Cooked - A Natural History of Transformat Part 14

Having thus mangled my gorgeous dough, I had little hope for the finished bread. But when the third and biggest Moment of Truth arrived, twenty minutes after the loaf went into the oven, I was pleasantly surprised. I lifted the lid to find that the loaf had mostly self-corrected for its lopsidedness, and had sprung up-not spectacularly but respectably. Here was a round, puffy, fawn-colored pillow easily twice as large as the flop of dough I'd dropped in the pot only twenty minutes before.

I closed the oven door gently to make sure I didn't deflate the risen loaf while it finished baking. I needn't have worried: By now, the starches in the dough had "gelatinized"-stiffened enough to formalize the matrix of gluten, which had itself stiffened. During the early moments of baking, the cells in that matrix had ballooned under the pressure of gases expanding in the heat. At least for the first six to eight minutes of oven time, new alveoli continue to form, since the yeasts keep working until the temperature reaches a lethal 130F. During this period, provided there remain enough sugars to feed them, the rapid flush of heat inspires one last, climactic burst of fermentation.

When I took the bread out of the oven twenty-five minutes later, it smelled better than it looked, but it didn't look too bad. It had thrown no ear to speak of: My too-tentative slash had merely opened a pale scar in the crust. The crust was smoother and more tentatively colored than a Tartine loaf, but it was handsome even so, marred only slightly by these two curious blackened humps. A roasty aroma filled the kitchen. Still wearing oven mitts, I tapped on the bottom of the loaf and listened for the hollow, woody timbre indicating the bread was cooked through. It was. I held the loaf up to my cheek to feel its radiating warmth. The bread gave off a pleasing low static as it cooled.

The sense of accomplishment surprised me. I hadn't done much, after all, except mix together some flour, water, and a little sourdough starter, and then babied it for several hours. And yet-here was this substantial thing that hadn't existed before, this fragrant risen form. I might as well have pulled a rabbit out of a hat, and indeed my family, whose expectations for this latest project of mine were modest, reacted as if I had. Something from nothing: You can see why the prescientific mind (and the skeptics in Jesus's audience) might have been impressed. Bread science would eventually offer a material explanation for this apparent miracle, but even now that we have it, the fresh-baked loaf still feels like a creation ex nihilo, its from-mud-wrested form a refutation of cosmic entropy, its sheer plusness a tasty proof of the non-zero sum or, to put it in more homely terms, the free lunch.

But before I get carried away congratulating myself ... there were, let's not forget, those two unsightly black protuberances, rising like volcanic islands from the smooth, tan sea of crust. It wasn't until the loaf had cooled that I could slice it open and find out what lay beneath them: two yawning caverns of air that reached deep into the center of the loaf. Cavitation! A really bad case, too. Chubby pockets of air are part of the charm of a country loaf, but these were far too big and far too close to the surface to be charming. "The room where the baker sleeps" is what bakers call such cells-in derision.

PBF: Any professional baker would toss this loaf on the reject pile, a case of partial bread failure. But it smelled absolutely delicious, and when I tasted a slice, I was once again pleasantly surprised. The crust was thin and chewy, and the moist crumb had plenty of flavor-wheaty, sweet, and fragrant. This was not a half bad loaf of bread, I decided, especially if you ate it with your eyes closed.

I had a ways to go, certainly, but I didn't feel discouraged in the least. To the contrary: I felt determined to make another, better loaf, and soon. The final product might be no triumph, but something about the process had captivated me-the mysteries of fermentation, the sweetly sweaty smell of my sourdough culture, the feel of the dough in my hands, the suspense surrounding the climactic oven spring. But before I ventured another loaf, I decided it would probably be a good idea to spend some time in the company of someone who actually knew what he was doing. So I got in touch with Robertson and asked if I could come by the bakery, talk to him about how he had learned to bake bread, and maybe work a shift or two at his side.

Chad Robertson looks less a baker than the surfer he also is. He has a swimmer's long, sleek torso and a certain litheness about him. Chad is equally economical with his words, his movements, and his smiles. On my first visit to the bakery, I spent an hour watching him shape batards. He wore a white ap.r.o.n tied tightly around his waist; a visor over his brown hair shaded his brown eyes. The process is mesmerizing to watch but impossible to follow-to break down into discrete, comprehensible, imitable steps. All I could make out was a blur of dexterous fingers that looked as if they were swaddling an endless succession of infants at warp speed.

While he shaped loaves, we talked. I asked Chad about his starter. I had brought along mine in a Tupperware container, hoping to pick up some pointers on care and feeding-and, secretly, perhaps some good microbes as well, since I figured the bakery must be crawling with them.

"When I was starting out I was superst.i.tious about my starter," Chad told me, as he swiftly cut and weighed lumps of dough. "I would take it on vacation because I didn't trust anyone with it. Once, I took it to the movies with me, so I could feed it exactly on time. But now that I've lost the culture and had to start it over a few times, I'm more relaxed about it. I now tend to think it's less about nature than nurture." Meaning, roughly, that the requisite bugs are everywhere, but can be selected and trained by the baker to perform as he wants them to.

Chad showed me his culture, taking down from a high, warm shelf a metal bowl half filled with an animated white soup. It was wetter and warmer than mine, and smelled less sour. He told a story about the night one of his apprentices, cleaning the bakery at the end of her shift, accidentally threw out the bowl of starter.

"I cried. I thought I was finished as a baker. But then I found I was able to start a new culture that within a couple of days smelled exactly like the old one." Chad judges a starter by its aroma, which in his view should be more fruity than vinegary; in fact, he doesn't like his sourdough to be very sour at all. ("Sour is easy to achieve: Just don't feed the starter as often. But it's one dimensional.") Chad figures that by now the "right" yeasts and bacteria are all over his bakery and easy enough to capture. Though he also recently had experiences starting new cultures while in France and Mexico that soon came to smell and perform much like his culture in San Francisco. This has led him to the conclusion that the feeding schedule and the ambient temperature are the most important factors determining the character of a sourdough culture. But it could also be that by now Chad Robertson carries some really good bugs on his person. Which is why, before I left the bakery that evening, I opened my Tupperware to the Tartine air and asked him to p.r.o.nounce on the quality of my culture. Chad raised the container to his nose, sniffed, and nodded in mild approval.

Chad Robertson can name the very day that bread baking first captivated him: the spring afternoon in 1992 when his cla.s.s at the Culinary Inst.i.tute of America, in Hyde Park, New York, went on a field trip to the Berkshire Mountain Bakery in Housatonic, Ma.s.sachusetts. This was the day he met Richard Bourdon, a thirty-five-year-old "radical baker" from Quebec whose whole-grain sesame boule and soaring, s.e.xy spiel about the wonders of sourdough fermentation set Robertson on his course in life.

This was not the first right-angled turn in Chad's twenty-one-year-old life, however. Growing up in West Texas, on rectangles of sliced Oroweat bread, he had never given much thought to cooking as a career, much less baking. (His father had, like his father and grandfather before him, worked in the family business, making custom cowboy boots.) Chad recalls being "an obsessive kid, the type who would keep daily charts of the weather." As a teenager, he planned to become an architect, but when the one and only school he applied to-Rice University, in Houston-rejected him, he abruptly changed course and decided to go to culinary school. "I figured if I could cook I could always get work in a restaurant."

For Chad the two most important things that happened in culinary school were meeting his future wife and partner, Elisabeth Prueitt, a pastry chef, and going on that fateful field trip to Housatonic. Over lunch one afternoon during one of the shifts I worked at Tartine, he recounted the story while the bulk fermentation bubbled along back in the bakery.

"It was weird, because in the van on the way up there I had already decided that this was going to be it. I had this fantasy of apprenticing myself to Richard Bourdon and becoming a baker. It made no sense whatsoever; I had never met him or given much thought to bread. But I loved the idea of this underground baker out there in the middle of nowhere, working through the night in perfect solitude." A restaurant kitchen is a hectic, loud, chaotic place, and Chad had already begun to question whether it was the right place for him. A bakery is a monastery by comparison.

Bourdon and his bread lived up to expectations. "It was exactly what I had been imagining. I loved the atmosphere of his bakery, this big, old, dimly lit brick barn on the bank of a river. The whole bakery had the sweet smell of natural leaven. It was a new aroma and a new flavor for me. I had never seen bread that wasn't rectangular. And his bread was incredible. It had a contrast between crust and crumb I had never experienced before, and this moist, glistening interior. And then there was Bourdon himself, the radical baker! He had an intense, s.e.xual way of talking about fermentation, the invisible orgy of microbes he was orchestrating. He wanted to take everything to the absolute limit: the super-wet doughs, the long fermentation, the hard, dark bake. I loved the idea of this underground baker pushing his doughs just as far as they could go. He was a guru."

A few months later, I traveled to the Berkshires to meet the bread guru. Richard Bourdon is now approaching sixty, and though the pa.s.sage of time had clearly mellowed him a bit (he's relented, slightly, on the subject of white flour), the man was still possessed by a Dionysian fervor about bread, and fermentation, and wheat, which he mills himself fresh every day. Bourdon has an ungovernable mop of gray curls and an open, expressive face that appears to have been lined more by laughter than worry. He somewhat resembles Harpo Marx, and, like Harpo, can get across anything he wants solely by means of his facial expressions and dancing eyes. Unlike Harpo, however, Bourdon can also, in his faintly Frenchified English, talk a blue streak, giving him a doubly powerful presence. In fact, the man would probably be hard to take if he were not so charming and charismatic.

I filled several notebooks with Bourdon's soaring disquisitions on fermentation, a subject about which he has developed a great many theories, some of them more susceptible to scientific proof than others. A central one is that "souring" grains-fermenting them-"is not a cultural but a natural, instinctual process. We humans did not discover it. All indigenous peoples sour their grains, but so do many animals." This particular treatise took him all the way from Ghana to Greenland and then looped back around to his front yard and ended back in his bakery.

"What do you think the squirrel is doing when he buries acorns in my yard? He is not just hiding them! No, he's souring them, because if he didn't do that the nut would be indigestible. Birds? They don't just swallow seeds fresh. No! First they sprout them in their craw so the enzymes can start to free the minerals. Animals instinctively sour, sprout, ferment foods to extract the maximum nourishment from them while expending as little of their own body's energy as possible. That's the iron law of economy: Take the most you can from nature with the least amount of effort. So, instead of doing all the work of digestion ourselves, we let the bacteria do it for us." What he was describing sounded a lot like cooking.

"Now let us look at bread. It is the same principle but even more clever. It starts with the flour mill, this big stone tooth that chews the seed for us so we don't need to break our teeth on it. Then the sourdough culture breaks down the phytic acid in the flour, so the bacteria can get at those minerals. (Because bacteria want all the same things we do, food and s.e.x and babies!) But bread is the most intelligent system for processing food, because it has everything. It even makes its own pot! Put dough in a hot oven and the first thing that happens is, a crust forms to trap the steam. The loaf becomes its own pressure cooker! That's what cooks the starches."

For Bourdon, the problem with most bread is that it is essentially undercooked, and therefore more difficult to digest than it should be. This is why he favors long fermentations and unusually wet doughs. Wet dough was the norm before the mechanization of baking. Human hands can't handle dry doughs very well (even if they are easier to shape, they are much harder to mix and knead), and machines can't handle wet ones at all. But they make much better breads. Bourdon is fond of saying, "You would never cook a cup of rice in half a cup of water." Even more than flavor or beauty, Bourdon is after the perfect nourishment that only the most thorough cooking can ensure. He came out of the macrobiotic movement, and is something of a poet of human digestion. Which, he explains, begins in the mouth the moment you bite into a bread.

"This is why the acids in sourdough are so important! They make your mouth water, so the enzymes in your saliva can begin to digest the starches. That's how you can tell good bread from bad: Roll a little ball of it and put it in your mouth. What happens? Does your mouth feel dry, like you want a sip of water, or is it nice and wet?" The baker is the conductor of an intricate symphony of transformation that takes in everything from the gra.s.s seed to the millstone, the microbial fermentation to the pressure-cooking, and culminates in the salivation that a well-baked bread inspires in the mouth.

It was easy to see how a twenty-one-year-old might come away from a few hours in Richard Bourdon's presence convinced that baking bread was the most important thing you could do with your life. The work put you in direct, bodily contact with some of the deeper currents of the natural world, as well as some of the oldest traditions of human community. Bread, as something "made" by microbial action and human hands working in concert, falls somewhere between nature and culture, which in Bourdon's worldview exist not in opposition to each other but on one glorious, Rabelaisian continuum, reaching all the way from "the mindless f.u.c.king and farting" of bacteria to the sprouting of acorns by squirrels to the civilized pleasures of breaking bread at the table.

Before the group left Bourdon's bakery that afternoon, Chad summoned the nerve to ask him about an apprenticeship. So began five months of a brutal but life-altering internship, with Chad making the long drive up to Housatonic every night after cla.s.ses, working in the bakery from four until nine in the morning, and then driving back down to Hyde Park for another day of cla.s.ses. After graduation, Bourdon wanted to hire Robertson, but had no openings. So Chad worked for nothing but room and board, until a spot opened up. Chad ended up spending two years in Housatonic, absorbing Richard's pa.s.sions and methods and ways with the wet dough.

Richard recalls, "Chad was good at everything, but he had a perfectionist streak. He would bake only three loaves wide, so that each bread had plenty of personal s.p.a.ce in the oven. And if the loaves didn't spring up nice and big, he'd be upset. Would call it a s.h.i.tty bake. I'd say to him, 'Chad, don't worry, it's all good food!' But that was never enough for him. The bread had to be beautiful, too."

After two years, Richard told Chad that it was time for him to move on, that he had learned all he had to teach him. Richard no longer remembers the conversation, but it seems possible that Chad's perfectionism was getting under Richard's skin. That was certainly the case at Chad's next job, working for a former Bourdon apprentice named Dave Miller, at a bakery Miller had taken over in Chico, in northern California. "Chad had very specific ideas of what he wanted in a bread," Dave told me, choosing his words with care. "And I was trying to run a business."

After a year that both describe as uncomfortable, Chad and Dave parted amicably. Chad and Liz headed to southwestern France to work with Richard Bourdon's own mentor, a baker named Patrick LePort, whom both Richard and Chad described as an avatar of wet doughs and whole grains and also something of a mystic. Chad recalls that Patrick would take naps alongside his mixer, because it stood on the precise spot where he had determined that the meridians of universal energy intersected. After a year in France, Chad decided he was ready to strike out on his own. In a house on Main Street in Point Reyes Station, in West Marin County, California, he and Liz opened the Bay Village Bakers; they lived in back. Chad baked in a wood-fired masonry oven built by Alan Scott, a legendary local mason and baker, and over the course of six years in Point Reyes, he worked a.s.siduously, even obsessively, to develop what would become his signature bread-what he describes in his book as "a certain loaf with an old soul."

The first few chapters of Chad's bread autobiography had taken up the entire lunch. Afterward, we strolled back to the bakery to shape loaves. We had mixed the dough before noon, one big batch in a Bongard mixer that can hold and, by rotating its giant steel screw, slowly knead 350 pounds of willful dough at a time. That morning I had helped Chad's young a.s.sistant bakers, Lori Oyamada and Nathan Yanko, empty fifty-pound bags of flour into the mixer. Both bakers were a few years older than Chad had been when he worked for Richard Bourdon, and both, it seemed to me, shared certain attributes with Chad. They looked more like athletes than bakers, with muscled arms (elaborately tattooed, in the case of Nate and Chad) and bodies sleek as cats.

I quickly came to understand exactly how Lori and Nate developed such well-muscled arms. After the dough was mixed and given some time to rest in the Bongard's big stainless-steel bowl, it had to be lifted out, an armful of dough at a time, and transferred to the five-gallon buckets in which it would ferment. This involved rolling up your sleeves, wetting your hands and forearms, and then plunging them deep into the pool of warm dough. By now the gluten was sufficiently well developed to form gigantic, muscular sinews that would stretch but not break no matter how hard you pulled them; after losing a tug of war with one of them, I was forced to conclude that gluten is considerably stronger than I am. Lori showed me how to pinch off a manageable length by squeezing my fist closed way down at the bottom of the bowl. That made it possible to lift out a thick, ropy length of the dough, thirty or forty pounds of the stuff per armful, minus the pound or so that adamantly clung to the hairs on my arms. It took two or three armloads to fill a bucket.

The bulk fermentation was complete by the time Chad and I returned from lunch, so, while Chad picked up the thread of his country loaf's biography, we got to work turning the bubbling white pools of dough out onto the butcher-block counter for cutting and shaping. Using a dough sc.r.a.per, Chad cut two-pound chunks from the ma.s.s, weighed them on an old-time balance scale, and then deftly rotated them with both hands against the floured wood surface until they tightened into nice rounds. To keep them from getting chilled, he gently pressed each shaped round against its neighbor, eventually forming a rolling landscape of powdery white b.u.t.tocks.

It was during the years in Point Reyes that Chad perfected his country loaf, the flavor first, and then the structure. He took from Richard Bourdon the idea of a very wet dough, but he left behind, at least for the time being, Richard's devotion to whole-grain flours and to nutrition as the baker's foremost concern. Compared with Richard (or for that matter Dave Miller), Chad was very much the aesthete, chasing after flavor and beauty rather than nourishment and health. The "loaf with an old soul" that Chad was after was definitely a white bread-he had glimpsed it not just in his mind's eye, but in a specific painting by emile Friant, the late-nineteenth-century French painter.

The painting, which is reproduced in Chad's book, depicts a group of weekend boaters sitting down to a summertime lunch al fresco. One of them is pouring wine while another is holding a gigantic, thickly crusted wheel of bread, from which he's sawing off big white chunks for his friends. At the time, Chad explained, each worker in France was allotted two pounds of bread every day. Bread was elemental food, yet it was also the stuff of ceremony and community-the giant loaves were made for sharing. And for enjoying: In Friant's tender, scrupulous depiction, this looked like a bread you very much wanted to eat.

Chad worked night and day to get the flavor he imagined that bread had. With such a tiny number of ingredients in play, this becomes mostly a matter of manipulating time and temperature. But, as with so much in baking, an iron law of compensation is at work. Any move the baker makes in one direction is liable to produce an undesirable effect in another direction, making trade-offs difficult to avoid. So a longer fermentation might give you deeper flavors, for example, but if the extra time tires out the yeasts, oven spring will suffer. Chad found that if he "r.e.t.a.r.ded" fermentation, by cooling the loaves while they proofed, he could slow down the yeasts while encouraging the bacteria that contribute most to the flavor. He couldn't afford a r.e.t.a.r.der, however, so most nights he stacked his two hundred baskets of shaped dough into the back of his delivery van, a yellow 1953 Chevrolet, and opened all the windows. But though this move gave him the flavor he was after, the loaves came out of the oven flatter than he wanted. A warmer final proof would add air and volume, yet that risked souring the flavor.

The breakthrough came when Chad turned his attention to his starter. "I realized that I needed a younger culture. So I began using smaller and smaller amounts of starter in my leaven, and then less leaven in my dough." He experimented with his feeding schedule, using less starter to inoculate more flour more frequently, so that at each step in the process-starter, leaven, dough-he managed to build a fresher, sweeter, younger culture. In effect, he was resetting the fermentation clock, and the results were immediately apparent.

"I could smell the difference: Instead of being vinegary, like most leavens, mine became fruity, sweet, and floral." These qualities carried over into the flavor of the bread, and the vibrant young yeasts ensured a terrific oven spring. Chad had figured out a way to maximize both flavor and air in his bread, defying, or at least outwitting, the iron law of sourdough compensation.

After the globes of dough had their rest, Chad invited me to try my hand at shaping. My eye-hand coordination is challenged, and I struggled to follow, much less mimic, Chad's lightning-quick manipulations of the dough. I felt like I did the first few times I attempted to diaper Isaac as an infant-clumsy. But Chad was patient, kept feeding me new rounds of dough, and eventually I managed to shape what I, at least, deemed to be some respectable-looking papooses. I did notice, however, that Chad, ever the perfectionist, carefully segregated my loaves from his batch, putting mine into round, rather than rectangular, baskets. I got the feeling that, when and if my loaves were baked, they would not go on sale with the rest.

My time in the bakery had a salutary effect on my baking at home. I felt more fluent in the ways of dough, more comfortable not just manipulating it, but judging its development-and that of my starter-by smell and touch and appearance. Shaping was no longer slapstick. My starter was livelier than ever, some days even exuberant, probably because I fed it more frequently, or perhaps because it had picked up some good bugs from Chad's bakery. My time in the bakery also helped me see that baking by the book-any book-can take you only so far toward a decent loaf, and that that's okay. As I've often heard bakers (and also cooks) put it, the recipe is not the recipe. It never is. It would take a great many more pages than Chad's twenty-seven to capture everything that goes into making a great loaf of bread.

While at lunch, I had shown Chad a crumb shot of my first Tartinian loaf on my phone, the loaf with the sorry case of cavitation. It may not be possible to judge a loaf of bread by its crust, but Chad believes he can judge it by its crumb shot.

"I can see how a bread will taste," he explained matter-of-factly, as if this were normal. But apparently, to the expert eye, the pattern of alveolation and the sheen of its cells tell of the extent of its fermentation and, by extension, its flavor. In my case, the cavitation indicated that my gluten was probably too weak to contain the gases in their cells as they expanded in the heat. The bread was rising faster than the gluten could stretch, so the gas was busting out, then pooling beneath the hard roof of crust. A few more folds might help to strengthen the gluten, he suggested, as would a longer, slower fermentation. Chad thought I should try overnighting my dough in the refrigerator before baking.

This gave me my breakthrough. The very first loaf I r.e.t.a.r.ded overnight in the refrigerator emerged from the oven a thing of beauty. The loaf had achieved an oven spring just this side of spectacular, and its crust, which in all my previous efforts had been a tentative, wan shade of brown, was now deeply colored, forming a dark, weather-beaten hide rent across the top by a sharply turned and blackened ear. This crust had conviction. As for the crumb, I had to wait an hour for it to cool, but when I finally sawed off a slice, I exposed a cross section of evenly distributed holes in various sizes, their stretched walls glistening just slightly. True, my crumb was somewhat tighter than Tartine's, the alveolation not nearly so shiny or wild, but this looked like a fine loaf of bread, and I felt an upwelling of pride the force of which took me by surprise. This was immediately followed by the sagging realization that my proud achievement, the product of so many weeks of work and study, would soon get eaten and be forever lost to history.

So I took its picture. I briefly considered posting it to TheFreshloaf.com, thinking I could impress the bread geeks with it, but the impulse soon pa.s.sed. Too peac.o.c.ky. I did text it to Chad, however. "Nice loaf," he texted back, a little more laconically than I had perhaps hoped-I felt like I had been patted on the head-but I didn't mind. The bread was delicious: sweet, a little nutty, with just the slightest acid tang. Judith and Isaac, at least, were suitably impressed, and together we worked through the great white loaf, first at dinner that night, then at breakfast the following morning, when it made some exemplary toast.

I have spent some time trying to pa.r.s.e the almost absurd pride I felt about this loaf and various others I've baked since. I mean, a loaf of bread, big deal. And yet it did feel big. I couldn't imagine feeling quite this way about a great stew or braise, much less taking its picture and texting it to someone or posting it online.

The only thing I've cooked that prompted the same impulse to show off is a whole barbecued hog, whose appeal, especially to the male ego (large beast killed; food enough to feed a village), is all too obvious. But what is it about a loaf of bread, something that is much smaller and yet in some ways even more impressive?

Part of it is aesthetic-the satisfaction of making something, something beautiful that didn't exist before. A good-looking loaf of bread declares itself as an artifact, an original, man-made, freestanding object, something that cannot be said of too many other foods. Most foods, even the whole hog, are altered versions of nature's already existing animals and plants, which more or less retain their form after cooking. But a loaf of bread is something new added to the world, an edged object wrested from the flux of nature-and specifically from the living, shifting, Dionysian swamp that is dough. Bread is the Apollonian food. Which might explain some of its appeal to the male ego, as might the miraculous fact that it rises.

Yet the pride I felt wasn't only aesthetic or, for that matter, necessarily masculine. It had more to do, I think, with the sense of personal competence my success conferred. Or at least that's how it felt to me. Bread is such a fundamental necessity and comfort of everyday life, as it has been in the West for at least six thousand years. And yet in our time the ability to make this necessary thing has pa.s.sed out of our hands and into those of specialists. Whether artisans or corporations, it makes little difference: The only way for most of us to obtain it is to trade our professional labor for theirs. I doubt baking bread is something I am ever going to do more than every once in a while. Yet the fact that doing so is now solidly within the orbit of my competence, that my hands now know how to transform a pile of cheap flour and free water (free microbes, too!) into something that will not only nourish but also give so much pleasure to my family, changes everything. Or at least changes me. I am a little less dependent, and a little more self-reliant, than I used to be.

And then there is the matter of the air itself. (Or is it the antimatter?)

To compare a loaf of bread with a bowl of porridge is to realize how much of bread's power, sensory as well as symbolic, resides precisely in those empty cells of s.p.a.ces. Some 80 percent of a loaf of bread consists of nothing more than air. But air is not nothing.

In bread, it is where much of the flavor resides, and is the reason bread is so much more aromatic than porridge. The air trapped in the alveoli conducts bread's aromas-the two hundred or so volatile compounds that have been identified in a well-baked sourdough-to the back of the mouth, where they then drift up into the nasal pa.s.sages and, by means of retronasal olfaction, reach the brain.

"Retronasal olfaction" is the technical term for our ability to smell food that is already in our mouth. Whereas the nose's olfactory sense-"orthonasal olfaction"-identifies smells when we sniff in, retronasal olfaction identifies smells when we breathe out, as the molecules released from our food rise from the back of the mouth up into our nasal pa.s.sages. Orthonasal olfaction allows us to identify smells from the outside world, including smells from foods we are deciding whether to ingest. The purpose of retronasal olfaction is different, as is the range of compounds it detects and the regions of the brain to which it reports. The signals from retronasal smell are interpreted at the highest cognitive levels of our cerebral cortex as well as in regions involved in memory and emotion. This has led some scientists to hypothesize that the function of retronasal smell may be primarily a.n.a.lytical, helping us to archive the vast catalog of food flavors and record them in memory for future use.