Lye is the common name of various alkaline solutions, including soda lye (a solution of sodium hydroxide) and potash lye (a solution of potassium hydroxide). Lyes are used as cleaning products, as ingredients in soapmaking, and in various other contexts.
History The word lye derives from the root *lau, meaning to wash (compare lave, lather) and has cognates in all the Germanic languages. Traditionally, lye was made by leaching of wood ashes in water, creating an alkaline liquor rich in potassium carbonate. The alkalinity could be increased by the addition of slaked lime, which would cause the solute to become potassium hydroxide or caustic potash. Indigenous peoples of the Americas used lye in food processing and in the consumption of certain plant products. In particular, lye was employed in nixtamalization, the treatment of maize with an alkaline solution that improves processing characteristics and increases nutrient bioavailability. Depending on local resources, lye was produced from wood ashes, which yield potash-rich alkaline solutions, or from lime produced by calcining limestone or marine shells and subsequently slaking the resulting quicklime. In some regions, mixtures of ash and lime were also used for maize processing. In the Andes, alkaline materials such as plant ashes, lime derived from burned shells or limestone, or mixtures of ash and lime (called llipta in Peru) were also consumed since prehistoric times together with coca leaves. The alkali raises oral pH and enhances the release and absorption of coca alkaloids through the oral mucosa.
Uses
Food preparation
Lyes are used to cure many types of food, including olives and cocoa (making them less bitter), canned mandarin oranges, lye rolls, century eggs, pretzels, candied pumpkins, and bagels. Lye is the curing agent and namesake of the traditional Nordic lutefisk, a type of preserved fish. They are also used as a tenderizer in the crust of baked Cantonese moon cakes, in "zongzi" (glutinous rice dumplings wrapped in bamboo leaves), in chewy southern Chinese noodles popular in Hong Kong and southern China, and in Japanese ramen noodles. In the Philippines, lye is used in the making of kutsinta, a type of rice cake, and pitsi-pitsî. In Assam, extensive use is made of a type of lye called khar in Assamese and karwi in Boro, which is obtained from the ashes of banana stems, roots, and skins. It is used in cooking, curing, as medicine, and as a substitute for soap. Lye made out of wood ashes is also used in the nixtamalization process of hominy corn by the tribes of the Eastern Woodlands in North America. Chocolate was first dutched using lye as a way to alkalize the cacao bean. In the United States, food-grade lye must meet the requirements outlined in the Food Chemicals Codex, as prescribed by the Food and Drug Administration. Lower grades of lye that are unsuitable for use in food preparation are commonly used as drain cleaners and oven cleaners.
Soap making Both sodium hydroxide and potassium hydroxide are used in making soap. Potassium hydroxide soaps are softer and more easily dissolved in water than sodium hydroxide soaps. Sodium hydroxide and potassium hydroxide are not interchangeable in either the proportions required or the properties produced in making soaps. "Hot process" soap making also uses lye as the main ingredient. Lye is added to water, cooled for a few minutes and then added to oils and butters. The mixture is then cooked over a period of time (1–2 hours), typically in a slow cooker, and then placed into a mold.
Cosmetics Lye, like other hydroxide-based products, is also used as a hair relaxer and straightener. Lye relaxers break a third of the chemical bonds in the hair strand and cause the hair to swell. Rinsing and then heating the hair straightens the strands. Due to their high pH, they often cause scalp irritation. Though no-lye solutions, which use guanidine or lithium hydroxide, produce less scalp irritation, they may cause brittleness due to calcium deposits. People of African descent have used lye to relax or straighten hair since the nineteenth century. Black men used lye-based formulations to conk their hair, and black entrepreneurs sold such formulations under names like Konkalene; The Autobiography of Malcolm X includes an account of Malcolm X receiving his first lye conk. The Johnson Products Company introduced industrially produced lye-based relaxers for African American salon hair care in the 1950s; Ultra Wave was marketed to men and Ultra Sheen was marketed to women, and the company represented 80% of the chemical relaxer market through the 1960s. In 1971, Johnson Products became the first black-owned company on the American Stock Exchange.
Industrial processes A number of alkaline substances including sodium hydroxide have been used to adjust the pH during factory processes. It is regularly used to make fruit juices alkaline so that the pulp and sediment will clump, or form flocs, and can be removed. This results in a clear fruit juice that has been clarified. Due to low cost, it has been the main way that chicken scalding tanks are kept sanitary, with an added benefit that it helps the feathers come off.
Cleaning
Lyes are also valued for their cleaning effects. Sodium hydroxide is commonly the major constituent in commercial and industrial oven cleaners and clogged drain openers, due to its grease-dissolving abilities. Lyes decompose greases via alkaline ester hydrolysis, yielding water-soluble residues that are easily removed by rinsing.
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