Lye

Lye refers to alkaline solutions like soda lye (sodium hydroxide) and potash lye (potassium hydroxide). Its name comes from the root lau, meaning "to wash," a word shared across Germanic languages. Traditionally, lye was produced by soaking wood ashes in water, creating a potassium carbonate-rich liquid. Adding slaked lime boosted its alkalinity, turning it into potassium hydroxide (caustic potash).

Indigenous peoples of the Americas used lye in food processing, notably for nixtamalization—treating maize with an alkaline solution to improve processing and nutrient absorption. They made lye from wood ashes, lime from heated limestone or shells, or mixtures of both. In the Andes, alkaline substances like plant ashes, lime, or ash-lime blends (called llipta in Peru) were consumed with coca leaves to raise oral pH and enhance alkaloid absorption.

Food preparation

Lye cures many foods, such as olives, cocoa, canned mandarin oranges, lye rolls, century eggs, pretzels, candied pumpkins, and bagels. It gives its name to Nordic lutefisk and tenderizes baked Cantonese moon cakes, zongzi, chewy southern Chinese noodles, Japanese ramen, and Philippine kutsinta and pitsi-pitsî. In Assam, lye called khar or karwi comes from banana stem ashes and is used in cooking, medicine, and as soap.

Eastern Woodlands tribes use wood-ash lye for nixtamalization. Dutching chocolate involves alkalizing cocoa beans with lye. In the U.S., food-grade lye must meet Food Chemicals Codex standards; lower grades are used for drain and oven cleaners.

Soap making

In soapmaking, sodium hydroxide and potassium hydroxide produce different soaps: potassium soaps are softer and more water-soluble. They aren't interchangeable in recipes. Hot-process soapmaking combines lye with water, then oils and butters, cooked for one to two hours before molding.

Cosmetics

Lye is a hair relaxer and straightener, breaking about a third of hair bonds and causing swelling, then straightened by rinsing and heating. Its high pH often irritates the scalp. No-lye alternatives using guanidine or lithium hydroxide cause less irritation but can lead to brittleness from calcium deposits.

Since the nineteenth century, people of African descent have used lye to relax hair; black men used it for conks, and products like Konkalene were sold. Johnson Products introduced industrial lye relaxers in the 1950s—Ultra Wave for men, Ultra Sheen for women—dominating 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

Industrially, sodium hydroxide adjusts pH, clarifying fruit juices by clumping pulp and sediment. It keeps chicken scalding tanks sanitary and helps remove feathers. For cleaning, sodium hydroxide is a key ingredient in oven and drain cleaners, breaking down grease through alkaline ester hydrolysis into water-soluble residues.

Lye also digests animal tissues via alkaline hydrolysis: a carcass is placed in a sealed chamber with lye and water, then heated. After hours, only a coffee-like liquid and fragile bone remnants remain.