Flavor

by Bob Holmes

  After many generations of breeding, Mazourek has ended up with what he thinks is the best butternut squash on the planet. Sometimes called the Barber squash—after Dan Barber, a New York City chef who encouraged his efforts and now serves the squash in his restaurant—Mazourek’s squash has more dissolved solids and a higher carotenoid content than any other squash. “Everything is amped up,” says Mazourek. Better yet, the fruits have a built-in ripeness indicator, changing color dramatically from deep green to a rich caramel brown when they’re perfectly ripe, so that pickers can be sure they spend long enough on the vine. “There’s about a fourfold boost to the carotenoid content in the Barber squash,” Mazourek says proudly. “Half of that is in the squash itself. The other half is that it’s ripe.”

  For most consumers, though, the biggest immediate payoff is likely to come from Klee and his tomatoes. Since my visit, Klee has been digging deeper into the genetics of tomato flavor. In collaboration with a research group in China, he has now fully sequenced the genomes of more than four hundred tomato varieties, and fully mapped out their chemical content. In the same way that human geneticists search the genome for gene variants, or alleles, that contribute to diseases, Klee has scoured these tomato genomes for alleles that are important for production of sugars and volatiles. And he can compare modern commercial varieties to heirlooms to see exactly where breeders went wrong.

  Back in the 1920s, breeders latched on to a chance mutation that eliminated the dark green “shoulders” on unripe tomatoes. The new, uniformly colored fruit helped growers decide the best time to harvest, and consumers preferred the solid red color in the grocery store. (“People do buy with their eyes,” says one tomato grower.) The mutant looked like a big winner—and, in fact, almost all commercial tomatoes grown today carry this mutation. But there was a downside: To allow the green shoulders to redden fully, the mutation interfered with the production of chlorophyll in the fruit. Less chlorophyll means less photosynthesis. The new tomatoes lost out on a sugar boost that green-shouldered tomatoes enjoy—and, as a result, uniformly ripening tomatoes have about 20 percent less sugar.

  For volatiles, the losses were even worse. Over the course of decades of breeding for high yield, the high-producing alleles for flavor volatiles have simply fallen by the wayside, because breeders didn’t know they were important and didn’t test for flavor. “For the volatiles, I’d say at least half of them are the wrong alleles,” says Klee. Fortunately, the good alleles are still there in the heirloom varieties—and now that Klee knows which genes are important, it should be straightforward to breed the good alleles back into higher-yielding varieties. “The road map is very clear. We know exactly what we need to do,” says Klee. “It just takes time.”

  It shouldn’t be long before everyone should have access to tastier tomatoes, and perhaps other crops as well. Even before that, though, cooks will still strive to draw as much flavor as they can from the raw materials in their kitchens.

  Chapter 8

  THE CAULIFLOWER

  BLOODY MARY AND OTHER

  CHEFLY INSPIRATIONS

  Hyde Park, New York, used to be famous as the hometown of U.S. president Franklin D. Roosevelt. To most food lovers today, it’s better known as the site of the Culinary Institute of America. The CIA, as it’s known, is America’s preeminent culinary school, the nursery that incubated countless top chefs.

  For all its august stature now, the CIA had a fairly modest beginning. As the Second World War drew to a close, America faced a flood of newly demobilized young soldiers who needed jobs—and, in many cases, needed job skills, having spent the entirety of their brief adult lives in the military. The wife of Yale University’s former president figured some of those returning soldiers could find work as cooks, so she founded the New Haven Restaurant Institute to teach them how. The idea took off, and the little cooking school soon acquired grand ambitions and a grand name to match. By 1970, the CIA had outgrown its home near the Yale campus in Connecticut, and it moved into its present location on the Hudson River, an hour upstream from Manhattan. The big brick main building was once a Jesuit novitiate, a retreat for trainee priests—a nice parallel for today’s novices as they prepare for a lifetime’s dedicated service at the stove, rather than the altar.

  Of all the CIA’s eminent instructors, the two best positioned to bridge the gap between the science of flavor and its application in the kitchen are Chef Jonathan Zearfoss and Dr. Chris Loss. Together, Zearfoss and Loss teach flavor science to the aspiring chefs. They’ve spent a lot of time pondering the science behind what tastes good, and both of them are comfortable in the lab as well as in the kitchen. I met the two over lunch at the CIA’s Italian restaurant, the Ristorante Caterina de’Medici. As we sip spritzers of grapefruit juice and mint, Zearfoss explains that much of what a chef does in designing a dish is to balance contrast and similarity of the ingredients. Foods go together, he says, either because the flavors of one echo those in another so that they blend well, or because their different flavors make one another stand out. Every chef navigates his or her own path between those two beacons. It’s trendy to serve Hendrick’s Gin with cucumber to underscore the cucumbery notes in the gin itself, for example. But Zearfoss—who says he’s more of a contrast guy—always asks for lime instead, because its angular acidity contrasts against the roundness of the gin’s cucumber notes.

  Zearfoss and Loss are their own study in contrast and similarity. Zearfoss is a large, imposing man with a shaved, bullet-shaped head, small eyes, and regulation chef’s whites, and he speaks with the authority of someone who’s used to having his way in the kitchen. Loss is small, dark, and high-strung, with curly black hair and rapid speech. He’s in a suit, but tieless. It’s hard to give firm rules for managing contrast and similarity, Loss says. Almost everyone likes contrasting textures—a bit of crunch here, some creaminess there. Good chocolate brings its own internal textural contrast, as you snap off a bite only to have it melt in your mouth; ice cream gives a comparable textural treat. Often if chefs are using an unusual ingredient or presentation, they’ll pair this novelty—a contrast, in a way, with our expectations—with other, more familiar ingredients that help settle diners’ innate neophobia. But mostly, chefs just have to trust their instincts. “Sometimes it’s hard to identify what works,” he says. “It’s easier to pick out the flaws.”

  One of their favorite lab exercises is to let students use the principles of similarity and contrast to pair wine with foods. The ideal wine for the job is sauvignon blanc. The similarity angle works because of sensory suppression and release, says Zearfoss. You take a sip of the wine and enjoy the balance of flavors. Then take a bite of green pepper. The pepper contains grassy-tasting methoxypyrazine, which makes your nose less responsive to the similar methoxypyrazine notes in the wine. As a result, the next time you sip the wine, you’ll probably notice one of its other flavors instead. The wine tastes different at each sip—a complexity that adds to its interest. Certain foods—pears, passion fruit, grapefruit, and others—will inhibit other parts of the wine’s aroma, and give different sensory experiences.

  Still, a note of caution is in order. If anyone has a stake in the science of pairing food and wine, you’d think it would be Terry Acree. Acree is a flavor chemist at Cornell University with a wide-ranging intelligence that he loves to poke into the dusty cracks among scientific disciplines. Over the past few decades, Acree has put a huge amount of effort into cataloging the flavor molecules that we encounter in our food, and he’s published extensively on the flavor chemistry of wine. Here’s what he told me about the principles that determine whether a particular food and wine go together:

  What does it mean to “go together”? My mother was an interior decorator, and when I was about five, I walked in and said to my mother, “My favorite color is red.” And she said, “No it isn’t, kid. That’s the stupidest thing I ever heard of. Nobody has a favorite color. Color has a place, and you have to find out where it belongs and where it
doesn’t belong. It can only be your favorite if it’s in the right context.” So the first thing I’ve got to say about wine and food pairing is that it’s completely contextual, and almost entirely individual. It makes no sense to write a book on wine and food pairing, except to say there is such a thing as wine and food pairing, and go figure it out for yourself, because it’s your own pairing that counts.

  As I’m talking wine with Zearfoss and Loss, the servers—CIA students getting some front-of-house practice, and clearly a bit nervous with the chef and professor at the table—bring our food. Zearfoss has ordered vitello tonnato, cold poached veal covered with a tuna sauce, while Loss is eating steak and fries. Loss pushes his fries into the center of the table for everyone to share. (Too many rich, delicious meals are clearly an occupational hazard to be resisted—both men ordered with restraint and ate abstemiously.) Zearfoss eats a fry and then gestures toward his vitello tonnato. “They should have served this with french fries. It’s the perfect combination.” He points at the uniform, soft beige of his dish. “There’s no brown, there’s no crunchy, there’s nothing here with a Maillard.” In short, not enough contrast for his taste.

  The french fries come with a little crock of mayonnaise for dipping, which carries another lesson in balance. Without the mayo, the fries come across as too salty; with the mayo, they’re just right. “You don’t get the same salt impact with the mayo, because the fat coats the tongue,” says Zearfoss. “That’s the challenge of a chef. You’ve got the salt, the potato, the fat. Ultimately, what you’re trying to get in the customer’s mouth is a combination.”

  Every creative chef approaches the challenge of balancing the flavors in a dish in his or her own way. Many think in terms of base notes, middle notes, and top notes, just like industrial flavorists do. A French onion soup, for example, might have base notes of the oniony flavors, middle notes of caramelized sugars from long cooking of the onions, and a top note of sherry vinegar to make the whole dish sing. Other chefs free-associate from one flavor to the next, building the finished dish in their imagination until it’s just right. There aren’t many common threads here, as a perusal of any collection of famous-chef cookbooks demonstrates clearly.

  Where we can find commonalities, though, is in the chemistry of cooking. In a sense, a cook’s job is to collect and curate the right set of flavor molecules.

  The first way cooks can intensify flavor is by extracting and concentrating aromatic molecules to deliver a more intense hit of flavor. Extraction is all about solubility: most flavor volatiles, such as the terpenes responsible for rosemary’s piney quality, are more soluble in oil than in water. As a result, if you toss a handful of rosemary into a stew, relatively few of the terpenes will end up in the liquid; instead, they vaporize into the air, making your kitchen smell delicious but doing nothing for the stew itself. Better to fry the rosemary in butter or oil first, along with onions and garlic, so that the terpenes extract into the oil and stay in the dish. Or buzz the herb in a blender with a little oil, then strain out the leafy bits, for an intensely flavored rosemary oil to drizzle over the stew at the table.

  On the other hand, sometimes you want to minimize extraction to keep as much flavor as possible in the food itself—especially if you’re going to discard the cooking liquid. Some of the key flavor molecules in asparagus, for example, are water soluble, so if you boil asparagus, they extract into the water and end up down the sink. Sauteeing the asparagus in butter or oil minimizes this loss and keeps more of the flavor in the vegetable. For the same reason, broccoli and beans—whose key odorants are oil soluble—retain their flavor better if steamed or boiled.

  In high-end professional kitchens, chefs can concentrate flavor molecules extracted from herbs, spices, or almost anything else—including soil, seawater, and vegetation—using sophisticated (and expensive) distillation apparatus. Most of us lack the machinery to do that, but anyone can concentrate flavors via simple evaporation—for example, when we cook down a wine sauce to a syrupy consistency. Even the trainee chefs at the CIA quickly learn to have a cauldron of stock slowly reducing on the back of the stove. The process inevitably loses some of the flavor to the air, as a quick sniff will verify, but the reduced stock still packs a more intense flavor.

  The second way cooks develop flavor in the kitchen is through cooking itself—the application of heat. The transformations that heat performs on flavor are largely a matter of breaking down big molecules such as fats and proteins into smaller, more volatile ones. This is most obvious with meat, so we’ll take that as an example. In the raw state, most meats have relatively little flavor. Anyone who’s eaten steak tartare or sushi knows how subtle, almost minimalist, the flavors are. In fact, you probably wouldn’t be able to tell much difference between cubes of raw beef, lamb, and pork. All have a mild flavor that’s often described as “bloodlike,” and a slight tang of iron. The vegetable world is diverse: sometimes we eat flower buds, sometimes leaves, sometimes roots, and sometimes fruits, and they carry a wide range of volatile molecules as attractants and as chemical defenses against marauding herbivores. By contrast, most of what we call “meat” is the muscle tissue of mammals or birds, and every one of those muscles is doing roughly the same thing with roughly the same set of biochemical tools. That’s why beef and lamb taste more like each other than beets and broccoli do.

  The difference between one meat and the next is mostly a matter of the fat molecules they contain, with beef containing larger, less branched fat molecules and lamb, pork, and chicken increasingly more of the shorter, branched molecules. These fats—to be more precise, we should call them fatty acids—differ mildly in flavor on their own, but they break down into much different flavor molecules during aging and cooking. The fat that makes the most difference here, incidentally, isn’t the visible fat tissue on and between muscle fibers, the stuff you trim off if you’re meticulous about counting calories. Instead, most of the distinctive flavor of lamb, beef, and pork comes from the fat molecules known as phospholipids, which make up the membranes that enclose each cell. Researchers in England demonstrated this more than three decades ago by grinding up some lean beef, freeze-drying it, and extracting every last bit of intramuscular fat with petroleum solvent. After removing any traces of the solvent, they rehydrated the meat and cooked up the patties, boiling them in plastic bags for greater standardization. The aroma of the burgers—surprisingly, after all this chemistry—was indistinguishable from ordinary beef. The missing fat just didn’t matter. When they used chloroform and methanol to extract even the phospholipids, the resulting burgers had much less of the meaty aroma. So if you’re a carnivore, thank the cell membranes for the meaty flavor of your next stew or steak.

  This mix of fats differs subtly depending on which part of the animal the meat comes from, the breed of animal involved, and diet. Grain-fed beef, for example, has more monounsaturated fatty acids, including the very tasty oleic acid. Animals that eat a pasture diet, by contrast, end up with more polyunsaturated fats, plus a few additional flavor compounds such as skatole, a molecule that adds a pleasant funk at the concentration it’s found at in meat, but which smells fecal at higher concentrations. But because cattle and sheep are ruminants—that is, they have complex stomachs where microbes break down their grassy diet, including the fats—the flavor of their meat doesn’t depend strongly on diet. In contrast, pigs and chickens have simple stomachs and the fats in their diets more often make it into the meat intact. That’s why you’ll see specialty pork producers proudly touting animals finished on chestnuts or acorns—like the prized jamón ibérico of Spain—but rarely see specialized diets used as a selling point for beef.

  Most of the flavor of meat develops when we start to cook it, as the heat of cooking begins to break down fatty acids into smaller molecules, many of which carry strong flavors. (Dry aging of meat also breaks down fatty acids, so aged meat develops even more of these flavors.) The weak point in a fatty acid molecule is the carbon-carbon double bonds, the �
��unsaturated” parts of the molecule, so polyunsaturated fatty acids have more weak points, and break into smaller molecules, than monounsaturated or saturated fats do. These fatty acid degradation products account for most of the meaty aromas and flavors in cooked meat. They’re most obvious in meat that’s cooked at relatively low temperatures, such as by simmering or stewing. At higher temperatures, when meat begins to brown, another process dominates the flavor picture.

  The browning reaction—more formally known as the Maillard reaction after the early-twentieth-century French chemist who first described it—is responsible for a whole host of flavor changes that happen when foods cook. It’s the reason why bread is much tastier after it’s baked, why we roast our coffee beans, and why cauliflower roasted in the oven is more delicious than plain boiled cauliflower. It’s the reason we grill our steaks instead of poaching them, and why the best stews start by browning the meat in a little fat.

  Even though it’s called the Maillard reaction, what we’re really dealing with here is a vast network of interconnecting chemical reactions, almost like a braided streambed. At the upstream end, the reaction begins when amino acids and sugars react with each other to form a series of unstable intermediate compounds. Those intermediates then react with one another, and sometimes with fatty acids and other molecules in the vicinity as the process quickly becomes too complex to keep track of fully. These products give the characteristic brown color, and many of them are also volatile flavor molecules. Each food has its own unique starting point into the stream as a result of its particular mix of amino acids and sugars, so the reaction proceeds differently. That’s why roast beef smells different from baking bread.