E251: Sodium Nitrate (Chile Saltpeter / Slow Curing)

Direct Answer

E251 (Sodium Nitrate / NaNO3) is an inorganic salt serving as a slow-release chemical reservoir of nitrite in long-aged cured meats and hard cheeses. INS 251, ADI is 3.7 mg/kg bw/day, enzymatically reduced into nitrite over months of curing.

Source: EFSA / USDA FSIS · Last reviewed Aug 28, 2026

Specs

E-Number Code	E251
INS / Codex Number	INS 251
Functional Class	Preservative, Curing Agent, Antimicrobial
Acceptable Daily Intake (ADI)	3.7 mg / kg body weight per day (as nitrate ion)
Chemical Formula	NaNO3
Primary Mechanism	Micrococcus and Staphylococcus bacterial nitrate reductase slowly converts nitrate (NO3-) into bioactive nitrite (NO2-)
Common Target Foods	Prosciutto di Parma, dry-cured salamis, Gouda cheeses (prevents late blowing by Clostridium tyrobutyricum)
Dietary Compliance	Mineral synthesis, Halal, Kosher, Vegan compliance
Safety Approval	EFSA Authorized / FDA 9 CFR 424.21

Late Gas Blowing Prevention in Hard Cheeses

In cheese making from silage-fed cows, trace Clostridium tyrobutyricum spores survive pasteurization and produce butyric acid gas that splits aging wheels. E251 nitrate inhibits spore germination without halting lactic starter cultures.