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From Cecil's Mailbag by the Straight Dope Science Advisory Board
Apr-23-1999
Dear Straight Dope:
What is alum? I see it occasionally in Looney Tunes cartoons, where it is used to make
some poor victim's mouth shrink. Is this stuff real? Where can I get some? --Mike
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 Jill 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.
--SDSTAFF Ken and SDSTAFF Jill
Straight Dope Science Advisory Board
Cecil's Mailbag is researched and written by members of the Straight Dope Science Advisory Board, Cecil's online auxiliary. Although the SDSAB does its best, these articles are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.
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