When fish sauce arrived on Southeast Asian tables remains a mystery, but its invention was inevitable. In a region blessed with abundant fish but, even today, lacking refrigeration, people naturally figured out how to preserve this valued protein source.

Description
Fish sauce is a Southeast Asian staple. Completely natural, this condiment can be made with a variety of fresh and saltwater fish, but most versions rely on anchovies, which are plentiful and low in value. The whole fresh fish are packed in sea salt in wooden barrels, earthenware jars or concrete bins, and allowed to ferment for six months to a year, or even longer, before the resulting liquid is drawn off, filtered and bottled.

It has a very pungent, salty taste. For those not brought up with this ingredient, the smell may take a little getting used to but if you have eaten and enjoyed the food of Thailand and Vietnam it is certain that you have survived a close encounter with the pungent seasoning.

Nutritional Values
In addition to flavour, fish sauce provides protein and vitamin B in diets that are not traditionally rich in these nutrients, being based chiefly on rice.

Buying
There are different grades of fish sauce, the Thai version being paler and milder than the Vietnamese. Cheaper fish sauce is used in cooking, and the more expensive first yield is reserved for adding to dipping sauces. The first extraction is the highest in protein, the best flavored and the most valued, but most producers will re-cover the fish with brine to produce a weaker second or even a third extraction, analogous to re-steeping tea leaves.

Fish sauce should be the color of brewed black tea. Avoid any that are as dark as soy sauce or cola. The best ones are pleasantly fishy and not excessively salty.

Storing
It will keep indefinitely without refrigeration, storing in a cool, dark place. Replace it if it darkens.

Using
Different brands can vary considerably in salt content, so use it cautiously in any recipe that calls for it, adding a modest amount at first and then adding more to taste.

Fish sauce is commonly diluted with water and balanced with lime juice, chiles and sugar to make a Thai or Vietnamese dipping sauce, or splashed into a meat marinade or curry, where it contributes a distinctive background note.

In Vietnam, the first extraction is called nuoc mam nhi, a phrase that appears on the label, and some cooks reserve this premium product for raw uses, such as vinaigrettes, dipping sauces or final off-the-heat seasoning. For marinades or cooked dishes, they use the less expensive blends.

Any place anchovies go, fish sauce can go, too - in a vinaigrette, in a tomato sauce for pasta. Anchovy is a little more fishy. Fish sauce is more subtle, more of a caramelized flavor.