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Humankind’s Ascent Took Path of Yeast Resistance

• July 11, 2011 • 3:50 PM

There’s a strong case to be made that the first species cultivated by humankind was brewer’s yeast, and a generation of researchers will drink to that.

Once upon a time there were no farms. People ate fruit off the vine and killed animals as they ran. They roasted things when it suited them but just as often ate them raw. The world was like this for thousands of years, a place of arrows and nuts where everything that was necessary could be found. One might imagine many reasons for giving up on those old, superficially idyllic, ways. Perhaps it was hunger, that ultimate mother of invention, or maybe it was just invention itself, unmotivated by need.

But these are not the only options. Solomon H. Katz at the University of Pennsylvania thinks it was beer.

Yes, beer. Katz’s argument is that once beer was invented, people would have liked it and wanted more of it, more than could be made out of gathered seeds.

Imagine the scenario: An early Egyptian left wild wheat or some other grass seed in water. Maybe he had intended to make gruel, but he left it too long and the slurry sprouted (and happened to have fermented, as well). Yet, because he was hungry or thirsty or simply dissatisfied, he drank it anyway. When he did, voilà! With that (little) buzz was born the germ of the need for agriculture.

Or at least this is part of Katz’s idea. He also thinks that beer is, or at least was, good for us. Beer, he has suggested, is healthy when compared to the raw products out of which it is typically made.

Relative to raw wheat or barley, for example, beer is enriched in some fats, vitamin B and the amino acid lysine. Relative to the water likely to have been found in early human settlements, the first beer is also likely to have been less ridden with pathogens. Fermentation purifies. It may be a stretch to say that beer does the body good, but relative to our early alternatives, it probably did the body better (as by some measures it continues to do today).

Katz’s beer hypothesis was debated actively in the late 1980s in scientific papers and Pennsylvania bars. It led to attempts to recreate the first beers (e.g., Anchor Steam’s Sumerian brews or Dogfish Head’s ancient ales) from what has turned out to be the oldest discovered recipe. It also fueled the scientific careers of young, excitable scientists and helped usher in a new wave of research at the University of Pennsylvania — think of this as an Indiana Jones of ancient potables — on the history of food and booze.

But with time, Katz’s idea lost some of its shine. It was not proven wrong so much as proven difficult to prove. Anthropology is full of such ripe but hard-to-reach fruits.

When Katz (now, a bit ironically, director of the Krogman Center for Childhood Growth and Development) first offered his hypothesis, the evidence he brought to bear was the standard stuff of anthropology — potsherds, ancient writing and burials mixed with a pinch of raw insight. But times have changed a great deal since the 1980s. Modern genetics now allows scientists to see the invisible genes lurking in all things living and dead, including beer, and with them, more of the hidden story.

What Katz knew but tended to ignore when he first considered the story of beer was that it was not the only fermented drink important to the human story.

Fermented drinks and foods, from beer to sake, bread to wine, are consumed in West Africa, China, Japan and have, almost certainly, been consumed in one form or another since before the first seed was sewn (some monkeys are even known to seek out fermented fruits and suffer the stumbling consequences). The eminent anthropologist Claude Lévi-Strauss regarded the invention of alcohol — though perhaps discovery is the better word — as a marker of the passage of peoples from “nature to culture.” Fermented alcoholic drinks have been documented from settlements more than 7,000 years old in China, 5,000 years ago in Mesopotamia and only slightly later in Egypt. In each place where alcohol has been made, it has been regarded in one way or another as special food both for the Pharaohs or kings and the afterlife. Even Noah, who had space for just two of each animal on the ark, made sure to leave some room for beer.

In the last three years, scientists have begun to revisit the links between civilization and beer, and between civilization and wine, sake, other fermented drinks and foods more generally. Before I tell you the conclusion to the new story, it is useful to know the characters. Fortunately, there’s really only one.

A single species, Saccharomyces cerevisiaea, sometimes called brewer’s yeast, is responsible for nearly all fermented drinks, everywhere. This yeast-of-all-trades is found in the wild on tree trunks and fruits, though unpredictably and only here and there. Yet, from its rare germ grows a great feast. While the cow may give us milk and dogs give us protection and companionship, it is Saccharomyces cerevisiaea alone that gives us beer, wine, rice wine, fermented milk (not my favorite, either), sake, bread and much more.

In doing so, it might reasonably be in the running for the real title of “man’s best friend.” Yeast has the near miraculous ability to turn raw foods into delicacies. It does so by growing until, in each bite of bread or sip of wine, we savor the flavor of its body on our lips and feel it in our blood and head.

Brewer’s yeast is easy enough to cultivate. It grows on sugar, although “grows” is not really quite the right word. More accurately, it divides. One shimmering, blue-brown cell becomes two, two become four, and four — eventually — become billions. Brewer’s yeast prefers to live where it has oxygen, but it can also grow when and where there is little or even no oxygen. When humans make beer or wine, yeast is usually allowed to divide for hours or days until it is abundant. Then the conditions of the fermentation are changed to make it begin to live without oxygen, and as a consequence to produce ethanol — aka alcohol — and carbon dioxide as waste. For such waste we are grateful.

But how did a single species of yeast come to be used to produce so much in so many cultures? And, to return to Katz, did these events precipitate the need for agriculture?

In one version of the story, we might imagine that yeast is simply in the air, a kind of living ether that, when necessary, appears. The other version, equally if not more improbable, is that yeast has evolved with us, as a crop, much like wheat, corn or cows. If yeast has evolved with agriculture and our spread, its genes might also be able to tell part of our story as a kind of “bioglyph” rewritten with each act of yeast sex, division or mutational change.

The answer, or at least a big clue, was revealed when scientists decided to construct an evolutionary tree for yeast based on the genes of yeasts found in different foods. When they did, they were in for a surprise. The yeasts in beer, wine, sake and other fermented drinks and foods were different, very different, from each other. Those differences were ancient. Yeast does not just colonize any old food out of the hovering ether. It evolved and diversified as civilization and agriculture have evolved and diversified. Out of a few or even just one ancestral yeast strain, many new varieties have emerged. Just as from wolves came big dogs, small dogs, furry dogs and bald dogs, from one or a few yeast strains came all of the alcoholic flavors that we hold so dear.

Functionally, many of the differences among varieties of yeasts reflect their different lifestyles and roles. The yeast in ale beers is specially suited for the ways in which such beers are gardened. Because brewers tended to scoop yeast off of the top of beer (to later put in their next batch of beer), yeasts that ale brewers use tend to rise up out of the liquid they are in. They do this by clumping onto the carbon dioxide they produce, in order to catch a ride. In the wild, floating up and out of your food would be bad, but in beer it is vital to having your genes passed on. Malt beer yeasts also float, but they have extra copies of the genes associated with breaking down maltose, the main source of carbon in malt.

Similar (but different) stories emerge for wine. Many wine strains have evolved the ability to cope with high levels of sulfite, which has been used to clean wine containers since the Middle Ages. These sulfite-resistant yeasts have succeeded because they can pass from one batch of wine to the next without depending on a human to introduce them.

Bread yeasts, on the other hand, tend to be aggressive. They divide quickly, because we have tended to favor those bread yeasts that carbonate dough in the shortest amount of time possible. This fast action produces more odd flavors and so they have been (unconsciously) avoided in wines and beers. Bread yeasts have also lost the ability present in beer yeasts, and especially present in wine yeasts, to tolerate high alcohol concentrations. Put bread yeasts in with your grapes and they will die before they have produced much alcohol.

The new evolutionary tree tells us more than what the changes have been. It also begins to provide hints as to where and when those changes happened. Nearly all lineages of wine yeasts are related. They appear to have diverged early and, for example, all champagne yeasts appear most closely related to other champagne yeasts. Show me yeast, and I could probably tell you its region and wine variety. Sake yeasts share another old lineage, as are the yeasts associated with rice wine in China, fermented milk in Morocco, palm wine in West Africa or rum. Each of these lineages is the story of a drink, but also of a people and the accumulation of moments around campfires or on back porches sipping and discussing life.

Not all stories revealed by yeast genes are so simple. Bread yeasts appear to be different in different regions and have had different histories, a finding in line with the relatively late appearance of bread in archaeological sites. Sicilian bread yeast descended from wine yeasts. Other bread yeasts have other ancestors. These differences yield differences in tastes. Perhaps part of that un-capturable essence of Sicilian bread, for example, is a hint of ancient Merlot.

Then there is the story of lager beers and their yeasts, which evolved when Bavarians outlawed the summer brewing of beer. Winter brewing favored new hybrid yeasts able to live in the cold. These yeasts continue to give lager beers some of their unique flavors and are what made lagers possible in the first place.

Lagers exist because yeast was, relatively quickly, able to evolve, and evolution did not stop. Since that Bavarian law was originally passed, lager yeasts have diverged. The lineage associated with the Carlsberg breweries in Denmark and that in the Czech Republic differ from each other and from a third lineage found in the Netherlands.

In the end, yeast is ancient and telling. Its genes reveal the story not just of brewing but also of domestication. Yeast evolved as our tastes evolved. We had less control of the process of yeast domestication than that of, say, pigeons, and yet the resulting diversity of yeasts, a kind of evolutionary Galapagos from which we sip, is the product both of natural selection and civilization.

But we still need to return to the original question: Did beer lead to agriculture, as Katz suggested? Possibly. Beer yeasts evolved early. The evidence of beer gardening based on the yeast evolutionary tree is roughly as early as the evidence of wheat farming.

And so … maybe. What has become clear is that whether or not beer led to farming, yeast evolved hand in hand with agriculture nearly everywhere. Yeasts were there, holding, if not our hand, our cup. So it is that we have been drinking since the very beginning, from its prosperity. It is a prosperity that continues, a living cup that runneth over and will continue to do so as long as we are tempted by alcohol and bread.

And so remember the yeasts the next time you savor a cold one on the front porch with friends. Remember them when you break bread. Remember them, too, when you toast to, well … the evolution that flavors every sip and may have given rise to both bread and civilization, healthy food and beer.


For more about the stories of the wild species with which we interact, be they yeasts or tigers, read Rob Dunn’s new book, The Wild Life of Our Bodies.

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Rob Dunn
Rob Dunn is a science writer and biogeographer in the department of biology at North Carolina State University. His new book, The Wild Life of Our Bodies, explores how changes in our interactions with other species, be they forehead mites or tigers, have affected our health and well-being. Dunn lives in Raleigh, N.C., with his wife, two children — and more than two forehead mites (www.robrdunn.com)

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