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E524AcidulantLow concern
Sodium Hydroxide
In plain words
The short version
Caustic soda — a strong base used for pH adjustment, pretzel browning, and olive curing.
Why it's green
It's widely considered safe at the amounts used in food, so we mark it green. The Safety section below has the details.
Safety profile
ADI not specified — neutralized to harmless sodium salts during food processing. The pure material is highly corrosive (strong base) so it is a workplace-safety hazard, not a consumer hazard. Final food products contain only trace residual.
The detail
Manufactured industrially by electrolysis of sodium chloride brine (chlor-alkali process). One of the highest-tonnage industrial chemicals; food-grade material meets strict heavy-metal purity criteria.
Used as a processing aid for pretzel and bagel browning (a brief dip in dilute lye solution before baking creates the characteristic dark crust), in lye-cured olives (removes oleuropein bitterness), in Dutch-processed cocoa (alkalinizes the beans), and in some Asian noodles (kansui). Functions as a pH adjuster across many product categories at low residual levels.
White solid (pellets or flakes), extremely hygroscopic and deliquescent. Dissolves exothermically in water. Strong base (pH 14 in 1 M solution).
Permitted globally as a processing aid and pH regulator. Residual must be neutralized in the final product.
Sources
- WHO JECFA database — Sodium hydroxide, INS 524 (evaluation 1965, 9th meeting) — World Health Organization / JECFA, 1965. No numerical ADI (ADI 'not limited')
- US eCFR — 21 CFR 184.1763 Sodium hydroxide (GRAS) — US FDA / Office of the Federal Register (eCFR), 2026. US GRAS as pH control agent and processing aid
- European Commission food additives database — Sodium hydroxide, E 524 (Union list, Group I and group E 524–528) — European Commission, DG SANTE, 2026. EU authorisation (Group I; pH adjustment in infant/baby foods)
Checked against these sources on .
Educational information only. Not medical, dietary or veterinary advice. Spotted an error? Tell us.