent (which is to say, a compound that causes the constricting of mucous membranes and blood vessels).
How ’bout an answer to the question, digression king?
Ah right. Alum has another household use: as a chemical leavener. It’s commonly formulated into baking powders as a reactant along with baking soda. This is probably why it appears in your family’s recipe, Amy. Is it strictly necessary? No. You can use some other form of kitchen acid to create your reaction if you like: a little cream or tartar or a teaspoon or two of vinegar or fresh lemon juice will do the trick.