And, of course, umami explains Escoffier’s genius. The burned bits of meat in the bottom of a pan are unraveled protein, rich in L-glutamate. Dissolved in the stock, which is little more than umami water, these scraps fill our mouths with a deep sense of deliciousness, the profound taste of decay. The culture of the kitchen articulated a biological truth of the tongue long before science did because it was forced to feed us.

For the ambitious Escoffier, the tongue was a practical problem, and understanding how it worked was a necessary part of creating delicious dishes. Each dinner menu was a new experiment, a way of empirically verifying his culinary instincts. In his cookbook, he wrote down what every home cook already knew. Protein tastes good, especially when it’s been broken apart. Aged cheese isn’t just rotten milk. Bones contain flavor. But despite the abundance of experiential evidence, experimental science continued to deny umami’s reality. The deliciousness of a stock, said these haughty lab coats, was all in our imagination. The tongue couldn’t taste it.

What Ikeda needed before science would believe him was anatomical evidence that we could actually taste glutamate. Anecdotal data from cookbooks, as well as all those people who added fish sauce to their pho, Parmesan to their pasta and soy sauce to their sushi, wasn’t enough.
Finally, more than 90 years after Ikeda first distilled glutamate from seaweed, his theory was unequivocally confirmed. Molecular biologists discovered two distinct receptors on the tongue that sense only glutamate and L-amino acids. In honor of Ikeda, they were named the umami receptors. The first receptor was discovered in 2000, when a team of scientists noticed that the tongue contains a modified form of a glutamate receptor already identified in neurons in the brain (glutamate is also a neurotransmitter). The second sighting occurred in 2002, when another umami receptor was identified, this one a derivative of our sweet taste receptors.

These two separate discoveries of umami receptors on the tongue demonstrated once and for all that umami is not a figment of the hedonist’s imagination. We actually have a sense that responds only to veal stock, steak and dashi. What’s more, as Ikeda insisted, the tongue uses the taste of umami as its definition of deliciousness. Unlike the tastes of sweet, sour, bitter and salty, which are sensed relative to one another (this is why a touch of salt is always added to chocolate, and why melon is gussied up with ham), umami is sensed all by itself. It is that important.

This, of course, is perfectly logical. The tongue craves sweet things because the body requires glucose for energy. Likewise, we love the flavor of denatured protein, because, being protein and water ourselves, we need it. Our body produces more than 40 grams of glutamate a day, so we constantly crave an amino acid refill. (Species that are naturally vegetarian find the taste of umami repellent. Unfortunately for vegans, humans are omnivores.) In fact, we are disposed from birth to savor umami: breast milk has 10 times more glutamate than cow milk. The first taste we ever know is deeply umami, preparing us for a lifetime of eating cheese, seared steak and deglazed-pan sauces. The tongue loves what the body needs.

Adapted from Proust was a Neuroscientist by Jonah Lehrer. Copyright © 2007 by Jonah Lehrer. Reprinted by permission of Houghton Mifflin Company. All rights reserved.