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E524 Sodium hydroxide (Caustic soda)

E524Acidity regulatorsOrigin: Lab-made
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The short answer
Sodium hydroxide (E524), also called lye or caustic soda, is a strong base that darkens pretzels, mellows olives and cocoa. It is dangerous in its pure form, but food makers rinse or neutralize it, so safe foods keep only harmless sodium salts.
Generally safe

Fine for most people at normal amounts.

E-numberE524
Comes fromLab-made
What it doesAcidity regulators
Glycemic index—
Daily limitNot set
Also calledE524, Lye

Rules by country

🇺🇸 US FDAApproved
🇪🇺 European UnionApproved
🇨🇦 Health CanadaApproved
CaliforniaNo extra rules

Permitted in the US, EU and Canada as a processing aid and acidity regulator. It is used to make pretzels and olives milder or darker, and in some cocoa processing.

Daily limit: Experts haven’t set a number because normal food amounts are far below any level of concern.

What is it?

Sodium hydroxide raises the pH of a food, which changes its color, taste and texture. In a pretzel bath it browns the crust, and in an olive cure it breaks down the bitter compounds that make raw olives unpleasant.

Where it comes from: Made by splitting salt water with electricity in chlor-alkali plants. Pure sodium hydroxide is extremely caustic, so food makers use it in small amounts and rinse or neutralize it. The finished food keeps only sodium salts.

Why it’s in food

  • Gives pretzels their dark brown crust
  • Removes bitterness from olives
  • Darkens and mellows some cocoa
  • Loosens the skin of canned peaches and tomatoes in factories

Often found in

PretzelsCanned black olivesDutch-process cocoaCanned peaches

Also listed as: E524, Lye, Soda lye

Health & gut impact

BurnsConcern

Solid and concentrated lye burn skin and eyes. Factories handle it with protective gear, and home cooks should wear gloves when they make a pretzel bath.

FDA 21 CFR 184.1763

SodiumConcern

The amount of sodium from this processing aid is small compared with table salt, because most of it leaves with the rinse water.

FDA 21 CFR 184.1763

What can I use instead?

Baking soda (E500)

Ratio: Not a swap: baking soda browns pretzels less

Best for: Milder home pretzel dips

Potassium carbonate (E501)

Ratio: Varies by process

Best for: Alkalizing cocoa

Related

More acidity regulators:

Acetic acid E260Acetic acid (E260) is the acid that makes vinegar sour. Diluted in food it is considered safe. The hazard is the concentrated factory form, not a splash of vinegar.Generally safeAmmonium carbonate E503Ammonium carbonate (E503) is a traditional leavening agent that makes thin cookies and crackers crisp. It breaks down into gas in the oven, so little of it stays in the finished food.Generally safeCalcium carbonate E170Calcium carbonate (E170) is ground limestone, the same calcium found in antacids. It adds calcium to plant milks and flour and is very safe.Generally safeCalcium chloride E509Calcium chloride (E509) is a salty calcium salt that firms tofu, cheese curds and pickles. It is considered safe at food doses. Too much tastes bitter, which is why recipes use a little.Generally safe

Common questions

Is lye in food dangerous?

Concentrated lye is dangerous, but the amount in food is small and is rinsed or neutralized during processing. Foods that list sodium hydroxide are considered safe at those levels.

Is sodium hydroxide vegan?

Yes. It is made from salt and water by an industrial process, with no animal ingredients.

Is Sodium hydroxide safe?

Generally safe (86/100). Permitted in the US, EU and Canada as a processing aid and acidity regulator. It is used to make pretzels and olives milder or darker, and in some cocoa processing.

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Scientific sources & regulatory citations
  • 21 CFR 184.1763 (US FDA)
  • EFSA OpenFoodTox: E524
  • FDA 21 CFR 184.1763

INS 524 · CAS 1310-73-2