Fish sauce is a condiment derived from fish that have been allowed to ferment. The term describes a wide range of products used in many different cultures at different times.
Fermentation is normally used to describe microbial digestion of carbohydrates (starches and/or sugars) necessary to produce certain foodstuffs (such as beer, bread, wine, cheese, and yoghurt). The chemical changes involved in the production of fish sauces are different in this respect, but similar from the perspective of the cook.
Some fish sauces are made from raw fish, others from dried fish, some from only a single species; others from whatever is dredged up in the net, including some shellfish; some from whole fish, others from only the blood or viscera. Some fish sauces contain only fish and salt, others add a variety of herbs and spices. Fish sauce that has been only briefly fermented has a pronounced fishy taste, while extended fermentation reduces this and gives the product a nuttier, cheesier flavor.
Fish sauce is much used in Southeast Asian cooking to add saltiness to the dishes. Asian fish sauce is made from anchovies, salt and water, and it needs to be used in moderation because it is intensely flavoured. The variety from Vietnam is generally called nước mắm, and the similar condiment from Thailand is called nam pla (น้ำปลา). In China, it is called yu lu (魚露) and in the Philippines it is called patis. The Indonesian semisolid fish paste trassi, the Cambodian prahok and the Malay fermented krill brick belacan are other popular variations of the same theme.
A similar fish sauce was ubiquitous in Classical Roman cooking, where in Latin it is known as garum or liquamen. In English it was formerly known as fishpickle. The original Worcestershire sauce was a similar product, brought to England from India.
Some have suggested anchovy paste as the modern descendant of garum, but it is not fermented.
Here is a recipe from the 1881 Household Cyclopedia for an antique non-fermented fish sauce.
Take:
Set all these over a slow fire to simmer an hour, then strain it through a sieve; when cold put it in a bottle with the spice, but not the herbs. To a large coffeecupful cold, put a pound of butter; stir it over the fire till it is as thick as cream; shake the bottle when used, and put no water to the butter.
External links
Fish Sauce - How it is Made, by Kasma Loha-unchit, a Thai cooking instructor and author living in the U.S.