The distinct, and pungent, substance can be used as a marinade, a stock base, a flavor enhancer or diluted to create a dipping sauce, and is a major industry in the beach towns of Phan Thiet and Mui Ne, where its production is taken as seriously as vinters take their winemaking.

The quality ranges from simple kitchen standard to high-end connoisseur specialities, depending on when in the fermentation process the liquid is drawn off.

Prices, however, do not vary much, starting at about VND10,000 (US$0.56) and going up to VND20,000. But competition between producers is fierce, with the Sao Vang Dat Viet, or Gold Star, award given to the finest product.

While there is no official tour of the factories, the first stop for curious gourmands is often Phan Thiet's Fish Sauce Joint Stock Company (FISACO), the biggest operation of all, producing 16 million liters of nuoc mam under four brand names a year.

The company gives a somewhat smellier take on a tasting tour, offering a guided walk through the processing compound and the opportunity to sample some of the end products. A stomach strong enough to tolerate the stench is an advantage.

"Anchovies or salmon are best, but you can use pretty much any fish. We collect ours from the port or market as soon as the fishermen dock every morning," said company guide Van Nhi, as he meandered between jars and barrels.

Washed by the sea

The factory makes the fish sauce in two ways. The traditional method entails covering fresh fish with salt and then placing it in earthen jars that are then left out in the sun to basically rot for up to three months.

And then there's the quicker option of replacing the jars with huge, cylindrical wooden tanks, where the liquid that comes out is placed back into the mixture at regular intervals, and then the first sauce is ready to be decanted five days later.

"We don't wash the fish first. They have already been washed by the sea," Nhi added.

At FISACO, visitors can try a selection of sauces, much like at a wine-tasting, and also purchase bottles.

For a more rustic experience, visit almost any house in Phan Thiet and Mui Ne, where yards are more often than not filled with brown earthen jars containing the olfactory-challenging fish mixture and where the air seems to shimmer more from the stench than the midday heat.

"It's very important to keep the temperature constantly high for the first few months," explained Nhu Nguyen, whose family runs a small fish sauce factory in Mui Ne.

"A higher temperature means better fish sauce. Then after a few months, you draw it off and filter it."

Once the first, high-grade sauce has been decanted, manufacturers will add more salt and water to produce a lower grade product, but like olive oil, the first collection is the best quality, and this "black gold" earns around $2 a liter.

Source: Reuters