Proof: The Science of Booze

by Adam Rogers

Yeast lives as a single-celled organism that is neither plant nor animal, neither bacteria nor virus. The fungus family includes every mushroom you’ve ever seen, lichens, rusts and smuts, athlete’s foot and the Candida that infects people’s most intimate parts, Dutch elm disease, the parasite that causes dandruff, and slime mold, the single largest creature on earth.

meaning “to lift,” as in rising bread. The English “yeast” comes, via the Dutch “gist,” from the Greek word for boiling. Getting the gist of something is literally boiling it down.

Chemists and biologists have always been at odds; chemists think that they’re explaining at a more granular level of detail what biologists purport to study more holistically. (And physicists? Don’t get them started.)

Berzelius is the scientist who first called molecules that contained only carbon, hydrogen, oxygen, and nitrogen “organic,” because they’re found in living things—thus inventing “organic chemistry,” the college course that destroys the hopes of so many kids who think they’re going to be doctors.

Saké: The Essence of 2000 Years of Japanese Wisdom Gained from Brewing Alcoholic Beverages from Rice.

The existence of beer (made from grain) and sake (made from rice) prove that both cultures—Asia and the West—solved that problem. But they did it with radically different approaches, two roughly parallel developments that probably say more about the centrality of booze-making technology and of sugar itself, as a molecule, than they do about cultural differences.

Koji does something that sounds simple, but is actually a little miraculous: It turns starch into sugar. Takamine didn’t know how—nobody did—but he knew that if he could work it out, it could make him rich. Sugar is the most important molecule on earth. You may think water deserves this title. I get it. Water is really good at dissolving other molecules and carrying them around, both inside our bodies and out in the world. Water lets chemicals bump into each other and then do interesting things. But calling water the Best Molecule is like giving paper the award for Best Book. Water is the medium, a backdrop. Sugar is fuel.

We humans can digest starch. Yeasts can’t. Without simple sugars, there’s no fermentation, and without fermentation there’s no alcohol. So this is where yeasts, tricky little bastards that they are, have managed to teach us a few tricks. Remember those dogs acting all juvenile and cute in return for easy meat and a place at the fire? Yeasts learned to roll over and play fetch, too—in return for access to sugars they couldn’t get at on their own. We learned to break apart the complex sugar polymers in grain so we could feed them to a fungus. We domesticated yeasts; yeasts domesticated us.

So let’s build the ideal booze substrate. We need a fruit that grows widely and easily, with a high sugar content. It should maybe have some interesting flavors, or be easily manipulated into having interesting flavors. It should be easy to harvest and easy to ferment. What we’re looking for is the grape.

One way to think about sugar is that it’s the way living things store and move carbon.

grapes are right near the top among fruits in terms of storing carbon as simple, monosaccharide sugars. The fruit is one-quarter sugar, and half of that is glucose.

But grapes “don’t make a lot of esters at all,” says Paul Boss, a plant molecular biologist with the Commonwealth Scientific and Industrial Research Organisation in Adelaide, Australia. That’s good news for winemaking, because the chemical process of fermentation would destroy whatever esters the grape came up with. But the grape makes molecules with the potential to become esters when the juice gets turned into wine.

once you can settle down long enough to collect a bunch of grapes, it’s actually hard not to make wine. Just bruise the grapes and come back later. They’ll ferment on the vine. Domesticated grapes, the grapes we use for wine today, make all the right molecules, grow to the right size, achieve the right Brix (the unit winemakers use to measure sugar), and in general sit and roll over on command.

So what gave the grapes such an aptitude for booze? They were easy, for one thing. Grapes grow in places other plants can’t, in soil other plants can’t use. Their tendrils let them climb on other crops, or amid scrub or trees. They grow extended vines called lianes, but they can survive pruning.

Their chemistry, too, is perfect. Most of the fruit is pulp, or what botanists call mesocarp, and most of that pulp is made of the sugars glucose and fructose, as well as tartaric and malic acid, a yeast-friendly mix.

All that handling of barley, getting it soaking-wet and then air-drying it, tricks the barley embryo into thinking that it’s time to start growing. It triggers a chemical cascade, starting with the production of a hormone called gibberellic acid, which then courses through the aleuron layer. That’s a signal to those cells that they should start making enzymes—amylases that can break down starches and proteases that can break down the protein coatings around those starches.

It’s crunchy, like a Japanese rice cracker, and the sweetness has mellowed from something Cheerios-like to porridge with syrup. The phenols from the peat ring out clearly; it’s medicinal in that way that seems lovely if you’re the kind of person who thinks that peat is lovely. It’s finished, in other words. It’s waiting to be whisky.

That polished rice gets steamed, filling a sake brewery with one of the most comforting smells in the world, a heavy, sweet, nutty aroma.

no gene is an island; they’re chained together and packed into structures called chromosomes. Rokas hypothesized that domestication—that is, selection for a certain trait encoded by a certain gene—also reduced variation among neighboring genes. You get the genes that break down starch in rice, sure, but you also get whatever is sitting next to them on the chromosome.

strains he buys from three different producers. The smell of the culture room changes as the koji fungus spreads its tendrils through a batch of rice, shifting from a homey, comforting cooked-rice smell to something more like roasted chestnuts or, if it goes a bit longer, the earthy smell of mushrooms. The rice, now also called koji, tastes different—sweeter, as you’d expect, and a little like popcorn.

I take a sip of the 810 and a long sniff, put the glass down. I do the same thing with the 860. They’re crisp and hoppy, like a pine forest crossed with ocean foam, but honestly, I can’t tell much of a difference between them.

White Labs once made two beers with the same wort and the same yeast—the same everything, in fact, except the temperature of the fermentation. The beers tasted completely different. The beer fermented at 66°F registered a scant 7.98 parts per million of acetaldehyde, which usually has a sort of green-apple taste, but that’s below most people’s threshold for being able to taste it at all. The one brewed at 75°, meanwhile, had a whopping 152.19 parts per million.

Ethanol is a particularly cool molecule. It’s a solvent, which means lots of different molecules that don’t dissolve in water will dissolve in a solution of ethanol. It’s odorless, colorless, and it burns really well—a sign of a good fuel. It’s also a potent microbicide. When yeasts squirt it into their environment, it kills off local bacterial and fungal competition. Now, yeasts can actually reverse that part of their metabolism—they can slurp back up the ethanol they’ve made to use as an energy source, as food. It’s like a car running on its own exhaust—in times of emergency, yeasts can live on their own poop.

Fermentation isn’t an accident, or a byproduct. It’s the way yeasts convert what they eat to energy. That’s metabolism, a long sequence of chemical reactions, nipping away atoms here and adding them there, attaching and detaching electrons, all in the service of creating a molecule called ATP, adenosine triphosphate. Inside a living thing, ATP is energetic currency, the stuff that keeps the lights on.

We mammals start with oxygen and glucose and end, essentially, with the waste products carbon dioxide and lactic acid. It’s the same stuff that spoilage bacteria make, and the same stuff in pickles. But yeasts end up not with lactic acid but with another molecule, acetaldehyde. And they don’t stop there. Yeasts string hydrogen atoms onto that, making ethanol and ATP, and then the ethanol diffuses into the environment. Yay! We have made booze.

It’s the same thing linguists do when they look at the way all the Indo-European languages say “home” and make a really good guess about what the word for “home” was in proto-Indo-European. “The idea was, if you could resurrect ancient proteins, bring them back to life, and study them in the laboratory, you might be able to understand physical behavior,” Benner says. His team called their new approach “paleogenetics.”

Yeasts eat sugar, but 150 million years ago, grasses hadn’t evolved yet, and sugar cane is a grass. There weren’t any flowering, fruit-growing plants yet, either. And yet somehow yeasts survived just fine.

Ethanol is highly volatile—it readily evaporates. Yeasts weren’t trying to sterilize their surroundings. All they want to do is get their garbage out of the house, and packaging it as ethanol was the most efficient approach. Then the angiosperms came around. “Now they’re living in fleshy fruit,” says Benner. “But they’re already resistant to ethanol. So the yeast is now all of a sudden pre-evolved. You’re looking at what appears, in retrospect, to be the yeast getting ready for fruits. But that’s not right.”

The colors of beer, on the other hand, are mostly molecules called melanoidins (same root as melanin, the pigment in skin). The heat of the kiln during malting induces the Maillard reaction in the barley sugars and amino acids—just like browning in a Dutch oven. Since barleys intended for ales tend to be kilned for longer, ales tend to be darker in color.

even with just one grape juice, the researchers saw variations up to a thousandfold in how much of a given chemical the yeast made, and they all did it at different speeds, too.

Sauvignon Blanc grapes. They’re full of chemicals called thiols. (Their distinguishing trait, chemically, is that they contain sulfur.) In grape juice, those thiols are connected to an amino acid called cysteine, which makes them nonvolatile, and as a consequence we can’t smell them. “But yeast has a limited capacity to decouple thiols from cysteine,” says Pretorius. “That gives you that typical Sauvignon Blanc ‘passion fruit’ or ‘tropical fruit’ flavor.” The compound comes from the grape, but the yeast—as part of its metabolism of the juice—makes it volatile. The same goes for the rosy- or violet-smelling terpenes in Gewürztraminer grapes. In the juice they’re bound up, nonvolatile. Yeast liberates them.

Scientists are only now trying to get specific about which microbes are most important in various drinks. In the musts of Napa Chardonnay they find the families Firmicutes and Eurotiomycetes (that latter includes Aspergillus and Penicillium fungi). But in California’s Central Coast winemaking region it’s Bacteroides, Actinobacteria, Saccharomycetes, and Erysiphe necator. Back up to Sonoma and you get B. fuckeliana and Proteobacteria. And other grapes have entirely other colonizers, each contributing in ways as yet unknown to the final flavor. The researchers who parsed all that call it “microbial terroir.”

Carbon dioxide has its own flavor, which affects the overall taste of a drink. (At high partial pressures—which is to say, when a gas contains lots of CO2 relative to other gases—it also sets off the body’s pain receptors, called “nociceptors.” One trick almost every distiller I visited tried to play on me was to get me to stick my head into the vat during the final stages of fermentation, when the headspace—the volume of air above the liquid—is a cloud of CO2. Taking a whiff is like sticking a knitting needle up your nose. Too much of it, and you can pass out and fall right into the vat.

In sparkling wines like champagne or prosecco, little bubbles pull fatty acids and other aromatic chemicals from the liquid to the surface. When they hit the top, they pop—a hole opens at the top of the bubble, its edges expanding at 22 miles per hour and converting to a ring of high pressure that smacks into a low-pressure region at the bottom of the bubble. The collision squirts a conical jet into the headspace of the glass that improves (or at least accelerates) the wine’s perceived aroma. Also, the little splashes tickle.

Ideally, a glass of sparkling wine will form bubbles more subtly than the geyser from the neck of a bottle. For that to work, gas molecules have to find each other in the glass amid all those molecules of liquid. The problem is, the liquid molecules stick together. The CO2 is like the lovers at the end of a romantic comedy, and the liquid is the crowd at the airport they have to fight their way through about ten minutes before the end.

As soon as beer hits the inside of a glass it starts to froth; by the time the glass has even a little liquid in it, beer is building a head of foam. Over a few minutes, the foam subsides. It seems simple enough, but that rise-and-fall is actually the macroscopic expression of a fierce battle on the microscopic scale. Physics wants to pop those bubbles; chemistry wants to hold them together.

Dogfish Head makes a bunch of brews with ingredients based on McGovern’s research. For one based on an Egyptian recipe, the brewers even captured wild yeast from an Egyptian date farm.

the bartender tells us he has another Dogfish Head brew called Theobroma. It’ll do. McGovern orders us a bottle. “It’s based on our analysis of very early chocolate from Honduras,” he says as the foam settles over pitch-dark liquid. “Originally they had the chocolate tree with its fruit. The beans are surrounded by a pulp with 15 percent sugar, and that has to be fermented away to get to the bean. In the process you get a 7- or 8-percent-alcohol beverage. We think that may be why people got interested in domesticating chocolate, because it made this elite beverage.”

I take a sip, and it’s everything a chocolate egg cream should be. And then heat blossoms at the back of my throat. McGovern takes a big swallow of his and says, “It also has ancho chiles.”

Every four seconds, someone on earth buys a bottle of Glenlivet.

In Scotland, spirit safes used to be locked; only the Queen’s revenuer had the key, because the thermometer and hydrometer that measured alcohol content were inside the safe, and that’s what they based taxation on.

All the technology changes the room in one huge way: It doesn’t smell like a distillery. No bread aromas, no scent of nail-polish remover or vanilla spice. Nothing. It smells like an office.

just because Jack Daniel’s comes from a chemical plant doesn’t mean it isn’t a damn-fine-tasting chemical.

We distill knowledge to its essence the same way we distill fruit wine to brandy, beer to whisky, fermented sugar cane juice to rum.

The writer Primo Levi called the series of phase changes built into distillation—liquid to gas to liquid—magical transformations in pursuit of the fundamental spirit of life.

Distillation tells us that having less of something can make it more potent. It is co...

If a fig spontaneously ferments in the forest, a monkey is there to hear it. (And eat the fig. And get drunk.)

Credit for the still goes instead to ancient Egypt, to an alchemist named Maria Hebraea, more commonly called Maria the Jewess. She was a scientist from the scholarly city of Alexandria sometime between the first and third centuries. And it’s . . . possible. Even though the history is sketchy, Alexandria was the kind of town where a Jewish woman researcher could have invented one of the most important pieces of lab equipment in history.

man named Hero was the best-known maker of the devices. His clockwork designs, driven by heat, pressure, gravity, and magnets, included temple doors that opened only when a fire was lit in front of them, a holy water fountain that flowed when a supplicant dropped a coin into it, an orrery that moved by itself, a trumpet-playing robot, mechanical birds that really sang, and a theater where everything—sets, actors, curtains, and special effects—was automated. Hero also invented a device called an aeolipile, two copper tubes leading up from a sealed container and into a freely rotating sphere. The sphere had outlets on two sides; boil water in the lower container and steam would shoot out of the outlets, making the sphere spin. The aeolipile was, before anyone knew what to do with such a thing, a steam engine.

The first centuries AD were a high point of wine production by Roman military veterans in southeastern France, and they exported this wine throughout the empire. The amphorae that carried it have been found in Egypt, so it’s possible Alexandrian distillers had access to French wine. If you worked in the lab that invented the still, you’d at least run some wine through it after hours, wouldn’t you? Just to see what would happen?