Fish sauce is a liquid seasoning produced by fermenting small fish (typically anchovies) packed in salt for 12–24 months, then pressing and filtering the resulting liquid. It is the primary salting agent of Southeast Asian cuisine and a secondary umami component across Vietnamese, Thai, Cambodian, Lao, and Burmese cooking.
Production
Anchovies (or small saltwater fish) are layered with salt at a 3:1 ratio by weight in large clay jars and left to ferment. The fish proteins break down via autolytic enzymes into amino acids — the same process that produces the glutamate content responsible for the sauce’s umami intensity. The liquid is drawn off, filtered, and bottled. First-press liquid is premium; later presses diluted with salt water are lower grade.
Grading
Premium fish sauce is rated by nitrogen content, measured as degrees (°N). Higher degree = more amino acid content = more complex flavour at lower volume. Thai Tiparos and Squid brand are mid-grade (~30°N); premium Vietnamese fish sauce (such as Phú Quốc island product) reaches 40–60°N and is used straight as a table condiment.
Vietnamese vs Thai vs Filipino
Vietnamese (nước mắm): typically lighter amber colour; lighter, cleaner flavour; the Phú Quốc and Phan Thiết varieties are considered the finest; used heavily in dipping sauces and marinades.
Thai (nam pla): slightly darker; more pungent aroma; used as a cooking sauce in stir-fries and soups. Brand differences are significant — Tiparos has a sharper, more fermented profile than Megachef.
Filipino (patis): similar to Vietnamese; golden yellow; used directly at the table.
Using fish sauce
Fish sauce is a replacement and amplifier for salt: it adds saltiness and umami simultaneously. A general substitution: replace 1 teaspoon regular salt with 1.5 teaspoons fish sauce (fish sauce is less concentrated by volume).
Fish sauce changes character when cooked at high heat — raw fish sauce has a sharp, pungent aroma that mellows to a savoury background note when cooked. Raw fish sauce used as a dipping sauce component (as in nuoc cham) should be balanced with lime juice and sugar to soften the intensity.
Substitute for fish sauce: soy sauce (similar function but different flavour profile); miso dissolved in water; Worcestershire sauce at half quantity.