Visit any restaurant, home, street corner or shop in Vietnam and there is one thing you will be guaranteed to find: fish sauce.

Quite easily the soul of Vietnamese cuisine, nước mắm is the county’s most loved and versatile condiment.

Its pungent, salty and slightly sweet flavour is truly like no other, making it not only a southeast Asian favourite but a common ingredient now found in the West.

Use it in marinades before cooking, as a seasoning during or as a simple dipping sauce as you eat, there is nothing it can’t do.

But what exactly is fish sauce and where is it made? How can you tell the good from the bad? And what’s the best way to cook with it?

How Did it Come to Be?

Believe it or not, fish sauce dates as far back to Roman times, where a similar, fermented fishy liquid was brewed up called garum.

Created from the likes of anchovies, sardines or mackerel, garum was much like the nước mắm we can buy off the shelves today. The fish, for example, would be salted and left to ferment in the sun for several months until ready to consume.

Another good indicator of quality is to look out for a nitrogen content. Typically, this will be marked on the front of the bottle as “degrees N”, referring to the amount of nitrogen per litre.

The amount of nitrogen denotes the quantity of protein in each drop—and the higher the protein, the more concentrated the liquid is.

Industry standard is considered to be “30N”, while “40N” is seen as high quality. Anything under “30N” is seen as low-grade.

Choosing Your Fish Sauce

Fish sauce is made all over Asia, but the best is said to come from two places in Vietnam: Phu Quoc, a tropical island off the southwest coast and the southeast coastal town of Phan Thiet.

Both of these locations boast of many reasons for why their fish sauce is the best, but they mainly refer to the quality of the fish, the sea salt used and the region’s perfect climate during fermentation.

Phú Quốc-based Red Boat fish sauce is one such brand that hails its “all natural – 100 per cent pure” liquor. They even produce a “50N” fish sauce variety.

Red Boat says its “first press” sauce is made with wild black anchovies, which are salted immediately after being caught and then aged in traditional wooden barrels under the Phú Quốc sun.

Another well-known fish sauce brand is Viet Huong, which was actually set up in San Francisco by a Chinese-Vietnamese immigrant. Viet Huong is behind a number of labels, including Three Crabs and Flying Lion. Despite its American base, it has facilities in Phú Quoc as well as Thailand.

Popular Phan Thiet brands include the Lien Thanh company, which has been around since 1906.

They have a full range of products, from premium to affordable as well as a vegetarian option.

How to Store It

It’s important to note that fish sauce has a shelf life. Its high salt content acts as a preservative, which means that it can be kept at room temperature, although it may last longer if you store it in the fridge.

But be sure to discard your bottle if it begins to smell rotten or if salt crystals or mold begin to form around the opening.

Cooking With It

Of course, what good would fish sauce be without some cooking ideas?

The beauty of nước mắm is its strength of flavour. Such boldness marries wonderfully with meat in marinades and glazes.

One popular Vietnamese dish is cánh gà chiên nước mắm—fish sauce chicken wings. To make it, chicken wings are floured, fried and then flavoured with garlic, chilli, a little sugar and fish sauce.

Nước mắm is also used as a seasoning during cooking much in the same way that Westerners use salt. But, of course, fish sauce is able to give a depth of flavour to a meal that salt is unable to do.

A popular dipping sauce in Vietnam is used after cooking too, known as nước chấm. It is made with fish sauce, chilli, lime juice, vinegar and sugar. It acts as a perfect accompaniment to most meals; from spring rolls, to grilled meats or even with noodle soup.

Whoever thought that fermented fish could be so versatile and tasty?