Fish sauce are made with anchovies, mackerel, scabbard fish and salt. The bigger the fish, the more mercury you might expect, especially if predator fish like scabbard fish. They do not have any additives like sugar, hydrolyzed protein, or preservatives. Vietnamese prefer sauces without a strong smell, and transparent with a deep golden amber color. "First press" fish sauce, meaning the sauce is bottled from the first time the fermenting barrels are drained, also indicates quality. Lastly, when measuring the nitrogen level of fish sauces (N), most fish sauce on the market falls within the mid 20N range. Anything over 30N is
Fish sauce considered high-grade, and 40N is optimal. "Nước chấm" is a Vietnamese prepared fish-based condiment (also referred to as a "sauce") that is savory, lightly sweet and salty tasting, and can be sour and spicy if lime and chili peppers are added. The main components are fish sauce, water, and sugar. "Nước mắm" is made much like fish sauce, except that it is not fermented as long, and the fish is kept along with its liquid extract, not just the extract. "Mắm" can be used as a base condiment in dipping sauces with additional ingredients or used in soups or stir-fries.