What is alum, and will it make someone’s mouth shrink, like in the cartoons?

SDStaff Ken replies:

From my dictionary, which was bought when Looney Tunes were new:

alum – a double sulfate of of ammonium or a univalent metal (such as sodium or potassium) and a trivalent metal (such as aluminum, iron or chromium): it is used as an astringent, as an emetic and in the manufacture of baking powders, dyes and paper; the commonest form is potash alum (potassium aluminum sulfate).

An astringent would cause the shrinkage of tissue (hence its popularity in cartoons). We can thank our lucky stars that the censors wouldn’t allow the animators to show its use an an emetic (inducing vomiting).

SDStaff Jillgat replies:

My first experience with this stuff was when I got some for making play dough with my kids. Since I’d never used it for anything before and it was found in the spice aisle, I gave it a taste. WHOA! Bad idea. Shoulda paid attention to Bugs.

Cake alum, pickle alum, filter alum, papermaker’s alum and pearl alum are other common names of aluminum sulfate, which occurs in nature as the mineral alunogenite. The substance irritates the eyes, the skin and the respiratory tract, and is corrosive on ingestion, according to the International Chemical Safety Card from the Centers for Disease Control and Prevention. It can be a dangerous substance when not used properly. Ingestion of 30 grams (1 ounce) has killed adults. Huh. And you find it right next to the allspice.

According to the National Food Safety Database, alum is used as an ingredient in baking powder and is used as a crisping agent in the production of pickles and maraschino cherries. It is used only in a soak solution and is washed off thoroughly before completing the recipe. It is also used to harden gelatin. Alum’s medical uses are as an astringent, a styptic and an emetic. Some people say that placing a small piece of alum on a cold sore causes healing to take place much faster, but I wouldn’t do that myself.

The USDA says that using alum to firm fermented pickles is unnecessary, and that food-grade lime can be used instead. But lime has its hazards too. Excess lime neutralizes or removes acidity and so must be washed out to make safe pickles, and the cucumbers must be rinsed and re-soaked in fresh water.

By the way, the alum didn’t have the effect on me that it does on the people in the cartoons. I still have a big mouth.

SDStaffKen, Straight Dope Science Advisory Board

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