Reader Amy writes to say that some of her old family recipes call for alum, but what is it and is it really necessary? Great questions. Anyone who’s every watched a Warner Brothers cartoon has probably wondered the something similar. You know those scenes: Tweety Bird somehow manages to pour a box of powdered alum down Sylvester’s the Cat’s throat and his head shrinks up to the size of a golf ball. But what the heck is that stuff and what did people use it for?
Alum is short for aluminum potassium sulfate. It was once a common household item here in the U.S., especially during the war years when people did a lot of home pickling. A pinch of it in a jar of kosher dills or watermelon rinds kept the pickles 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 shrinking or constricting of blood vessels and/or mucous membranes).
How ’bout an answer to the question, digression king? 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. Then again baking powder is a lot easier, which is the reason I prefer it.
Of course any baking powder you buy probably has alum or some close variant of alum in it, so if you’re specifically looking to avoid alum or aluminum itself, there are some non-aluminum baking powders on the market that work pretty well.