Fish sauce in Vietnam, and the dip it turns into

Fish sauce in Vietnam is named in almost every article about the food and explained in almost none of them. It is also two different things, and the confusion between them is why visitors sometimes find it overpowering.

What is the difference between nuoc mam and nuoc cham?

Fish sauce in Vietnam comes in two forms. Nuoc mam is the bottle: fermented anchovies and salt, dark brown, and far too strong to dip anything in neat. Nuoc cham is what actually reaches your table — nuoc mam let down with water and balanced with lime, sugar, garlic and chilli.

Almost every small bowl beside a plate in Vietnam is nuoc cham rather than fish sauce. If you have tried fish sauce straight and recoiled, you have not tried the thing Vietnamese food is built on.

How is it made?

Producers layer anchovies with salt in wooden vats, roughly three parts fish to one part salt, and leave them for a year or more. They then draw the liquid off in successive pressings.

The first draw is the strongest and goes into the expensive bottles. Later pressings run weaker and cheaper, and most kitchens cook with those rather than dipping from them.

Where does the salt come from?

The coastal pans, and the ratio makes it the second ingredient by weight. The salt fields guide covers where those are, how a season works and why the fields sit idle for half the year.

What does the number on the bottle mean?

Nitrogen content in grams per litre, printed as degrees. It measures concentration rather than quality on its own: a 40-degree bottle is stronger and more expensive than a 25-degree one, not automatically better for the table.

For dipping, the mid-range is usually what you want, because it is being diluted anyway. The high-degree bottles are a gift item and a cook's ingredient.

Why does Phu Quoc come up so often?

Phu Quoc holds a protected designation of origin for nuoc mam, so sauce sold under the island's name has to be fermented there. Crews salt the anchovies on the boat within hours of the catch, which is the part that matters.

Several factories on the island run visits, and they are a genuinely interesting hour rather than a shopping trap. The smell is exactly what you are imagining.

Where will you actually meet it?

Everywhere, and mostly as nuoc cham. It arrives beside spring rolls, under rice plates, poured over bun cha, and stirred into the dressing of every salad.

Fish sauce also hides inside things that do not look like they contain fish: braised pork, stir-fried greens, soup bases and the marinade on grilled meat. The what to eat guide sets out which dishes lean on it hardest.

What if you do not eat fish?

Fish sauce is the hardest ingredient in Vietnam to avoid, and pretending otherwise does nobody any favours. Fish sauce is in dressings, marinades and soup bases, frequently in dishes with no visible animal ingredient at all.

Chay restaurants — Buddhist vegetarian kitchens, often near pagodas — replace it with a soy-based substitute and are the reliable option. The vegetarian guide covers how to ask elsewhere, and the allergy guide covers the same problem from the shellfish angle.

Is it the same as Thai fish sauce?

Not quite. Vietnamese nuoc mam is generally fermented longer, and tastes rounder and less sharply salty than Thai nam pla.

The larger difference is how it reaches the table. In Vietnam it is nearly always diluted into nuoc cham first; in Thailand the neat sauce appears more often as a condiment. Swapping one for the other in a recipe changes the dish more than the label suggests.

Should you bring a bottle home?

If you liked it, yes, and buy it in Vietnam rather than at home. A good mid-range bottle costs a fraction of what the same grade costs abroad, and the shopping guide covers what else is worth the suitcase space.

Wrap it twice. Every traveller who has not done this has a story about the flight home.