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Introduction
Potassium hydroxide (KOH), also known as caustic potash, is a strong base similar to sodium hydroxide but with potassium as the counterion. It is used in food processing for pH adjustment, as a peeling agent for fruits and vegetables, in the production of cocoa and chocolate (alkalization), and in the processing of certain cereals. It is also used in the production of caramel color and in the refining of edible oils.
Potassium hydroxide is more soluble in water than sodium hydroxide and produces a stronger exothermic reaction upon dissolution. In food applications, potassium hydroxide is often preferred when potassium content is desirable (e.g., in low-sodium products) or when the sodium version would leave an undesirable aftertaste.
CAS Number
1310-58-3
Synonyms
Caustic potash, Potash lye, Potassium hydrate, KOH.
Topic Headings
1. Use in cocoa processing (Dutch process) (paragraph form)
Cocoa beans naturally have a pH of 5.0-5.5 (acidic). In the Dutch process (developed by Coenraad Johannes van Houten in the 19th century), cocoa is treated with an alkali solution, typically potassium hydroxide or potassium carbonate. The cocoa nibs are soaked in 1-3% KOH solution at 70-100°C for 30-90 minutes, then dried and roasted. The alkalization raises the pH of the cocoa to 6.5-8.0. This has several effects: the color darkens to a richer brown or red-brown (depending on the degree of alkalization), the flavor becomes smoother and less bitter, and the cocoa becomes more soluble in water and milk. Dutch-process cocoa is used in hot cocoa mixes, chocolate pudding, brownies, and many baked goods. Compared to sodium hydroxide, potassium hydroxide produces a slightly different flavor profile (less salty) and is preferred for premium cocoa products. The potassium also contributes a small amount of mineral nutrition. The European food additive code for potassium hydroxide is E525.
2. Physical and chemical properties (list form)
• Appearance — White solid (pellets, flakes, or powder); also available as aqueous solution (typically 45-50% w/w).
• Odor — Odorless.
• Molecular weight — 56.11 g/mol.
• Melting point — 360°C.
• Boiling point — 1327°C.
• Solubility in water — 112 g/100 mL at 20°C; 178 g/100 mL at 100°C (extremely exothermic).
• Solubility in other solvents — Soluble in ethanol and methanol; insoluble in ether.
• pH (0.1% solution) — Approximately 13 (strongly alkaline).
• Density — 2.04 g/cm³ (solid); 1.52 g/cm³ for 45% solution.
• Hygroscopicity — Extremely hygroscopic; absorbs moisture and CO₂ to form potassium carbonate.
• Corrosivity — Highly corrosive to skin, eyes, and many metals.
3. Food applications and typical usage levels (list form)
• Cocoa processing (Dutch process) — 1-3% of cocoa weight; raises pH to 6.5-8.0; darkens color; improves solubility.
• Fruit and vegetable peeling — 1-2% KOH solution at high temperature for skin removal (similar to NaOH).
• Olive curing — Used in combination with NaOH or alone for some olive preparations.
• Caramel color production — As a catalyst in Class III and IV caramel.
• Vegetable oil refining — To remove free fatty acids (forms potassium soaps which are more water-soluble than sodium soaps).
• pH adjustment in beverages and sauces — Small amounts (0.01-0.1%) to adjust acidity.
• Processing of cereals and grains — To remove bran in certain traditional preparations.
• Fish processing (lutefisk) — Used in some traditional Scandinavian methods (though sodium hydroxide or sodium carbonate is more common).
4. Regulatory status, safety, and handling (paragraph form)
Potassium hydroxide is approved as a food additive (E525) in the EU and as a GRAS substance by the FDA under 21 CFR 184.1769 (as a pH control agent and processing aid). No ADI is set by JECFA because it is used as a processing aid and residues are either removed or neutralized. For cocoa processing, residual potassium must not exceed 0.1% in the final product. Safety: KOH is similarly hazardous to NaOH; it causes severe burns to skin, eyes, and respiratory tract. In food plants, automated handling and personal protective equipment are mandatory. In the finished food, potassium hydroxide is converted to harmless potassium salts (e.g., potassium carbonate, potassium chloride) or is neutralized by food acids. Compared to sodium hydroxide, potassium hydroxide is more expensive, but it is preferred in low-sodium products and in applications where potassium provides a functional benefit (e.g., in yeast nutrition, since potassium is an essential yeast nutrient). In cocoa, the use of KOH is considered to produce a superior flavor to NaOH. For consumers, products made with KOH are safe when properly processed.
