Lye

For other uses, see Lye (disambiguation).

Lye is a corrosive alkaline substance, commonly sodium hydroxide (NaOH, also known as "caustic soda") or historically potassium hydroxide (KOH, from hydrated potash). Previously, lye was among the many different alkalis leached from hardwood ashes. Today lye is commercially manufactured using a membrane cell method.

Solid dry lye is commonly available as flakes, pellets, microbeads, and coarse powder. It is also available as solution, often dissolved in water. Lye is valued for its use in food preparation, soap making, biodiesel production, household uses, such as oven cleaner and drain opener, and the clandestine production of the drug methamphetamine.

File:Lye.jpg

Canister of solid dry lye.

Food uses

Lye is used to cure many types of food, such as lutefisk, black olives, canned mandarin oranges, hominy, lye rolls, century eggs, and pretzels. It is also used as a tenderizer in the crust of baked Cantonese moon cakes, and in lye-water "zongzi" (glutenous rice dumplings wrapped in bamboo leaves), in chewy southern Chinese noodles popular in Hong Kong and southern China, and in Japanese ramen. In the United States, food-grade lye must meet the requirements outlined in the Food Chemicals Codex (FCC), as prescribed by the U.S. Food and Drug Administration (FDA). Lower grades of lye are commonly used as drain openers and oven cleaners and should not be used for food preparation.

Safety

Lye is a strong alkali, producing highly basic solutions. Both wet lye and dry lye solutions are highly caustic and may cause chemical burns, permanent injury or scarring, and blindness. Lye may be harmful or fatal if swallowed.

Hazardous reactions

This image shows the effects of lye upon human skin. Chemical burns of this type can be extremely painful.

Solvation of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables.

The combination of aluminium and sodium hydroxide results in a large production of hydrogen gas: 2Al(s) + 6NaOH(aq) → 3H₂(g) + 2Na₃AlO₃(aq). Hydrogen gas is flammable; mixing lye (sodium hydroxide) and aluminium in a closed container is therefore dangerous. In addition to aluminium, lye (sodium hydroxide) may also react with magnesium, zinc (galvanized), tin, chromium, brass, and bronze to produce hydrogen gas and is therefore dangerous.

Lye intoxication can cause esophageal stricture.

Protection

Personal protective equipment including safety glasses, chemical-resistant gloves, and adequate ventilation are required for the safe handling of lye. When in proximity to lye that is dissolving in an open container of water, the use of a vapor-resistant face mask is recommended. Be aware that adding too much lye to water too quickly can cause the solution to boil and 'spit'. Abstaining from protection can result in serious injuries.

Storage

Lye is a deliquescent salt and has a strong affinity for moisture. Lye will deliquesce (dissolve ) when exposed to open air. It will absorb a relatively large amount of water from the atmosphere (air) if exposed to it. Eventually, it will absorb enough water to form a liquid solution because it will dissolve in the water it absorbs.

Hygroscopic substances are often used as desiccants to draw moisture away from water-sensitive items. Desiccants should never be placed inside a canister of lye because lye has much stronger hygroscopic properties than activated carbon and silica gel (the most common ingredients in commercial desiccant packets) and will pull and absorb the water from the desiccant packets.

Lye should be stored in air-tight plastic containers. Glass should never be used for storage as lye will slowly eat away at this material. The containers should be labeled to indicate the potential danger of the contents and stored away from children, pets, heat, and moisture.

Soap making

Both sodium hydroxide and potassium hydroxide are used in soap making. Sodium hydroxide is often used to make solid soap while potassium hydroxide is used to make liquid soap. Soaps made of potassium hydroxide are softer and can more easily be dissolved in water than sodium hydroxide soaps.

When used in making soap, sodium hydroxide cannot be substituted for potassium hydroxide and vice versa because soap making recipes will have different quantity requirements for these two chemicals depending on the kind of soap being manufactured. In addition, the quantities required for soap saponification differ when using caustic soda and hydrated potash.

References

• "Federal Food, Drug, and Cosmetic Act". US Food and Drug Administration.
• "Food Chemicals Codex". United States Pharmacopeia.
• "Lye Safety Precautions". Certified Lye.
• "NaOH MSDS".
• "Lye. An example of sodium".

• McDaniel, Robert (1997). The Elegant Art of Handmade Soap: Making, Scenting, Coloring, and Shaping. Iola, WI: Krause Publications. ISBN 0-87341-832-8.