(CNN) — Fish sauce - nước mắm, or literally 'salted fish water' - is a Vietnamese culinary icon, an indispensable national ingredient up there with olive oil or soy sauce.
But it's fair to say that the production process isn't the most fragrant, thanks to the pungent funk emanating from anchovies fermenting in vast wooden vats for a year.
However, it doesn't stop thousands of visitors a year heading to the fish sauce producer Phung Hung on Phú Quốc island, a 45-minute flight southwest of Ho Chi Minh City.
They have been in business since 1950 and are proud of their reputation as one of the leading producers on an island which many Vietnamese feel is responsible for the finest fish sauce in the country.
On the hunt for umami
The resort and its main restaurant Tempus Fugit were designed by celebrated American architect Bill Bensley.
The extensive repertoire of beautifully executed Vietnamese dishes they serve, such as seafood and pomelo salad or lobster with wok-fried greens, is largely underpinned by the unique flavor profile and prominent umami -- the "fifth taste," or unique savoriness -- as offered by Phú Quốc fish sauce.
But you don't need to look far for a taste of Vietnamese fish sauce. It's present in pho, spring rolls, com tam, banh xeo, com thit nuong and dozens of other ubiquitous dishes.
A Phung Hung employee guides visitors through the factory.
How the magic happens
The crucial ingredients in fish sauce are cá cơm (black anchovies) and smaller white anchovies. Together, they comprise about 95% of the fish used. Larger fish like sardines and herring make up the rest.
Traditionally, fish would be caught in the Andaman Sea around Phú Quốc, but today they tend to come from Tho Cho Island, around 70 miles away. They are only caught between April and September, corresponding broadly with rainy season.
Phung Hung have their own fishing boats, which allows them to oversee the whole production process. When the fish are caught, they are immediately drained while still on the boat, then salted and stored, meaning that the fermentation process has already begun, using the freshest possible catch.
They use salt that comes from the southern coastal province of Ba Ria-Vung Tau and add it in a ratio of one part to four parts fish.
When the fishing boats land, Phung Hung employees collect the 200 kilogram (440 pound) containers of fish and mix them together in their own barrels.
Fish sauce barrels used to be hand-crafted from wood of boi loi, a tree from Phú Quốc National Park, but it is now so endangered that wood has to be imported from Cambodia. Some have likened the importance of the wood to wine aging in oak barrels, imparting its own unique flavor profiles.
The hefty barrels are made from 54 slats of wood, bound together by hand with a rattan twine. It takes two men three weeks to make one.
Once the barrel is filled, workers clamber up the outside, don white gumboots and start compacting and pressing it down by stepping on the mix.
Thereafter, every day for a whole year, the liquid that seeps from the fish is drained and then returned into the vat -- but, critically, there's no stirring or mixing involved, as happens in fish sauce production in other provinces of Vietnam.
Workers monitor the contents, tasting the sauce to decide when a batch is ready.
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Part of the secret in the sauce is Phú Quốc's unique combination of environmental factors, including the right humidity and heat that slowly lets the mixture reduce down, to leave between three and four thousand liters of fish sauce per barrel.
The final stage comes when they send a sample of the sauce to the lab to get a grade of the intensity, measured in degrees of nitrogen, a byproduct of the fermentation process. Without the correct level, it cannot be certified on the bottle's label.
The mildest version starts from 35° N, while the most intense are around 45° N.
Phú Quốc fish sauces -- there are more than 70 different producers on the island -- tend to have higher degrees of nitrogen content, resulting in complex and different flavor profiles.
The first press
If you're after the most prized and expensive fish sauce, it is drawn directly from the first press of a single vat, undiluted and unmixed.
Look for the words "nước mắm nhi" on the label. That means it has come from the barrel's first extraction of liquid. Some call it "extra-virgin fish sauce."
Spanish chef Bruno Anon leads the culinary program at Regent Resort Phú Quốc and is something of a fish sauce devotee.
"Fish sauce is the national soul, the national essence of the Vietnamese people, which sets the country's cuisine apart from the rest of the world," says Anon. "In every Vietnamese meal, a small bowl takes pride of place, a sauce that ties together everything on the table."
He explains that here are multiple layers to the taste.
"It would be too simple to say that fish sauce tastes fishy, or even salty. Quality blends have a briny, rounded taste that you can even sample straight from the bottle. Your mind might go to the taste of fresh fish, or to sitting on the beach.
"Fish sauce sometimes has a touch of sweetness, a mineral flavor, or a note of caramel."
Indeed, acclaimed fine dining restaurants such as Toyo in Manila -- Filipinos are also huge fans of fish sauce, locally called patis -- and Anan in Ho Chi Minh City use fish sauce to brilliant effect in sweet dishes. Added to chocolate and ice cream respectively, they make for an utterly delicious salted-caramel feel. Back in 2016 in the Vietnamese capital of Hanoi, Anthony Bourdain took then-US President Obama for a humble bowl of bun cha, rice vermicelli with grilled pork. The key flavor profile was, as Bourdain explained it, "nước mắm -- the ubiquitous Vietnamese fermented fish sauce."
"This is killer."