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. Now, 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, and household uses, such as oven cleaner and drain opener.

Food uses

Lye is used to cure many types of food, such as lutefisk, green olives, hominy, lye rolls, century eggs, pretzels, zongzi (Chinese glutinous rice dumplings), and Chinese noodles. 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.Lye is a heavy duty alkali at about 13.0 pH.

Controversy

Some manufacturing processes of lye include the processing of salts in mercury vats to create lye. Lye manufactured using this process has been used to make food, such as High Fructose Corn Syrup as outlined in published reports. The concern is that mercury from the vats would find its way into food products, which could lead to mercury poisoning.

Safety

Both solid dry lye and lye solutions are corrosive and will degrade organic tissue.

Hazardous reactions

Solid sodium hydroxide or solutions containing high concentrations of sodium hydroxide may cause chemical burns, permanent injury or scarring, and blindness. Lye may be harmful or fatal if swallowed.

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

Avoid all contact with aluminium. 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 may react with various sugars to generate carbon monoxide, which is a poisonous gas; mixing sodium hydroxide and sugar in a closed container is therefore dangerous.

Lye intoxication can cause esophageal stricture.

Protection

Personal protection for the safe handling of lye includes safety glasses, chemical-resistant gloves, and adequate ventilation. When in the close proximity of lye dissolving in an open container of water, a vapor-resistant face mask is recommended.

Storage

Lye is a deliquescent salt and has a strong affinity for moisture. Lye will deliquesce (dissolve or melt) 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. Lye should be stored in an airtight resealable container.

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.

See also

• Sodium hydroxide, caustic soda
• Potassium hydroxide, caustic potash
• Sodium carbonate, soda ash

Notes

1. McDaniel, Robert (1997).
2. Food Chemicals Codex
3. US Food and Drug Administration
4. Certified Lye
5. [1]
6. [2]
7. Lye Safety Precautions

References