Umami Burger has been causing a stir in Southern California since its inception in 2009 because its burgers are made from freshly ground beef, soft buns, and something extra: umami, or “the fifth taste.” In fact, just a little more than a year after the concept was launched, GQ named it Burger of the Year.

To understand Umami Burger, one has to understand umami. Adam Fleischman, founder and CEO of Umami Burger, says taste has traditionally been defined as being made up of four basic tastes: sweet, sour, salty, and bitter. However, he says umami provides a fifth primary taste distinct from the others, something he discovered early in his career.

“I had been in the wine business,” he says. “I was interested in the science of flavor and that was my starting point. I came up with the recipes myself, learning about umami as I went.”

Umami, which was discovered in Japan in the early 20th century, is a pleasant savory taste imparted by the amino acid glutamate and ribonucleotides, which occur naturally in some foods, according to the Umami Information Center. The center’s website states that umami “blends well” with other tastes and “rounds out flavors.”

Fleischman won’t reveal exactly what it is that gives each of his burgers umami. He says beef alone is an umami-rich food, and that he uses other high-umami ingredients in his creations. That includes truffles, anchovies, tomatoes, soy, Parmesan, and shiitake mushrooms.

The cheese for topping Umami burgers is processed in house. This, Fleischman says, increases the umami, and helps to control the melting quality of the cheese. He also developed seasonings and sauces, including homemade ketchup with umami, to boost the taste experience even further.

The foundation of his menu is the $11 Umami Burger, consisting of hand-ground beef, shiitake mushrooms, caramelized onions, roasted tomato, parmesan crisp, and homemade ketchup. The Manly Burger, another menu staple priced at $11, is beef with beer-cheddar cheese, smoked-salt onion strings, and bacon lardons. A Port and Stilton burger is topped with blue cheese and port-caramelized onions, while the $12 Truffle Burger has house-made truffle cheese and truffle glaze.

All Umami burgers are served on a soft, lightly toasted Portuguese bun that is branded with the restaurant’s logo. The bun is soft and light to soak up the juices of burgers, which are served medium-rare to accentuate their freshness.

“We grind our own meat because freshness is a priority,” Fleischman says.

While Umami Burger is a full-service concept that Fleischman calls “fine-dining fast food,” it will soon be taking the fifth taste to the masses with a quick-serve prototype. The first Umami Ko unit opens in Los Angeles’ Westwood neighborhood early this year, and Fleischman says he wants to open about 150 Umami Ko, or U-ko, units around the world.

“A quick-serve option is something our customers have asked for,” Fleischman says. “There is a segment of the consumer population that is more price conscious but still wants a menu based on quality.”

The quick-serve prototype will incorporate a proprietary electronic ordering and payment system.

“There won’t be a counter,” Fleischman says. “Guests will sit down at a table and order via touch-screen tablets and pay through the tablets as well. U-ko staff will bring the order to the table.”

All U-ko restaurants will be built from sustainable and recycled materials, as well.

Fleischman says 80 percent of the existing Umami Burger menu will be available at U-ko, including popular sides like thin fries, cheesy tater tots, sweet potato fries, and tempura onion rings. Sauces will be homemade and burgers will be served on the same soft bakery buns. Unlike the full-service locations, alcohol will not be served.

“We are also creating a new burger for it, something a little less exotic,” Fleischman says.

He says Umami Ko will have a slightly lower check average than Umami Burger. A visit to Umami Burger costs a diner between $15 and $20. At Umami Ko, the goal is for check averages to be about $10.

Each Umami Ko will be 1,000–3,000 square feet, depending on location. The first will be 1,500 square feet with 42 seats.

Fleischman says that once the concept expands beyond the L.A. market—where fans like Ashton Kutcher and Jay Leno sing the praises of Umami Burger—some explanation of umami may be needed.

“We explain umami to new customers,” he says. “The ones in L.A. tend to understand, but even in San Francisco … not so much.”

Up to this point, Umami Burger has relied on word of mouth and enormous media attention instead of paid marketing to drive sales. No advertising campaign was needed, for example, when Fleischman began offering a $100 burger made of hand-ground, dry-aged, grass-fed Wagyu beef; Grade-A Hudson Valley foie gras; freshly shaved Italian white truffles; onion marmalade; and a ’77 vintage port reduction.

“It’s not on the menu,” he says. “It’s something we do for parties. But people are calling for it day and night.”