Yeast, Co-Evolution, and Wasps
God made yeast . . . and loves fermentation just as dearly as he loves vegetation . . .
—Ralph Waldo Emerson, “New England Reformers,” 1844
The Georgian monk’s comment that God doesn’t make bad yeast reminded me of another facet of my wine ignorance. I’d never passed judgment on yeast because I never thought much about it at all. I knew that fermentation turns sugars into alcohol and carbon dioxide (thus the fizz in Champagne), and bread-making taught me that wild and commercial strains of yeast are different. But for me and most wine lovers yeast are kind of like bass players in rock bands—essential, but overlooked. So I had never asked the winemaking version of the chicken or the egg question. Are grapes responsible for all the marvelous flavors and aromas in wine—or is yeast? I’d always assumed the former, partly because wine labels, lists, and reviews rarely mention yeast type. Perhaps they should.
In 2016 the Australian Wine Research Institute gave an unusual tasting at a symposium in England. They offered five groups of sparkling wines, with three bottles in each set. At first glance, pretty normal. Each set was made at the same winery, from the same grapes, in the same style. The yeasts were the variable, and they were deliberately bred to produce distinctive flavors.
“It was quite striking how different these sparkling wines were,” Erika Szymanski told me in a phone call. She is a full-time scientist and part-time wine writer who works on yeast research. “You could definitely pick up that these yeasts had some distinctive aroma profiles. The room was quite polarized on whether we liked one yeast better or the other yeast better, but I think the universal agreement was, yes they’re different, and yes we like the hybrids.”
Master of Wine Sally Easton took part in the tasting, and her notes show how much the yeasts influenced the same original grape juice for a white wine:
Wine 4 . . . Smoke and aromatic tar on nose. Savoury, dry bread, hint bitter note, almond maybe, in a more positive frame.
Wine 5 . . . Floral, perfumed, almost muscat nose, repeated on palate. Gentle, lifted style, nice concentration of primary flavours.
Wine 6 . . .Wafty smoke, biscuit and brioche, more classic feel to this wine. Nice balanced dimensions. Wholesome.
One of the specially bred yeasts that Easton, Szymanski, and others liked is known as AWRI 2526. The Australian Wine Research Institute created it by mating a basic version of S. cerevisiae, the commercial wine yeast, with S. mikatae, a yeast not typically used for alcohol production. The S. mikatae was isolated from soil and decaying leaves. The Australians said the experiment created “a new breed of wine yeast” with the ability to increase flavor and aroma complexity, yet still deliver consistent production.
I asked Szymanski my chicken-or-egg yeast question—whether the grape variety or the yeast contributes the most to wine flavors and aromas. She got politely worked up, suggesting that A) it may be impossible to determine; and B) the question is way too simplistic. Her view is that humans and yeast co-evolved.
“When I talk about co-evolution, I’m talking about the ways that humans and yeast have developed closer than usual working relationships. It’s not just about a one-direction domestication of something. It’s about the way we interact, the way we respond to each other. We have developed long-term relationships that appear to be working well for the humans and the yeast,” she told me.
For example, bread yeast and wine yeast seem to have evolved differently. “It’s very important to note that of all of the communities of yeast associated with humans, wine strains are pretty robust, they’re pretty wild. They have to be very, very robust to deal with all of that alcohol and all of that sugar,” she said. But commercial bread yeast don’t survive particularly well in environments other than bread dough. That is, they seem to be almost dependent on humans.
Wine yeast have even adapted to our winemaking styles. More than two thousand years ago Egyptian, Greek, and Roman winemakers used sulfur (in the form of smoke) to disinfect clay amphoras. Spanish researchers found that about 50 percent of wine yeast strains contain a genetic mutation that makes them better able to resist sulfur. Wild yeast don’t have that mutation. Vineyards have also used copper-based sprays and dust for more than a hundred years. Originally known as “Bordeaux mixture,” it was applied in massive amounts to control mildews. As a result, some wine yeast have developed increased resistance to copper poisoning, too.
Yeast use our global wine-lust to travel, too. That’s significant because they’re not naturally airborne. DNA tests in New Zealand found that while some yeast came from local soils or oak trees, others matched the genome found in French oaks. While insects helped the local yeast spread and find niches in vineyards and wineries, the French varieties hitched a ride on imported barrels.
The travel evidence helps explain another puzzle. Scientists have noticed there isn’t much yeast on unripe grapes. Yet when the fruit ripens yeast is there—just at the point when grapes have their highest concentration of sugar, which is yeast food. Somehow, the yeast time their arrival. Birds are part of the answer, but some regions are still left with the question of frigid winters, which should kill local yeast off.
Some crafty S. cerevisiae found a solution in the guts and life cycles of wasps. Italian researchers captured and dissected nest-building wasps in the spring, summer, and fall. They found 393 yeast strains inside the insects. Some types rose and fell with the seasons, yet S. cerevisiae stayed fairly constant all year long. But how? The scientists isolated a small group of female wasps in the lab, inoculated them with a specific strain of S. cerevisiae, and let them hibernate. Three months later that yeast was still alive and well. The research showed that wasp queens can transmit yeast to young larvae and workers during the next life cycle. In the spring and summer they chew up food (mostly insects), regurgitate it, and feed their young. In other words, “wasps can maintain a potentially unending transmission of yeast strains through favorable and unfavorable seasons . . .”
The scientists don’t claim that wasp bellies are the only way yeast survive winter—they can live inside beehives, too. But they found that yeast strains in wasps and grapes from the same vineyard are very similar, even in different seasons and years. That suggests something I’d never suspected: not only does yeast play a role in creating distinctive regional wine flavors and aromas, wasps and other yeast-hosts are partners in the effort, too.
Other yeast research supports some theories McGovern and Vouillamoz have about the origins of winemaking. French researchers examined yeast DNA and found that most wine strains had a common parent region in ancient Mesopotamia—the Fertile Crescent. The wine yeasts spread across the Mediterranean and up the Danube River Valley, just like winemaking. The studies indicated that wine yeast and humans have had an intimate association for thousands of years. They also found that bread, beer, wine, and sake yeast diverged into groups—tribes, in a way—about ten to twelve thousand years ago. Each different yeast found a niche in a human industry, and mostly stayed there. The genus name, Saccharomyces, derives from the Greek words for sugar and fungus, and the species name, cerevisiae, comes from a Latin word for beer. Some ancient yeast DNA was also very similar genetically to strains McGovern isolated from Egyptian amphora.
Another team of researchers looked at modern yeast DNA, expecting to find a neat genetic trail leading back to a common ancestor. Hardly. It turned out that humans weren’t the only ones taking part in wine-fueled ancient orgies. The yeast cells hadn’t just split in two, which is how they normally reproduce. Perhaps helped by all the unwashed feet that smooshed grapes over the millennia, some had hooked up with different yeast species. So even within the general tribes of wine, beer, or bread yeast there’s some variety.
There’s still disagreement over where yeasts originated, and when. In the 1990s Raúl Cano, a professor emeritus at California Polytechnic State University, recovered S. cerevisiae DNA from the guts of 25-to-40-million-year-old bees and termites trapped in amber, and later from a Lebanese weevil that may have lived 125 million years ago. Fruits and other organic materials fermented long before humans showed up, so clearly yeast existed before wine. But for thousands of years no one really understood what yeast was, beyond some bubbling force that makes alcohol, bread, and fermented food such as pickles and kimchee.
By the early 1800s biologists began to realize that yeasts are separate, living organisms, which suggested that fermentation was more than a type of rot. Louis Pasteur began doing serious fermentation research in the 1850s, and he is generally credited with discovering the full role of yeast. Pasteur later wrote Études sur le vin, a four-hundred-plus-page survey of winemaking and vineyard diseases. It was the dawn of serious wine science.
Yet the idea of replacing wild wine yeasts with a commercially produced strain didn’t emerge until the 1890s, and that research languished for decades. Winemakers felt the tradition of using wild yeasts had worked for thousands of years, so why change? But change did come, in 1965, when a California winery used two dried yeast strains manufactured by Red Star Yeast. By the eighties many large wineries used commercial yeast for some or all of their winemaking. At first glance, so what?
All the research suggests there was once a huge diversity among wild yeasts and even regional wine grape yeasts, but there’s a problem. Commercial wine yeasts are taking over, literally driving some of the wild populations towards extinction. Researchers sampled yeast populations in a new Spanish winery for five years. At first local non–S. cerevisiae strains dominated the first stage of fermentations. But over time the commercial yeast pushed out the local ones. Other researchers found that while there are hundreds of different commercial wine yeast products, many of them are virtually identical genetically.
I saw parallels to Wine Grapes, though I doubt there’s the same market for a thousand-plus-page companion called Wine Yeasts (though one never knows). In any case, yeast clearly affect wine flavor, and their diversity is threatened, too.
A quirky twist left me hopeful and puzzled. Cano, the scientist who extracted the multimillion-year-old yeast from amber, tried to patent the primordial organisms. He originally thought they would prove useful or profitable in biotechnology or medicine. That didn’t work out, but he cultured some of the yeast spores and realized they could make a beer.
In 2008 Cano started offering trial batches of Fossil Fuel brew, and in 2016 he continued the experiment with Schubros Brewery. An Oakland Tribune critic said the yeast gave the wheat beer a distinctively “clove-y” taste and a “weird spiciness at the finish,” while the Washington Post deemed it “smooth and spicy, excellent with chicken strips.” After the brief burst of publicity, though, the project seemed to disappear. Schubros brewer Ian Schuster told the San Francisco Gate the yeast was unpredictable and “high maintenance,” prone to delivering different tastes at different temperatures. “It needs to be roused,” he added somewhat mysteriously.
I found some possible explanations in other scientific papers, which suggested that the primordial DNA was impure, or degraded. Or perhaps it was a glimpse of the distant past when even yeast was “finding its way,” so to speak, learning how to best transform sugars into alcohol and carbon dioxide. As a business venture the ancient yeast may just be too finicky to deliver any consistent flavor, which is a big problem.
The Fossil Fuels experiment illustrates a bigger point. There are still a lot of questions about how yeasts do their fermentation magic. Clayton Cone, a scientist with Lallemand, a French company that specializes in food yeasts, said in a recent article that even he has “only a rudimentary understanding of what is going on inside the yeast cell.” What’s clear, however, is that over millions of years countless yeast species adapted to highly specific environments—including within grapes, wine barrels, or other winery equipment.
The US Food and Drug Administration approved a genetically modified (GM) wine yeast in 2003. So far it hasn’t led to huge controversy, perhaps because the FDA doesn’t require winemakers to tell consumers whether it’s used, since yeast are technically processing agents and not ingredients. The GM strain is now marketed by Lesaffre, a French food science company with roots that go back to 1853.
The GM yeast was approved for use in the United States, Canada, and South Africa, so many people have probably already drunk wines made with it. A closer look at the new yeast shows how alluring such products might be for producers. The technical details are that it allows so-called secondary, or malolactic, fermentation to take place during the traditional first fermentation, saving time and perhaps making quality control easier for the winemaker. The yeast’s creator said it can eliminate by-products in wine that produce off-flavors, and perhaps even those which lead to headaches or other negative health effects. (There’s no proof of those last claims, by the way.)
Szymanski wrote in a blog post that humans may not make the best long-term choices for the yeasts or for flavors. “[O]nly yeast with mutations that do something we like will be picked up and propagated en masse instead of being weeded out as undesirable. This probably doesn’t bother you. Unless you, like me, stay up at night worrying about microbial genetic diversity . . . But what if we’re letting the strongest persuade us to act in their favor at the expense of listening to all of the voices involved or considering long-term environmental policy?”
In other words, what if the oddball yeast play important roles in vineyard ecosystems? That’s another way of suggesting the Georgian monk was right. In the big picture there are no bad yeasts.