Published July 1, 2004. From Cook's Illustrated.
The lighter the sauce, the lighter the flavor.
As soon as we opened the first bottle of fish sauce, the rest of the kitchen staff were off, scattering to the far corners of the building. Why the histrionics? Fish sauce is a very potent Asian condiment made of the liquid from salted, fermented fish—and smells as such. Fish sauce has a very concentrated flavor and, like anchovy paste, when used in appropriately small amounts, lends foods a salty complexity that is impossible to replicate.
We gathered six brands of fish sauce—one from Vietnam (where fish sauce is known as nuoc nam), one from Phillipines (patis), and the rest from Thailand (nam pla)—from our local supermarket, natural foods store, and Asian market. Tasters had the option of tasting the fish sauce straight up (which few could stomach) or in a modified version of the dipping sauce that accompanies our recipe for Thai-Style Grilled Chicken.
Differences in the sauces were noted immediately. Color correlated with flavor; the lighter the sauce, the lighter the flavor. Tasters had preferences, but those preferences varied greatly from taster to taster. In the end, all of the sauces were recommended. In fact, only one point (out of a total of 10) separated all six sauces.
With such a limited ingredient list—most of the brands contained some combination of fish extract, water, salt, and sugar--the differences between the sauces were minimal. And because fish sauce is used in such small amounts, minute flavor differences get lost among the other flavors of a dish. If you are a fan of fish sauce and use it often, you might want to make a special trip to an Asian market to buy a rich, dark sauce that is suitably pungent. But for most applications, we found that the differences were negligible. Because most supermarkets don't carry a wide selection of fish sauce, we recommend buying whatever is available (that will mostly likely be an Americanized brand and only lightly colored and flavored).