Potassium hydroxide
A strong alkali used in tiny amounts to raise the pH of foods during processing. It reacts away and does not remain as free alkali in the finished product.
What is it?
Potassium hydroxide is a strong inorganic alkali (also called caustic potash). In food use it appears as a dilute solution or solid that dissolves readily in water. It is the potassium analogue of sodium hydroxide (lye, E524).
What does it do?
It neutralises acids in food systems, raising pH to the desired level. Because it reacts chemically with the food matrix, the hydroxide ion is consumed during processing and the finished product contains potassium salts rather than free alkali. It can also saponify fats and soften cell walls, which is why it is used in olive curing and pretzel glazing.
Where you will see it
Dutch-process (alkali-treated) cocoa powder, where it darkens colour and smooths flavour. Cured olives, where a lye bath softens the flesh and removes bitterness. Glazed pretzels and lye rolls, giving the characteristic chewy crust and brown colour. Some noodles and ramen, adjusting dough pH for texture. Certain cheeses and processed dairy products as a pH adjuster. On a label it appears as 'potassium hydroxide' or 'acidity regulator (E525)'.
What the science says
Behaviour in food: does any free alkali remain?
Potassium hydroxide reacts rapidly with food acids, proteins, and fats. Studies of lye-treated foods consistently show that free hydroxide is neutralised during processing, and the pH of finished products falls back toward neutral. At typical use levels the body receives potassium salts, not caustic alkali.
EFSA's Panel on Food Additives and Nutrient Sources (ANS) concluded that potassium hydroxide, used as a food additive at quantum satis, does not raise a safety concern at the levels technologically needed, and set no numerical ADI.
Potassium intake from food use
The potassium released when potassium hydroxide neutralises food acids contributes to dietary potassium intake. For healthy people this is not a concern and potassium is an essential mineral. People with kidney disease who must limit potassium intake should be aware that alkali-processed foods can be a minor additional source, though the contribution from E525 at food use levels is small.
Individuals with chronic kidney disease are advised by NHS guidance to limit potassium from all dietary sources, including processed foods treated with potassium salts.
Where it stands with the regulators
Who should be careful
People with chronic kidney disease who are on a potassium-restricted diet should take note that foods processed with potassium hydroxide contribute additional potassium. Look for 'potassium hydroxide' or 'acidity regulator (E525)' on the label.
The honest read
Potassium hydroxide has been used in food preparation for centuries, most visibly in olive curing and pretzel baking. Its chemistry is well understood: it is a strong base that reacts with and is consumed by the food it treats, leaving potassium salts behind rather than free caustic alkali. There is no credible body of evidence linking it to cancer, hormone disruption, or any systemic health effect at the levels found in food. The only genuine dietary consideration applies to people managing kidney disease, for whom potassium from all sources accumulates. Outside that group, the additive is chemically unremarkable in the finished food.
Related additives
Common questions
Is E525 banned in the UK?
No. Potassium hydroxide (E525) is approved for food use in the UK under the FSA approved-additives list and assimilated EU Regulation 1333/2008. It is permitted at quantum satis levels as an acidity regulator.
Is potassium hydroxide the same as lye?
Lye traditionally refers to sodium hydroxide (E524), though potassium hydroxide is also called caustic potash and is closely related. Both are strong alkalis used in food processing; potassium hydroxide is used where a potassium rather than sodium source is preferred, for example in some cocoa and baking applications.
What foods contain E525?
Dutch-process cocoa powder, cured olives, lye-glazed pretzels and bread rolls, some ramen and Asian noodles, and certain processed dairy products. It appears on the label as 'potassium hydroxide' or 'acidity regulator (E525)'.
Is E525 vegan?
Yes. Potassium hydroxide is a mineral-derived inorganic compound with no animal-derived ingredients.
Sources
- Approved additives and E numbers | Food Standards Agency
- EFSA ANS Panel: Re-evaluation of hydroxides (E524, E525, E526, E527, E528, E529) as food additives
- NHS: Chronic kidney disease - eating and drinking
- EU Regulation 1333/2008 on food additives (Annex II)
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