Ingredient

Fish sauce

Fish sauce is small fish salted and left in barrels for months until they break themselves down into a clear amber liquid. It smells startling and tastes, in a dish, of almost nothing but savouriness. It is the single most useful bottle in the cupboard for making food taste of more without tasting of fish.

What is in the bottle

Anchovies or similar small fish, and salt. Often nothing else.

The fish are layered with salt and left, and the salt does two jobs at once: it keeps out the organisms that would rot the fish, and it leaves in place the fish's own digestive enzymes, which set about breaking the flesh down from the inside. Over months the proteins are cut into amino acids and the solids collapse into liquid.

A great many of those amino acids are glutamate. That is why fish sauce reads as savoury rather than as fishy: what you are tasting is largely the same compound that makes parmesan, soy sauce, mushrooms and ripe tomatoes taste the way they do.

This is not an exotic idea. Roman garum was made the same way, and southern Italy still produces colatura di alici, which is fish sauce by another name and a very good one.

Reading a label

There is a real quality range here, and the bottle tells you more than most.

Ingredients

Anchovy and salt, and perhaps sugar, is the good end. A long list with hydrolysed protein, flavour enhancers and caramel colour is the industrial end and tastes flatter and harsher.

Nitrogen content

Many Vietnamese bottles print a degrees-N figure. It measures protein breakdown and, roughly, concentration of flavour. Higher is stronger and generally better made.

Colour

Clear reddish-amber is what you want. Very dark brown or murky usually means caramel colour or a lower grade.

First press

Language like "first extract" or "nhĩ" indicates the liquid drawn off before the barrels were topped up with brine. More concentrated, more expensive, better.

Regional style

Vietnamese nước mắm tends to be lighter and rounder; Thai nam pla saltier and sharper; Filipino patis stronger again. All are usable everywhere — it is a preference, not a rule.

How to use it

The governing fact: fish sauce is salt plus savouriness, so it replaces some of the salt rather than being added on top of it.

• In dressings and dipping sauces, with lime, sugar, chilli and garlic. This is nước chấm and its relatives, and it is the purest expression of what fish sauce does.
• In marinades, where the salt penetrates and the savouriness stays on the surface to help browning.
• In stir-fries and curries, added towards the end. Prolonged boiling drives off the aromatic top notes and leaves it flatter.
• In non-Asian food, quietly. A teaspoon in a bolognese, a stew, a tomato sauce, a gravy or a braise deepens it noticeably and does not taste of fish. This is the single most useful thing to know about the bottle.
• In place of anchovy in a dressing, a lamb dish or a puttanesca.
• Under-rather-than-over. It is potent, and a dish that has had too much cannot be walked back.
• Vegan substitutes — soy sauce with a piece of kombu, mushroom soy, or a commercial vegan fish sauce — get you the savouriness and not the specific funk.

The smell, and why it is not a warning

An open bottle smells assertive and slightly barnyard-y. In the dish, almost none of that survives. The volatile compounds that carry the smell are a very small fraction of what is in the bottle and they largely disperse; the glutamate, which has no smell at all, is what stays behind.

This is worth stating plainly because it is the reason people who "do not like fish sauce" have usually only ever smelled it. The gap between how a bottle smells and how a finished dish tastes is wider here than for any other common ingredient.

A bottle keeps for a very long time — it is essentially saturated with salt. It will darken over months in the cupboard, which dulls it somewhat; the fridge slows that down, and is worth it if you use it slowly.

Common questions