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If Americans think at all of raw, decomposing fish, they think mostly of ways to eradicate the smell of it. They don’t think about ways to incorporate its liquids into their foods, which is exactly what Vietnamese chefs do on a daily basis. Raw fish sauce, a pungent liquid extracted from fermenting fresh fish, salt, and water, “smells like low tide to most Americans,” suggests Michael Pardus, a professor who specializes in Asian cooking at the Culinary Institute of America.

And yet Vietnamese food, with its liberal use of raw fish sauce, continues its journey into the American mainstream. A 2004 National Restaurant Association poll found U.S. consumers to be far more aware—8 percentage points more aware—of Vietnamese cuisine than they were in 1994. Thi Quach opened Viet Bistro in 2001, right in the heart of that upswing, and now non-Vietnamese diners make up 25 percent of his customer base at his restaurant in Eden Center, that Little Saigon in Falls Church. If Americans are at all repelled by raw fish products, they have a funny way of showing it.

Regardless of whether Vietnamese restaurants in the United States literally try to sugarcoat things when preparing fish sauces for American palates—some chefs say no, some say yes—one point should not be overlooked: Raw fish sauce’s main function isn’t to slap our tongues with the taste of cold, rotten anchovies. Its role is more subtle. It’s more akin to seasonings—and to Japanese seaweed.

Just how common is this mysterious ingredient on the Vietnamese menu? Executive Chef Hoa Lai includes fish sauce in his sweet-and-sour soup at Huong Que. Chef Huong Son at Huong Viet uses it as part of a grilled-pork marinade. Chef Dune K. Huynh at Nam’s of Bethesda uses it in a spicy dressing for her ginger salad. All Vietnamese chefs mix it with a variety of ingredients to make nuoc mam, sometimes known as nuoc cham, a sort of mother sauce that accompanies a wide variety of dishes. “For all practical purposes, it’s ubiquitous,” Pardus says.

Part of the secret to fish sauce is salt, which, as even a decent home cook could tell you, helps to enhance and blend flavors. Raw fish sauce includes jaw-clenching amounts of salt—the Three Crabs brand, for example, boasts 1,420 milligrams per tablespoon—as a result of its lengthy fermentation process. It makes sense, then, that bottles of premium-grade fish sauce, called nuoc mam nhi in Vietnam, serve as de-facto salt shakers at Vietnamese restaurants, seasoning phos or combining with other tabletop ingredients to make instant sauces.

But the real mystery to raw fish sauce is a different sort of salt: glutamate, a sodium salt of glutamic acid, which occurs naturally during fermentation of the liquid. Glutamic acid is the magic substance of Japanese seaweed; it’s the chemical responsible for umami, the controversial fifth taste that enhances all other flavors. Some restaurateurs seem to understand this process intuitively, if not chemically. “Without fish sauce,” says Quach, “there would be no flavor.”

Glutamate goes a long way toward explaining the ubiquity of nuoc mam, a multi-ingredient condiment that’s served with grilled meats, salads, fried spring rolls, and other items. Even though most folks generally refer to nuoc mam as “fish sauce,” chefs don’t offer the condiment so you can drown your food in fishiness but rather to enhance and complement all the other ingredients lucky enough to share a mouth with the sauce.

Nuoc mam is all about balance. Chefs try to deliver equal amounts of sweetness and saltiness, while working to cut the pungency of the raw fish sauce, so that the ingredient performs its umami function without making you think of the Fulton Street Market. Even a simple nuoc mam recipe can transform a dish. The light, Grand Marniercolored nuoc mam at Vietnam Georgetown smacks of little more than sugar and the slightest hint of fish sauce, a not unpleasant combination when tasted straight. But when paired with the restaurant’s fried shrimp toast, prepared on slices of a crunchy French baguette, the condiment not only softens the bread but also punches up the shrimp’s nutty, slightly sweet flavors.

The titular ingredient of Huynh’s ginger salad is found not among the lettuce, tomatoes, carrots, cucumbers, cilantro, and fried scallions but in the chef’s nuoc mam, which lightly coats the salad. “With ginger in (the sauce), you can’t smell the fish,” she says. The condiment transforms a rather ho-hum presentation of vegetables and herbs into something exotic, simultaneously playing up the cool, tart, and fragrant qualities of the ingredients while igniting a fire underneath them.

If you really want to experience the alchemy of nuoc mam, however, you should meet Nghia Trieu at Huong Viet. The waiter and front-of-the-house man will fix you up with an order of fried spring rolls and give you a personal demonstration on how to take a sliced roll, wrap it in lettuce with cilantro, mint, and julienne carrots, and dunk it into chef Son’s chili-paste-infused sauce. Your first bite will be a lesson in the power of nuoc mam. The flavors and textures shoot past your taste buds so swiftly you can barely catalog them: The pronounced crunch of fried rice paper gives way to the hot, vinegary fish sauce, which yields to the cool mint and fresh cilantro, which fades into a pleasing sensation of faintly sweet pork.

Once the moment passes, you’ll want to make sure what just happened was real. So take another bite of the wrapped spring roll, but this time without nuoc mam. It’s like the flavors have been drained from the appetizer. —Tim Carman

Eatery tips? Food pursuits? Send suggestions to hungry@washcp.com. Or call (202) 332-2100, x322.