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2000s Archive

The Corrections

Originally Published July 2008
Recent discoveries show us that practically everything we think we know about the science of taste is wrong, wrong, wrong.

Some revolutions are waged in blood. Others, in tomato juice. In a nameless conference room, in a faceless industrial park, off a lifeless exit on the New Jersey Turnpike, I am staring at four Dixie cups. One contains V8 juice (an eight-ounce serving of which has 480 milligrams of sodium, or 21 percent of the recommended daily allowance), one contains low-sodium V8 (in which almost a doubling of potassium chloride has cut the amount of sodium by more than two thirds), and the others contain low-sodium V8 mixed with different amounts of a concoction called Betra, which is designed to block the unpleasant aftertaste of potassium chloride.

This stretch of New Jersey is referred to as the Flavor Corridor, because many of the leading manufacturers in the multi-billion-dollar-a-year global flavor and fragrance industry have offices here, including Swiss giant Givaudan ($3.9 billion in sales last year) and America’s leader, IFF ($2.3 billion). Betra, though, is produced by Redpoint Bio, one of a few small companies that are threatening to overturn the artificially flavored apple cart.

The reason for this sudden shake-up: Staggering breakthroughs in scientific research, many accelerated by the decoding of the human genome in 2003, have completely rewritten our understanding of taste. “Flavor chemistry is finished,” says Cornell University’s Terry Acree, a leading flavor chemist with more than 40 years of experience. “Flavor chemistry is finding the chemical molecules that are important to aroma and taste. We spent decades doing this. But the other side of the equation is what’s been missing: how these chemicals interact with our bodies. That’s the part we’re getting to now.”

And what they’ve found is that nearly everything humans think they understand about taste is wrong. For generations, textbooks have trumpeted two universal truths about taste. Truth No. 1: There are four basic tastes—bitter, sweet, sour, and salty. Some have added a fifth basic taste, umami, from the Japanese umai, which refers to the savory, meaty taste first isolated in 1908 in Tokyo by Japanese chemist Kikunae Ikeda. Truth No. 2: Different tastes are detected on different parts of the tongue. This “taste map,” popularized by Harvard’s Edwin G. Boring in the 1940s, has been scoffed at by scientists for years. “That’s just hokum,” says Jeannine Delwiche, senior sensory and psychophysics scientist at Firmenich, another industry powerhouse. “You can taste everything everywhere.”

Recently, however, even the first truth has come into question. “There are no basic tastes,” says Michael O’Mahony, a sensory scientist at the University of California, Davis. “The notion was arbitrary, made up by a chap named Hans Henning in 1916.” The idea is misleading, O’Mahony continues. “The first question you should ask is, ‘What are basic tastes?’ Well, there are more than four types of taste receptors, so it can’t be that. There are more than four ways a chemical can react with a receptor. There are more than four types of neural codes those receptors can send to the brain. Lots of scientists felt they had to describe tastes using one of the four categories. It’s silly.”

So how do we make sense of all this?

Here’s an attempt at an answer, cobbled together from months of conversations with biochemists, geneticists, sensory specialists, and food psychologists. Though many consumers use the words flavor and taste interchangeably, scientists do not. Technically, flavor is a mixture of gustation, from the Latin gustare (“to taste”) and olfaction, from the Latin olfacere (“to smell”). One reason flavor has been so poorly understood is that taste and smell have long been considered minor senses, compared with vision and hearing. Delwiche estimates that for every 100 people studying vision, there are 10 studying audition and 1 studying taste or smell. Why? “We’re not taste-dominated creatures,” she says.

The tongue and the mouth, assisted by the nose, are considered the body’s primary defense against poison. They are designed to ensure that nutritious substances are ingested and harmful substances rejected. For this reason, says Hildegarde Heymann, another sensory scientist at UC Davis, the human body can taste faster than it can touch, see, or hear. The body can detect taste in as little as 1.5 thousandths of a second, compared with 2.4 thousandths of a second for touch, and a sluggish 1.3 hundredths of a second for hearing and vision.

In order to be tasted, a chemical must be dissolved in saliva and come in contact with tiny receptors that are grouped together in buds. These receptors, which are not just on the tongue but all over the inside of the mouth, convert the chemical into a nerve impulse, which then gets transmitted to the brain. The number of taste receptors humans have has yet to be finalized but will likely be around 40. “It will be a fixed number,” says Terry Acree of Cornell. (The number of olfaction receptors is much higher, around 300.)

The revolution in molecular biology allows scientists to identify which proteins, in which receptors, send which signals to the brain. Only 1 receptor can identify sweet, for instance, but more than 20 receptors detect tastes that are bitter. “With the sequencing of the human genome,” says Dr. Ray Salemme, Red-point Bio’s CEO, “people have begun to understand, on the molecular level, much of the machinery associated with taste. Chefs have known this instinctually for generations, but now we’re beginning to understand what’s really going on.”

“Taste is like a chair with four legs,” explains Acree. “Before, we only had one leg—flavor chemistry. Now we’re building the other three: how a chemical reacts with the receptor; how that receptor communicates with the brain; and how the brain processes that information into behavior.” Once scientists have identified the chain of messages each chemical sends to the brain, they can begin to manipulate that conversation. The chemical gustducin, for example, is part of the signaling mechanism between receptor and brain. If you remove gustducin from mice, they drink bitter liquids as if they were water. If researchers can find less-invasive ways to stop taste receptors from telling the human brain, “Hey, this food is bitter,” suddenly those Brussels sprouts go down a lot easier. As does a child’s medicine.

But these breakthroughs have uncovered challenges for food conglomerates, restaurant chefs, and home cooks alike: Each of us tastes differently. Though all humans have the same number of receptors, how the brain interprets what those receptors transmit can be radically different, even from family member to family member. Linda Bartoshuk, at Yale’s School of Medicine, and other researchers have known since the 1990s that some people are “supertasters”: They experience many tastes with more intensity—sugar is sweeter, Brussels sprouts more bitter, chiles hotter—than do “nontasters,” who can, for example, tolerate spicy foods more easily. Although there are some evolutionary advantages to such distinctions (supertasters tend to dislike plants with higher degrees of toxicity), there are also disadvantages: When thin, supertasters tend to be very thin, and when obese, they tend to be very obese. “What’s important,” says Acree, “is that you taste something differently than I do. It’s like you’re living in a pink world, and I’m living in a blue world, and we’re talking about the color of the ocean. We’ll never agree.”

But these distinctions are only the beginning. Recent studies suggest that cultures have genetic makeups as well. “When they started decoding the genome,” explains Salemme, “they began to look for differences in the sequences between different populations.” Researchers have now identified about a dozen haplotypes, or collections of persistent mutations within a particular population. Take lactose intolerance: A large percentage of people of African and Asian descent can’t produce the enzyme lactase, which breaks down sugars in milk. Lactose intolerance, however, is relatively uncommon in people of European descent, which may reflect the fact that there’s been a tradition of herding and milking in that part of the world for thousands of years. As scientists begin to home in on the biological foundation of different likes and dislikes, an even more tantalizing possibility arises: In the future, each of us will likely be able to identify our genetic predispositions to food. We might even have a food type, just as we have a blood type: I’m broccoli positive, you’re pumpernickel negative. To be sure, this does not necessarily equate to a like or dislike. As Salemme cautions, we can learn to modify our responses. “There are many things you might not like the first time you taste them, such as single-malt Scotch, but you learn to like them. A lot.” The direction, though, is clear: Soon each of us will carry around our own periodic table of what food chemicals we respond to. You’ll no longer be able to ask dinner guests merely if they eat meat; you’ll have to send them a detailed questionnaire.

But as my V8 taste test shows, all this knowledge of our bodies is beginning to affect what we’ll be putting into our bodies. Food companies are scrambling to come up with artificial additives that might improve or block particular flavors. Senomyx, a San Diego–based company, has raised more than $76 million from businesses such as Nestlé, Coca-Cola, and Campbell Soup to study how to enhance the taste of sugar or salt in packaged foods. In effect, products would trick the taste receptors into perceiving ingredients that aren’t there (or that are there in lesser concentrations), thus allowing, for example, manufacturers to slash the amount of salt in a can of chicken-noodle soup. Further benefiting them, the additive would be in such a tiny amount that it could be referenced in the “artificial flavors” category and not be specifically listed on the label.

Of the four samples of V8 I blind-test, I can easily detect the full-sodium version, and I find the low-sodium version to have a tinny, artificial taste. Of the two samples mixed with the potassium-chloride blocker, one is bland and the other is more tomatoey and savory. I have experienced the result they desired: The bitter blocker has made the juice taste more satisfying. “Many people are already upset about what they consume. Won’t this make them more upset?” I ask Salemme. “We’re not manipulating your genes,” he replies. “All we’re doing is saying, ‘You already add aspartame or saccharine to your coffee to block the bitter taste.’ There was a large component of serendipity in finding those compounds. Before, you could test maybe two hundred new compounds a year, because you were reliant on human testers—and they’re prima donnas. Now, with the genome, we can re-create that process artificially.” It takes me a moment to absorb the information. “So,” I say, “this means you can put taste molecules onto receptor molecules in the lab and see exactly how the receptor molecules respond.”

“Yes. And this way we can test a thousand times that number of new compounds,” Salemme clarifies. “It’s a sea change.”

If anything, diners may soon confront yet another level of science—make that science fiction—in their food. For years, chefs such as Ferran Adrià, at El Bulli, in Spain, and Heston Blumenthal, at The Fat Duck, near London, have mixed chemistry and biology in order to assert the primacy of flavor over form. Blumenthal, in fact, who serves beet jelly and bacon-and-egg ice cream, has a flavor manifesto on his website that is longer than this article. “Lots of chefs have said they don’t care about this stuff,” says Chris Young, a chemist who worked as a food-research manager at The Fat Duck. “They just care how the food tastes on the plate. That’s fine. But this research will eventually trickle down to every level of cooking.” So can he imagine using a taste blocker at a high-end restaurant? “Sure. Savory ice cream. Sugar is inherently necessary to get the particular texture that ice cream has. You need it to depress the freezing point and give you enough solids. But for a true savory ice cream, you’d need to use sugar but block the sweet taste.”

“So in five years,” I say, “can you imagine a situation where I tell you my flavor type on the Internet at the time I make my reservation and you design a meal just for my DNA?”

“Absolutely. When I worked at The Fat Duck, more than half of our clientele flew from someplace other than England to dine. This presented a problem. If we served rice pudding to American or English people, most would like it. If we served it to a Japanese person, it would be revolting. The goal in the restaurant world is to make each client feel like they’re the most important person in the world. If understanding your genome allows chefs to understand, in advance, your possible likes and dislikes, that would allow them to personalize the experience even more. There’s a greater chance of your saying, ‘That was one of the best meals I’ve ever had. I feel like the chef was cooking just for me.’”

And in this case, with my DNA doing the ordering and a chef-chemist doing the cooking, he’d be right. The only figure left out of this double helix? Me. My DNA may tell me I’d prefer a carob-tofu brownie, but I’ve just had a bad day. I want the double-chocolate surprise.

We are Family: The Human Genome Project

Humans are 99.9 percent identical to one another—and to the archetype mapped and sequenced by the international Human Genome Project (which had nothing to do with genetic engineering). The nucleus of each cell in our bodies (except mature red blood cells) contains the entire genome, and the genome’s DNA (composed of 3 billion chemical components) is arranged in 23 pairs of chromosomes, which, in turn, contain 20,000 to 25,000 genes. Genes only comprise about 2 percent of the genome; the rest serves other functions, including regulating the production of proteins, the molecules that perform most of the work of the cell. By isolating each taste receptor of the human genome, scientists can now begin to see how they react to every flavor known to humankind.