What is Alum, really?

     Alum is the common name for a salt that is most easily found in the spice sections of some grocery stores. Individuals that are well-versed in home canning principles will recognize the name, since it is a common ingredient in some pickling recipes. It is made by mining bauxite, then refining it into alum.


     Potassium aluminum sulfate, or potash alum, is also half the base of baking powder, another useful cooking ingredient. Baking powder leavens, or raises, quick breads, muffins, and pancakes, without dramatically changing the pH, and therefore taste, that baking soda would. The alum in baking powder is activated as the dough reaches higher temperatures. The other half of baking powder is baking soda (sodium bicarbonate).
     Years ago bakers in England used to add it to their breads, not as a leavening agent, but to make the dough seem whiter. A practice we would abhor now, it has been made illegal there. However, it is not illegal here. It kind of makes you wonder how they 'bleach' flour and make white bread so white.

Personal Care

     Along with aluminum chlorohydrate, it is added to some deodorants as a safe astringent, as it kills odor-causing bacteria. Many people are against the use of alum in this way, since it is possible that it gets absorbed into the skin and contaminates the body. Aluminum compounds supposedly neither hurt nor harm cells, but the science is still out on that opinion. It is known that aluminum can be absorbed from deodorants and can cross the blood-brain barrier.

Leather tanning

     Tanning animal skins is a fairly complex skill. The alum comes in at near the end of the process, where it can be mixed with washing soda, the cleaned, dry skin can either be immersed in the mixture or have it painted on as a paste. Alum is used in tanning to remove moisture, prevent rotting, and produce leather.


     Alum is known to be one of the least toxic of the metallic fabric mordants. A mordant is a chemical used to help to adhere dye to fabric. It is also considered to be the all-purpose mordant, as hand-dyeing is a largely artistic and experimental endeavor with no two results being alike. Iron impurities in alum can change color outcomes, making for a dull piece. Alum is recommended for all protein fibers, like wool, and most cellulose fibers, like hemp. There doesn't seem to be a recommended mordant for cotton.


     Alum is used in pickling recipes to keep the vegetables more crisp. Washington State University says, "Calcium and aluminum salts improve pickle firmness by combining the pectin to make the cucumber more resistant to softening. Alum (aluminum potassium sulfate) has been shown to cause a slight increase in pH and a significant increase in firmness when used at levels up to ¼ teaspoon per pint."
     It can be used in wastewater treatment to 'grab' larger particles, making them sink, which makes them easier to filter from the wasted water.
     Given its wide variety of uses, this little chemical makes a very interesting addition to your preps and pantry.

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