Vietnamese fish sauce (nước mắm): how it’s made and how to choose it

Every table in Việt Nam has it, and almost every dish leans on it. Nước mắm, fish sauce, is the salt, the depth and the smell of Vietnamese cooking. Sniff a good bottle and it hits you hard. Cook with it, or mix it into a dipping sauce, and it mellows into something savoury, rich and round.

How it’s made

The recipe is short: anchovies (cá cơm) and salt. The fish are packed with salt and left to ferment for many months, until they break down and give up a clear, amber liquid. That liquid is fish sauce.

The most famous comes from Phú Quốc, the island off the south-west coast, where it ferments in big wooden barrels. Phan Thiết, on the coast north-east of Sài Gòn, and Cát Hải, an island near Hải Phòng in the north, are famous for theirs too.

• Nước mắm nhỉ: the first pressing, the first liquid drawn from the fish. It is the prized one, and it is priced like it.
• Nước mắm truyền thống: “traditional fish sauce”, words many traditional makers put on the label.

How to choose a bottle

• Check the degrees. Labels often show protein strength in degrees, độ đạm, usually written as a number with °N. Higher means richer and stronger, and usually pricier.
• Read the ingredients. Traditional fish sauce is anchovies and salt. Plenty of everyday bottles add water, sugar, flavour enhancers or colouring. They are fine for the table, just not the same thing.
• Look at it. Good fish sauce is clear, from amber to a deep reddish brown.
• Don’t chase the top number. For a first bottle, a traditional one in the middle of the range is plenty, especially if most of it is going into dipping sauce.

Nước chấm: the dipping sauce

Neat fish sauce goes into the pot, or into a little saucer with fresh chilli. At the table, though, you mostly meet nước chấm: fish sauce mixed with lime, sugar and water, with garlic and chilli floating on top. It comes with spring rolls, bánh cuốn, broken rice (cơm tấm) and the grilled pork of bún chả.

A common starting point is roughly 1 part fish sauce, 1 part sugar, 1 part lime juice and 3–4 parts water. For two people, that is 2 tablespoons each of fish sauce, sugar and lime, and 6–8 of water.

1. Stir the sugar into the water until it dissolves. Warm water helps.
2. Add the fish sauce and the lime juice.
3. Add a little crushed garlic and sliced fresh chilli.
4. Taste. It should be salty, sweet, sour and hot all at once, with nothing shouting. Adjust and taste again.

Every family has its own balance, and so does every region. In Hà Nội, the bún chả bowl comes warm, often with vinegar in the mix. Make it yours.

Cooking with it

• A splash goes into soups, stir-fries and marinades, where salt would go.
• The smell fades as it cooks, and the savoury depth stays.
• Vegetarian? Fish sauce hides in a lot of dishes, so ask. There is also nước mắm chay, a vegetarian version. Our vegetarian guide has more.

Taking some home

• Choose a plastic bottle: lighter, and it won’t shatter.
• Tape the cap shut, seal the bottle in two zip bags, and wrap it in clothes in the middle of your suitcase. Fish sauce leaking in a suitcase is a smell that stays for good.
• The usual carry-on liquid limits apply, so a full-size bottle goes in your checked bag.
• Some airlines restrict fish sauce, so check your airline’s rules before you fly.

Cook with it, or take it home

In Sài Gòn, our Market-to-Wok Cooking Class starts in Bến Thành’s back lanes with a market auntie, then you cook four southern dishes in her home kitchen, eat lunch together and take home printed recipe cards. To cook at home, the Street Kitchen Spice Box packs the pantry behind the stalls: Phú Quốc fish sauce, a phở spice bag for six bowls, chilli salt and rice paper, with six recipe cards from our hosts.