Cooked: A Natural History of Transformation

by Michael Pollan

  Not a very eagle-y eye, apparently. Because I have no recollection of the plastic container beginning to bulge, slightly at first, and then cartoonishly, as the carbon dioxide built up inside it. What I do remember, with a pained clarity a half century later, is coming home with my parents late one evening and flicking on the lights to find the white walls and ceiling of our living room evenly spattered with splotches of dark purple. Some were just smears of purple pigment; others drooled jagged slivers of grape skin like wet confetti. Ecstatic fruit flies were everywhere, and the living room had acquired an unmistakable new smell. It smelled like wine!

  “Plenty were drunk with nectar,” Plato writes, referring to mead, or fermented honey, “for wine was not yet invented.” Wine made from honey was probably the first alcoholic beverage humans fermented on purpose. (And when we read of the ancients’ fondness for nectar, we can safely assume they’re talking about fermented nectar.) Alcoholic fermentation depends on sugar, and, at least before the advent of agriculture, the sweet nectar that bees concentrate into honey was the richest and most readily accessible source of sugars in nature. In the hive, however, honey is so completely saturated with sugar that nothing can live in it, yeasts included. The hydrostatic pressure will promptly suck the water out of any microbe that falls into it. This of course is exactly what the bees want. But I read (in Sandor Katz’s book) that as soon as honey is diluted with water it will spontaneously begin to ferment.

  I was curious to find out if making mead was really that simple, and, if it was, to sample what the very earliest alcoholic beverage might have tasted like. I happen to be blessed, or cursed, with a ready supply of honey: My friend Will Rogers keeps bees in a neighboring town, and I seldom visit him without coming away with yet another pint jar of the stuff. By now I had an entire shelf of honey jars in the pantry. It’s a delicious, cosmopolitan sort of honey, a distillation of the diverse riot of flowering plants that, here in the East Bay, are in bloom every month of the year.

  So I diluted a pound or so of Will’s honey in a gallon jug of water, one part honey to four parts water, and fitted the jug with an airlock. This is a cork attached to a curvaceous piece of plastic piping with a little reservoir of water at the bottom of a bend that keeps oxygen from getting in but allows carbon dioxide to escape. Every day I checked in on my jug, examining it for fizz or escaping gas bubbles, but the pale-gold liquid gave no sign of life. It might as well have been a lump of coal under a Tensor lamp.

  I was tempted to add some yeast to get things going. That’s what Will had suggested, as had the fermentos down at the Oak Barrel, the local home-brewing supply store where I purchased the airlock. But after spending time with Sandor Katz, I was attached to the idea of a wild fermentation using local yeasts. So I e-mailed Sandor for advice.

  “What I would have recommended that you do differently,” he wrote back, “is to leave the diluted honey in an open vessel for a few days and stir frequently until bubbling becomes evident, and only then move to an airlock.” It seems that the aeration stimulates the yeast, the spores of which might be in the air or in the honey itself.

  His advice was based on an unusual fact about the particular yeast I was trying to entice. Saccharomyces cerevisiae is a microbe that can operate equally well aerobically and anaerobically, employing a completely different metabolic pathway depending on the conditions in which it finds itself. In evolutionary terms, this dual metabolism is a newish development for S. cerevesiae. Before the advent of the flowering plants (and their fruit) some eighty million years ago, the yeast’s ancestors relied strictly on an aerobic mode of metabolism to generate energy. This system was highly efficient, and, among yeasts, nothing out of the ordinary. After the angiosperms arrived on the scene, however, S cerevesiae acquired a new bag of metabolic tricks that gave it a tremendous edge over its competition: the ability to survive in the airless conditions deep within a fruit or nectar, and, once there, to transform sugars into alcohol. This new metabolic pathway is a less efficient way to generate energy—the alcohol produced by it still has plenty left to burn—yet it has the considerable advantage of expanding the yeast’s habitat and poisoning its competition—not to mention endearing itself to some of the higher animals, notably including ourselves.*

  Because aerobic metabolism gives the yeast the maximum amount of energy from its food, oxygenating the liquid in question is a good way to kick-start a fermentation. So I started a new batch of mead, diluting the honey with four parts water and leaving it out on the kitchen counter for several days, uncovered. I had read that mead was often flavored with various herbs and spices, in order to contribute a bit of acidity, some tannins, and nutrients for the yeasts, so I added a bay leaf, some cardamom seeds, a star anise, and a few tablespoons of black tea. (Mead to which such herbs and spices are added used to be called “metheglin.”) And just in case I lacked for wild yeasts, I dropped in an overripe, split fig from the garden that I figured must be crawling with them.

  Every time I passed the bowl of honey water, I gave it a vigorous stir with a wooden spoon, working a little more air into it. After about a week, I noticed a fizz of tiny bubbles on the surface. Day by day, the bubbles got a little bigger and more vigorous. When I thought I could detect the faintest smell of alcohol, I poured the liquid into the jug and plugged it with the airlock. The very next day I had the satisfaction of watching a nice fat bubble of carbon dioxide shoulder its way through the pocket of water in the airlock. Fermentation!

  The jug perked along for a week or so, rhythmically emitting a bubble every several minutes, and then seemed to grow quiet. A shake of the jug would enliven things for a few hours, but after a while the fermentation had subsided for good. It was time for a taste. So I pulled out the airlock and poured some of the liquid into a wine glass. It was golden but cloudy, like a pale, unfiltered cider.

  I could smell the alcohol and the sweet spices. The mead had a light fizz on the tongue and tasted like a mulled wine, sweet and a bit heavy. So this was metheglin. It wasn’t half bad, I decided. Definitely interesting. But perhaps a little too sweet to drink in any quantity. Clearly the wild yeast had thrown in the towel before completely fermenting all the sugars in the honey.

  Apparently this is often the case with wild yeasts. They will ferment a sugary liquid only up to about 5 percent alcohol, at which point they “crap out,” as Kel Alcala, the young guy behind the counter at the Oak Barrel put it. It seems that 5 percent alcohol—or ten proof—is fairly standard for a fermented beverage in nature. This could explain why alcoholism doesn’t appear to be much of a problem in the animal world. Also, honey presents special challenges to yeast, since it contains various antimicrobial compounds to prevent it from spoiling; from a bee’s perspective, fermented honey is spoiled honey. Kel recommended that, for my next batch, I try some champagne yeast, and he sold me a packet. “I call it the killer yeast,” he said. “It’ll ferment anything you throw it at, until it’s pretty much bone dry.”

  I was curious to try it. But, honestly, I was impressed with what my local wild yeasts had accomplished on their own, completely free and voluntary. They had made me a jug of mead after all, Beowulf’s drink of choice. It was low proof, true, but an alcoholic beverage just the same. By the time I finished the glass of mead, I felt a pleasant buzz in my brain, a mild and agreeable lightness. This mead might not impress the boys at the Oak Barrel yet, but as my first home brew (not counting the living-room-ceiling cuvée of my childhood) it felt to me like an achievement.

  Figuring out how to make something like my mead was a development of inestimable value to our ancestors. Leaving aside for a moment the blessings of intoxication—which were mixed, it’s true, but on balance a bo
on—fermented drinks offered a great many other benefits to early humans. Mead and beer and wine were safer to drink than water, since the alcohol in these drinks (and the fact that some of them, like beer, had been boiled) killed off any pathogens in the water. As in the case of so many other fermentations, the process itself rendered the original food or drink more nutritious, less perishable, and more interesting than it had previously been. The yeasts that fermented my honey water also contributed vitamins (B-complex), minerals (selenium, chromium, copper), and protein (the multiplying yeasts themselves). Some anthropologists believe that beer making, which began in earnest around the same time that farming did, helped the early agriculturists compensate for the decline in the nutritional quality of their diet as they turned from hunting and gathering a great many different foods to a monotonous diet of grains and tubers. The B vitamins and minerals in beer, for example, helped compensate for the loss of meat from their diet.

  The alcohol itself probably contributed to the health, as well as the happiness, of ancient people. Alcohol is a rich source of calories as well as nutrients. People who drink in moderation (which a 5-percent mead pretty much guarantees) live longer and endure lower rates of many diseases than both people who don’t drink at all and people who drink to excess. The exact mechanisms for these effects have yet to be identified, but the scientific consensus today is that drinking alcohol (of any kind) in moderation protects against heart attack, stroke, type 2 diabetes, arthritis, dementia, and several types of cancer. The teetotaler is at greater risk for disease and early death than the drinker.

  Alcohol is a powerful and versatile drug, and for most of human history was the most important drug in the pharmacopeia—a panacea, literally. It reduces stress. It also muffles pain, and for most of history served as humankind’s principal analgesic and anesthetic. (Opium probably wasn’t cultivated until 3400 B.C.) Also, many of the plant drugs, like opium, require alcohol as a solvent to unlock their powerful chemistries and make them available to us. In fact, it was once common practice to add various psychoactive plants (including opium and wormwood) to beer and wine; the addition of hops flowers to beer is all that remains of that venerable tradition.*

  We humans owe a large debt to S. cerevisiae. Were it a creature that people could see, they might well decide this yeast has a stronger claim to the title of man’s best friend than the dog. Some evolutionary biologists contend that it was the world’s very first domesticated species. Using DNA analysis, they’ve constructed an evolutionary tree for S. cerevisiae demonstrating that, more than ten thousand years ago, it diverged from a few, and possibly just one, wild ancestor into several distinct strains under the pressure of human selection. When humans began making mead and wine, brewing beer and sake, and baking bread, the yeast evolved and diversified to take maximum advantage of the rich new opportunities, or niches, humans presented it—whether a mash of grain, or diluted honey, or pressed grapes. Several thousand years later, the various strains of S. cerevisiae exhibit substantially different qualities, levels of alcohol production (and tolerance), and flavors. The process of “artificial selection” that shaped these yeasts is much like the one that transformed the wild wolf into a variety of different dogs, except that in the case of S. cerevisiae, the selection came earlier and was entirely unconscious.

  In some cases, S. cerevisiae appears to have hybridized with other yeast species to acquire the genes it needed to make the most of a human fermentation opportunity. Consider lager, the class of light, effervescent beers made by fermenting a mash of grain under cold conditions. Most strains of S. cerevisiae go dormant at temperatures below 55°F. But when people in Bavaria began trying to ferment beers in caves during the winter, a novel strain of yeast that could thrive under those conditions soon appeared. (We now know it as Saccharomyces pastorianus.) New tools of genetic analysis indicate that this hearty lager strain contains genes from a distantly related species of Saccharomyces, called Saccharomyces eubayanus, that has been traced to Patagonia, where it is found on the bark of certain trees.* Researchers hypothesize that, shortly after Columbus’s voyages, this cold-tolerant yeast found its way to Europe, perhaps in a shipment of lumber, or in a barrel that was then used to brew beer. So it appears that lager, like the tomato and the potato and the chili pepper, is yet another gift from the New World to the Old, tendered as part of the Columbian Exchange.

  S. cerevisiae has demonstrated remarkable ingenuity in exploiting the human desire for alcohol, particularly in finding ways to transport itself from one batch of the stuff to another. Some strains get themselves passed on by colonizing the vessels in which alcohol is fermented, or the wooden tools used to stir the pot. “Brewing sticks” are prized possessions in parts of Africa, believed to inaugurate the miracle of fermentation when used to stir a mash—and so they do, much like Sister Noëlla’s wooden paddle. Other yeasts, like the ones that give us ale, evolved the trick of floating to the top of a fermented liquid, where they are much more likely to hitch a ride to the next sugary feast. That’s because brewers typically scoop yeasts from the top of one batch to start the next. The most successful yeasts were the ones that learned to clump together and then float to the surface by attaching themselves to the rising bubbles of carbon dioxide—a conveyance that they of course created.

  But surely the greatest evolutionary trick of all came when S. cerevisiae first figured out—unconsciously, of course—that the very same molecule it had originally devised to poison its enemies was also capable of making it a coevolutionary partner as powerful, ingenious, and well traveled as Homo sapiens. The human desire for alcohol has been a tremendous boon to Saccharomyces cerevisiae. To supply it with endless rivers of liquid substrate to ferment, we have reconfigured vast swaths of the earth’s surface, planting tens of millions of acres of grain and fruit, in the process creating a paradise of fermentable sugars to sustain this supremely enterprising family of fungi.

  In the 1980s, an anthropologist at the University of Pennsylvania by the name of Solomon Katz put forth the arresting theory that it was the human desire for a steady supply of alcohol, not food, that drove the shift from hunting and gathering to agriculture and settlement. Beer, in other words, came before bread, and as soon as people got a taste of it, Katz reasoned, they would have wanted more than could be produced by gathering seeds or fruits or honey. The hypothesis is difficult to prove, but plausible. It would certainly help explain why early humans would ever have traded the comparatively easy lifestyle of the hunter-gatherer, who typically devotes far less time and effort to obtaining food than the farmer, for the toil and inferior diet of the early agriculturist. A reliable supply of food is much easier to secure in the wild than fermentable sugars, which tend to be rare and hard to find. There is only so much honey in the forest, and what there is, is well defended by bees. The only way to guarantee an adequate year-round supply of fermentable sugars would be to take up agriculture. Analysis of yeast DNA indicates that the domesticated strains go back at least as far as the domestication of grain, and perhaps further.

  One suggestive new piece of evidence for the beer-before-bread hypothesis comes from the analysis of the carbon isotopes in the skeletons of ancient people in South America. Though corn had been domesticated by 6000 B.C., bones from the period immediately following give no evidence of corn proteins in the diet. This suggests that people were consuming the corn they were growing not as solid food but as an alcoholic beverage, since alcohol made from corn would contain little protein, hence leave little trace of it in bone. So it appears likely that Native Americans were drinking corn before they began eating it.

  Yet it isn’t at all self-evident how one would go about turning a pile of corn, or a
ny other grain, into alcohol. To learn how to make beer is to marvel at the ingenuity of the people who first figured it out. The process is much more complicated, and involves many more steps, than making mead, or for that matter wine. Charlie Bamforth, the Anheuser-Busch Endowed Professor of Brewing Science at the University of California, Davis, likes to begin his lectures with a little joke. “Do you know why Jesus performed the miracle of turning water into wine? Because it’s so much easier than making beer!”

  Corn kernels, like the seeds of many other grasses, contain plenty of sugars, but they are not in a form that S. cerevisiae can make use of. The sugars are tightly bound together in long carbohydrate chains that the tiny yeasts can’t break apart. This well serves the seed, which has an interest in keeping its precious cargo of sugars intact and safe from microbial attack until the germinating plant needs them. But certain enzymes can cleave those carbohydrate chains into simple, fermentable sugars, and, as the earliest beer makers discovered, one of those enzymes—ptyalin—is present in human saliva. The first beers were made by chewing kernels of corn and other seeds, mixing them with saliva, and then spitting the resulting slurry into a vessel, where it would readily begin to ferment. (The desire for an alcoholic drink must have been keen indeed.) To this day, there are indigenous groups in South America that rely on the chewing method to make an alcoholic beverage called chicha—a corn-and-saliva beer.

  Surely there had to be a better way, and eventually it was discovered. Instead of chewing the grain to release its sugars, our ancestors figured out that if they briefly germinated the seeds before mashing them in water, the mash would become sweet enough to ferment. Malting, as this process is called, is essentially a way to trick the seed into releasing its own diastatic enzymes, to break down its carbohydrates into sugars to nourish the (supposed) new plant. In beer making, seeds of grain, most often barley (which contain high levels of both fermentable sugars and enzymes), are moistened and allowed to germinate for a few days before being dried in a kiln. The heat kills the embryonic barley plant, but not before the enzymes have been released and begun breaking down the seed’s stash of carbohydrates.