Call it umami's revenge. Although this savory "fifth taste" — after salty, sweet, bitter, and sour—has been known for more than a century, it has only recently become a culinary juggernaut. Monosodium glutamate, the cheap and easy way to get that umami hit, was once demonized as the cause of an allergic reaction known as Chinese restaurant syndrome, but that's been debunked by scientists. Here's the story of umami, in the lab and on the plate.
In 1907, Japanese chemist Kikunae Ikeda wondered what gave seaweed broth its unmistakable flavor, a quality he called umami. He found it was glutamic acid, and when bound to a sodium ion it formed a stable, tasty compound: monosodium glutamate. Ikeda later synthesized it by treating wheat gluten with hydrochloric acid. MSG debuted in 1909 under the name Ajinomoto, and the eponymous company is now the world's largest maker of MSG.
In the 1950s, Japanese scientists found a glutamic-acid-producing bacterium in a surprising place: soil samples taken from the ground under birdcages at Tokyo's Ueno Zoo. In the lab, Corynebacterium glutamicum, as it was named, secreted a remarkable quantity of glutamate, 10 grams for every 50 grams of sugar. It's now often used as the basis for MSG production.
Today's food makers are still working with bacteria that convert glucose to glutamic acid efficiently. In 2002, Ajinomoto isolated a new species that could grow even at high temperatures. As Ajinomoto North America senior vice president Brendan Naulty explains, "the glucose is the food for the microorganism, which craps out an amino acid. You keep it nice and warm and feed it lots of air. It's a happening environment." A 200,000- liter fermenter can produce 10 metric tons of glutamic acid in one 35-hour feeding frenzy.
Drawn from the fermentation tanks, the glutamate broth is filtered or centrifuged. Add sodium, and MSG crystals precipitate out of the solution. It looks like Epsom salt and has a faint smell of peptone (think of a really clean fish market). Dissolved in warm water, it tastes like chicken broth. Ajinomoto sells MSG in 100-pound drums for food manufacturers or in little red-and-white packages for home cooks. The glutamate in manufactured MSG is chemically indistinguishable from the free glutamate present in food, and federal guidelines have established no upper limit on safe consumption; the US Food and Drug Administration permits MSG in foods labeled "natural."
We taste MSG on our tongues, but umami receptors are also doing something in our pants: They exist throughout the digestive system, all the way to the colon. When our gut "tastes" MSG, it releases endocrine hormones like cholecystokinin that affect satiety—the sensation of being full. For example, babies are satiated longer by less when glutamates are present in their formula. These taste receptors show up in sperm and testicles too, but we don't know what function they serve.
What's unique about umami is the synergy between glutamate and bits of broken-down ATP and RNA, produced when enzymes chomp up nucleotides. These fragments magnify umami—a signal that probably evolved to tell big-brained omnivores "this comes from a living creature, so it's going to have a lot of nutritional value." Cooks can unlock these elements through aging, curing, and microbial fermentation.
The mouth holds some 5,000 taste buds planted into the tongue's papillae. Each onion-shaped bud, about 40 microns wide, contains 50 to 100 modified skin cells capable of detecting sweet, sour, salty, bitter, and umami in the dissolved chemical stew we call food.
When tastants seep over a small opening on the tongue called the taste pore (1), hairlike projections (microvilli) (2) on the tip of a taste cell capture the chemical tastants. (The molecules tie up at what are known as G-protein-coupled receptors.) Eventually, nerve cells (3) deliver messages to the brain, where they are turned into electrical stimulation. Scientists theorize that specific tastes correspond with distinct neural hot spots. The umami hot spot appears to light up near salty and sweet.
The sandwich you get at LA-born Umami Burger is optimized for flavor. In almost every layer, restaurateur Adam Fleischman unleashes glutamate that will trigger your tongue to tell your brain that maximal deliciousness has been achieved. —P.A.S.
Ketchup, the Esperanto of condiments, hits sweet, sour, salty, and umami notes. This version is juiced with onion powder and the secret Umami Master Sauce.
Fleischman's recipe includes sautéed fresh shiitakes, though dried mushrooms would contain at least 10 times as much free glutamate.
These are glazed in master sauce and oven-roasted. This increases their glutamate levels, which are especially concentrated in the pulp surrounding the seeds.
Fermentation breaks down the proteins in cow's milk, creating glutamate-rich cheese.
Providing more sweet notes than savory, these onions are sautéed with star anise to caramelize them and bring out their umami flavor.
The dust contains dried shiitake powder, anchovies, and dried kombu. The sauce contains such umami-boosting ingredients as soy sauce, Marmite, and concentrated dashi broth. Dried kombu seaweed, the basis for most dashi, has one of the highest concentrations of free glutamate in the world.
Fleischman uses house-ground fresh meat, which actually doesn't have a whole lot of umami flavor, because the glutamate is locked within the protein. He makes up the difference by impregnating the patty with his glutamate-rich sauce.
A second layer of ketchup ensures there isn't a tomato sauce glut in any one spot.
Fleischman selected this particular baked good for the burger-to-bun ratio. It's also soft enough to mop up juices but hardy enough to support the weight of his tasty stack. The source is a secret, and since the levels of glutamate in bread are negligible, it doesn't deliver much, if any, umami. Not that this burger needs any more.
