Alum is highly astringent crystals of potassium aluminum sulfate. Since it occurred naturally, people across civilisations found many uses of alum.
There are oblique references to alum, sometimes very obscure, dating back at least to two millennia B.C. But the certainty of its actual usage can only be proved by analysing and dating artifacts in which alum had been employed at some stage of their creation.
Alum was mainly used during the last century for mordanting; for tanning and softening leather; for its alleged medicinal and cosmetic properties; and as an auxiliary agent in miscellaneous metal and glass finishes.
Alum occurs naturally in more than one form; but, where it was not readily available, it had to be manufactured.
 Why should I be aware of this?
- Alum is a popular and an easily available ingredient.
- It was used both in the kitchen and in cosmetic applications.
- There are health concerns associated with alum.
- Studies have shown that aluminum sulfates are mildly toxic and higher doses can irritate the skin, eyes, and lungs.
 All about alum
Alum refers to two double salts, potassium aluminum phosphate and ammonium aluminum sulphate. These are usually called common or ordinary alum.
Alum's medical uses are as an astringent, a styptic and an emetic. It can be a dangerous substance when not used properly. Ingestion of 30 grams (1 ounce) has killed adults. Alum is legal to use in baking powders. In pickles and cherries, the amount usually left in the packaged product amounts to less than 0.2 percent. Alum is included in some fermented pickle recipes. Research shows that it has no effect until after the pickles have been fermented. Then it is used only in a soak solution. It should be washed off thoroughly before completing the recipe. Never put alum in the final pickling liquid. Douche alum is not food grade.
Alum has been used in many different fields, including photography, papermaking, medicine, and food preparation.
The main use of alum in the previous century was in food preparation, especially for pickling vegetables like cucumbers and onions. A very small amount of alum (about one quarter of a teaspoon per pint) was added to the brine solution to keep the pickles crisp and crunchy. It was also added to bottled fruits such as maraschino cherries. Alum was also a common component of baking powder. It served as an acid that reacted with a base in the baking powder to form gas that help baked goods rise.
 Alum and health
Alum is not commonly used in food today because of health concerns. Studies have shown that aluminum sulfates are mildly toxic and higher doses can irritate the skin, eyes, and lungs. It can also cause gastrointestinal problems when consumed and may even result in death. Fortunately, most people would have had to consume extremely large amounts of baking powder or pickles that contained alum to be at risk. Most companies decided they didn't want the risk and have stopped using alum in their products. Today, commercial baking powder, pickles, and maraschino cherries do not contain alum.
If you make your own pickles keep in mind there are alternatives to alum. Calcium salts or food-grade lime can be used to keep pickles crisp. However, if you want to not use any chemicals at all, you can simply soak the cucumbers in ice water for several hours before pickling. The cold water also works well to keep the pickles crisp.
Alum also has various medical uses because of its strong astringent property. It can be applied after shaving to soothe the skin. Also, many people swear that putting a small dab of alum on a canker sore a couple times a day helps relieve the pain and helps it to heal faster. Alum will most likely cause the canker sore to burn and may make the mouth pucker from its astringency. If you try this remedy, it is important to rinse your mouth out with water after a few minutes and not swallow the alum. This is because alum is also an emetic when ingested at high doses.
Alum is rarely used today. However, alum can still be found in pharmacies and in spice sections of most supermarkets.
- What is alum?
- In defence of alum