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Introduction
Ammonium sulfate ((NH₄)₂SO₄) is an inorganic salt widely used in food processing as a dough conditioner and yeast nutrient. It provides a source of ammonium ions for yeast metabolism, promoting vigorous fermentation in bread and baked goods. The sulfate component also contributes to dough acidity, which strengthens gluten structure.
In addition to its role in baking, ammonium sulfate is used as a firming agent in some vegetable products and as a processing aid in the production of caramel color (Class III and IV). It is generally recognized as safe (GRAS) by the FDA when used according to good manufacturing practices. Ammonium sulfate is also a common fertilizer, but food-grade purity is required for food applications.
CAS Number
7783-20-2
Synonyms
Ammonium sulphate, Diammonium sulfate, Sulfuric acid diammonium salt, (NH₄)₂SO₄.
Topic Headings
1. Mechanism of action as a yeast nutrient in bread making (paragraph form)
Yeast requires a source of assimilable nitrogen for protein synthesis and cell multiplication during fermentation. In dough systems, the available free amino acids and ammonium ions are often limited, especially in white flour with low protein content. Ammonium sulfate dissociates into ammonium ions (NH₄⁺) and sulfate ions (SO₄²⁻). Yeast cells take up NH₄⁺ via ammonium transporters (Mep proteins) and incorporate it into glutamine and glutamate through the glutamine synthetase-glutamate synthase pathway. This increases yeast growth rate and fermentation activity, producing more carbon dioxide and improving dough rise. Typical usage levels in bread are 0.1-0.5% (flour basis). The sulfate ions also contribute to a slightly acidic pH, which activates endogenous grain proteases and strengthens the gluten network.
2. Physical and chemical properties (list form)
• Appearance — White or off-white crystalline powder or granules.
• Odor — Odorless.
• Molecular weight — 132.14 g/mol.
• Melting point — Decomposes at 235-280°C (does not truly melt; decomposes to ammonia and ammonium bisulfate).
• Solubility in water — 70.6 g/100 mL at 0°C; 103.8 g/100 mL at 100°C (highly soluble).
• Solubility in other solvents — Insoluble in ethanol, acetone, and organic solvents.
• pH (5% aqueous solution) — 5.0-6.0 (slightly acidic).
• Density — 1.77 g/cm³ at 20°C.
• Hygroscopicity — Slightly hygroscopic; may cake in humid air.
• Stability — Stable under normal storage; decomposes when heated above 250°C releasing ammonia and sulfur oxides.
3. Food applications and usage levels (list form)
• Bread and bakery products — 0.1-0.5% (flour basis) as yeast nutrient and dough conditioner; improves volume and crumb structure.
• Caramel color production (Class III – ammonium caramel) — Used as a reactant in the caramelization process with ammonium compounds to produce a dark brown color with positive colloidal charge.
• Vegetable firming (pickles, canned vegetables) — 0.02-0.05% as a firming agent (less common than calcium salts).
• Wine and cider making — 0.02-0.1% as a yeast nutrient in stuck fermentations.
• Cheese starter cultures — Sometimes added to culture media as a nitrogen source.
4. Regulatory status and safety (paragraph form)
Ammonium sulfate is classified as GRAS by the FDA under 21 CFR 184.1143 (affirmed as a direct food additive for baking and cheese). The acceptable daily intake (ADI) is "not specified" by JECFA, indicating no safety concerns at typical usage levels. When consumed, ammonium sulfate dissociates in the stomach; ammonium ions are converted to urea in the liver via the urea cycle, and sulfate ions are excreted in urine or used in detoxification pathways. At very high doses (above 5 g per day), ammonium sulfate can cause gastrointestinal irritation, nausea, and diarrhea due to osmotic effects. Individuals with liver disease or urea cycle disorders should avoid excessive intake because impaired ammonia detoxification can lead to hyperammonemia. Allergic reactions are rare. Maximum permitted levels in EU: 5 g/kg in bread (as ammonium salt limit) and 10 g/kg in caramel color production.
