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Introduction
Ammonium hydroxide (NH₄OH) is an aqueous solution of ammonia gas (NH₃) in water. It is a weak base used in food processing as a pH adjuster, as a leavening agent (source of ammonia for baking), and in the production of certain caramel colors. It is also used as a cleaning agent in food facilities. The characteristic pungent odor of ammonia is detectable even at low concentrations.
In baking, ammonium hydroxide is used as a component of baker's ammonia (ammonium carbonate or ammonium bicarbonate), which decomposes to ammonia and carbon dioxide when heated, leaving no residue. This makes it ideal for thin, crisp products like crackers and cookies where other leavening agents would leave mineral residues.
CAS Number
1336-21-6 (aqueous solution). Anhydrous ammonia: 7664-41-7.
Synonyms
Aqua ammonia, Ammonia water, Ammonia solution, Ammonium hydrate, E527 (EU).
Topic Headings
1. Use as a leavening agent: baker's ammonia (paragraph form)
Baker's ammonia (ammonium carbonate or ammonium bicarbonate) is often prepared by reacting ammonium hydroxide with carbon dioxide. When added to dough or batter and heated above 60°C, it decomposes completely: NH₄HCO₃ → NH₃ + CO₂ + H₂O. Both ammonia and carbon dioxide gases expand, creating a light, porous structure. Unlike sodium bicarbonate (baking soda) which leaves sodium salts, baker's ammonia leaves no residue because the gases escape. This is particularly important for thin products like crackers, cookies, and some European pastries (e.g., German Lebkuchen, Swedish drömmar). If too much is used, a residual ammonia smell may remain, which dissipates upon cooling or after a few days of storage. Ammonium hydroxide itself can be used directly as a leavening aid when combined with an acid, but the solid ammonium bicarbonate is easier to handle. Today, ammonium hydroxide is still used in some large-scale cracker production facilities where the characteristic crispness and lack of mineral aftertaste are desired.
2. Physical and chemical properties (list form)
• Appearance — Colorless liquid (concentrated solutions have strong ammonia odor).
• Odor — Pungent, characteristic ammonia smell.
• Molecular weight — 35.05 g/mol (NH₄OH).
• Boiling point — Decomposes upon heating; ammonia gas evolves above 38°C.
• Solubility — Miscible with water in all proportions.
• pH (1% solution) — Approximately 11.5 (weak base).
• Density — 0.88-0.91 g/cm³ for concentrated solutions (28-30% NH₃).
• Vapor pressure — High; releases NH₃ gas at room temperature.
• Corrosivity — Corrosive to copper, brass, and zinc.
3. Food applications and usage levels (list form)
• Baking (as ammonium bicarbonate leavening) — Typically 0.5-2% of flour weight for crisp products; ammonium hydroxide itself is less common but can be used in liquid leavening systems.
• Caramel color production (Class III and IV) — As a reactant in ammonium caramel.
• pH adjustment in food processing — Small amounts (0.01-0.1%) to raise pH of solutions; used in some cheese products and cocoa processing.
• Beef and poultry processing — As an antimicrobial agent in ground beef (historically used by some suppliers as a "pink slime" reducer, but controversial; largely discontinued).
• Food equipment cleaning — As a degreaser and sanitizer in CIP systems.
• Fermentation processes — As a nitrogen source for yeast in some industrial fermentations (though ammonium sulfate is more common).
4. Regulatory status and safety concerns (paragraph form)
Ammonium hydroxide is approved as a food additive (E527) in the EU for use as a pH regulator. In the USA, it is GRAS under 21 CFR 184.1839 (as a direct food additive). JECFA has not set an ADI because it is used as a processing aid and volatile. The main safety concern is the toxicity of ammonia gas. Concentrated ammonium hydroxide solutions (above 10% NH₃) are corrosive to skin, eyes, and respiratory tract. In food production, workers must use ventilation and protective equipment. For consumers, properly baked products contain no residual ammonia because the gas escapes during baking. However, if underbaked or if too much is used, a residual ammonia odor and taste may be present, which is unpleasant but not toxic. In 2010, the use of ammonium hydroxide in beef processing (for antimicrobial purposes) received negative media attention; many fast-food chains discontinued sourcing beef treated with ammonium hydroxide. As a result, this application has largely been abandoned. In caramel color, ammonium hydroxide is still used, and the final product contains trace levels of ammonia derivatives (including 4-methylimidazole, which is a concern at high levels). Overall, ammonium hydroxide is safe when used appropriately, but its applications are specialized and declining.
