Nước Mắm: Anchovies, Salt, a Year of Waiting — and a Whole Cuisine

Ask a Vietnamese person living abroad what they miss, and somewhere on the list — usually near the top, sometimes said a little sheepishly — is the smell of nước mắm. It is not a pretty smell out of the bottle. It is sharp, salty, unmistakably of the sea. But splash a little into a hot pan, or stir it into lime, sugar, chilli and garlic, and it turns into something closer to a feeling: home, lunch, a grandmother’s kitchen.

Fish sauce isn’t an ingredient you add to Vietnamese food. It is the seasoning the rest of the food is built around — in roughly the way salt and butter are in French cooking, or soy sauce in Japanese.

What it actually is

The recipe could fit on a matchbox: fish and salt. Traditional Vietnamese nước mắm is made mostly from small anchovies (cá cơm), layered with coarse sea salt — producers commonly cite a ratio of around three parts fish to one part salt — and left to ferment for a year or more. Nobody adds a starter culture. The fish’s own enzymes break its proteins down into amino acids, while the salt keeps spoilage bacteria out. What drips from the bottom of the vessel at the end — the first draw is called nước mắm nhĩ — is the prize.

The fermenting mass is called chượp. In the old fishing villages, how a family tended its chượp — how often it was stirred, how long it sat in the sun, when it was drawn off — was a trade secret passed from parent to child.

Two capitals, two vessels

Vietnam has fish sauce towns from the north to the Gulf of Thailand — Cát Hải off Hải Phòng is the best known in the north — but two names dominate the conversation.

Phú Quốc, the island in the Gulf of Thailand, ferments its anchovies in huge wooden barrels in long, dim nhà thùng (barrel houses), usually for a minimum of twelve months. The island’s sauce is the one most often called the finest, and in 2012 the European Union registered “Phú Quốc” as a Protected Designation of Origin — the first Vietnamese geographical indication to be protected in the EU, with the certificate formally handed over in 2013. The application had been filed partly because sauces labelled “Phú Quốc” but made elsewhere had been sold on European shelves for years.

Phan Thiết, on the south-central coast, works on a much bigger scale and produces a large share of the country’s everyday fish sauce. Its traditional vessel is the clay jar — the tĩn — and nước mắm tĩn is its signature product. The town’s role in the trade has a political footnote: in 1906, scholars inspired by Phan Châu Trinh’s Duy Tân reform movement founded the Liên Thành company there, selling fish sauce to fund patriotic schools and activities. In 2019 Phan Thiết opened what was billed as Vietnam’s first fish sauce museum, full of jars, boats and models of the old fishing village.

How far back the craft goes is honestly unclear. Producers like to talk of “300 years”, and Nguyễn-dynasty records (1802–1945) show nước mắm being collected as a regional specialty and as tax in kind, which tells you how valuable it was. Comparisons with ancient Rome’s fermented fish sauces are fun — the Romans did make something similar — but they are parallels, not a family tree.

Reading the label: what “40°N” means

Walk down a Vietnamese supermarket aisle and you’ll see numbers on the bottles: 30°N, 35°N, 40°N, sometimes higher. This is độ đạm — total nitrogen, measured in grams per litre. Because that nitrogen comes mostly from the amino acids released as the fish breaks down, it works as a rough gauge of how concentrated and savoury the sauce is. One degree is one gram of nitrogen per litre.

A rule of thumb many cooks follow: the high numbers (35–40°N and up) are for dipping and finishing, where you taste the sauce directly; the more modest grades are fine for marinades, braises and soups. Higher is not automatically better — a 40°N sauce can still be harsh, and a well-made 30°N sauce can be lovely — and industrial products may be diluted and flavoured, so the ingredients list matters as much as the number.

Nước chấm: the sauce made from the sauce

Most of the fish sauce a Vietnamese family gets through isn’t drunk straight. It becomes nước chấm — the dipping sauce on every table. The basic version is fish sauce, water, sugar and lime juice, with garlic and chilli floating on top, adjusted until it is salty, sweet, sour and hot all at once. Every household believes its own proportions are the correct ones.

Regional habits show up here too. Northerners tend to keep it lighter and sharper, for bún chả or nem rán; southerners tend to make it sweeter. Central cooks reach for more chilli. Then there is the whole separate universe of mắm — thick fermented pastes like mắm tôm (shrimp) or mắm nêm (anchovy) — which is a story for another day.

The 2016 scare

Fish sauce matters enough in Vietnam that a single survey could set off a national crisis. In October 2016 a consumer-standards association, Vinastas, announced that most of the fish sauce samples it had tested contained arsenic above the permitted limit. Sales of traditional sauce dropped; some supermarkets pulled bottles from the shelves.

The problem was that the test hadn’t separated organic arsenic — which occurs naturally in fish and seafood and is considered harmless — from the toxic inorganic kind. The Ministry of Health and the Ministry of Industry and Trade said the sauces were safe, and in December 2016 Vinastas publicly apologised for its misleading conclusion. For many traditional producers the episode left a lasting lesson about how quickly trust in something so basic can wobble.

If you’re visiting

Visit a barrel house on Phú Quốc; most welcome visitors and will let you smell the chượp, which is an experience. If you buy a bottle to take home, check your airline’s rules on liquids and have the shop seal and box it properly — a bottle that cracks inside a suitcase is a smell you will not forget. And at your next Vietnamese meal, before you reach for the soy sauce, try the little bowl of nước chấm. That’s the whole country, in one spoonful.