Fish sauce is often made from anchovies, salt, and water, and is intensely flavoured. Anchovies and salt are arranged in wooden barrels to ferment and are slowly pressed, yielding the salty, fishy liquid. The salt extracts the liquid via osmosis. Southeast Asians generally use fish sauce as a cooking sauce. However, there is a sweet and sour version of this sauce which is used more commonly as a dipping sauce (see "nước chấm"). Fish sauce in Burma is called "ngan bya yay" (ငံပြာရည်). In Cambodia, fish sauce is known as "teuk trei" (ទឹកត្រី), of which there are a variety of sauces using
Fish sauce "kecap" in Indonesia might be the precursor of ketchup. By 50–100 BC, demand for fish pastes in China had fallen drastically, with fermented bean products having become a major trade commodity. Fish sauce, however, developed massive popularity in Southeast Asia. Food scholars traditionally divide East Asia into two distinct condiment regions, separated by a bean-fish divide: Southeast Asia, mainly using fermented fish (Vietnam, Thailand, Cambodia) and Northeast Asia, using mainly fermented beans (China, Korea, Japan). Fish sauce re-entered China in the 17th and 18th centuries, brought from Vietnam and Cambodia by Chinese traders up the coast of the southern provinces