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Ask a beer brewer or a bread baker where to find wild yeast and they'll tell you everywhere.
It's in flowers, in trees, on fruit, in vegetables, in beards, further south, and all throughout our homes and neighborhoods. Every time you touch anything, you probably are picking up and putting down yeast. (Are you picking up what I'm putting down?)
Wild yeast is everywhere, and it's essential to achieving tangy sourdoughs and tart, fruity beers (not to mention wines and cheeses and many more things—but for brevity, this article will focus on the former two). But what is it, and why is it different than the stuff you dump out of a packet and into a mixing bowl when you're making challah?
If we're going to talk about wild yeast, we should first talk about the yeast you use in your challah: That yeast is "domesticated," the strain cultured for the mild, yeasty properties we love in bread. It's what we think of when we think of something as yeasty-smelling, and it's so common that we know it simply as baker's yeast, though it has an official name, too—Saccharomyces cerevisiae. While you can, of course, use baker's yeast to make bread, that bread won't have the complexity of flavor or texture that sourdough does (though using baker's yeast is generally a lot faster than other routes, and you don't have to nurture a starter); and you can't make beer with the packets you buy at the grocery store.
But you can make beer with Saccharomyces (a.k.a. "Sacch," a.k.a. brewer's yeast). In fact, it's the yeast most commonly found in beer. "Saccharomyces makes about 99.9% of beer in the world," Anthony Accardi, a brewer at Transmitter Brewing in Long Island City, Queens, told me. He's exaggerating a little, but not much: Saccharomyces is used to make both ales and lagers, the world's most popular varieties of beers and the buckets into which you can classify almost all beers. (Some refer to strains of Sacch as "lager yeast" or "ale yeast.") Saccharomyces, for reliability, availability, efficiency, and ease, is king among yeasts in beer making and bread making alike.
But the funkier among brewers and bakers turn to wild yeasts for experimentation and many delicious (and curious) results. Wild yeast is beloved for its funkiness—it is wild, after all. Or, mostly wild: When you ask about wild yeast, what someone with yeast on the brain (especially a brewer) most likely hears is "Brettanomyces," another common species of yeast and perhaps the most common after Saccharomyces. Brettanomyces, or "Brett," is indeed all around us (hence, "wild") but it's also widely available for purchase; there are dozens of Brett strains you can buy. Its wild reputation is largely a result of it not being Sacch (which, for the record, can and does also occur in the wild).
But its flavors are wilder, too. Whereas Sacch goes hard on familiar bready, yeasty flavors, Brett skews both brightly fruity—pineapple, clove, banana—and funky, like hay or "horse blanket," John Lapolla, owner of the Brooklyn home-brewing shop Bitter and Esters, explained to me. (Anthony identified it as "sweaty sock.") You might not think of those things as going well together, and sometimes they don't. There's a lot of experimenting required. But lambics and geuzes, both sour beers, owe their punchiness to Brett.
Many Belgian beers (like lambics and geuzes) are brewed with and characterized by Brett. Anthony calls Belgian beers "yeast-forward" (as opposed to "hop-forward," like many American beers, or malt-forward German ones)—and this comes from a long Belgian tradition of brewing with wild yeast—often spontaneously. Some American brewers experiment with spontaneous fermentation, too: John told me that you can do this by setting your wort (the "starter" of beer, a sort of sweet solution that you add yeast to) under a tree—especially a fruit tree, since one of yeast's favorite places to hang out is on sweet fruit—cover it with a cheesecloth to keep anything larger than yeast out, and wait. (Anthony said that some will simply put a flower into their wort and hope that the yeasts living on the flower are tasty ones.) Hungry, wild yeasts find their way into the wort, feast on the sugars in it, and create carbon dioxide and alcohol. This is the beginnings of beer.
More: Learn to brew one of John Lapolla's beers, the Bitters and Esters Disaster IPA.
Or bread. The same process takes place when you leave a solution of flour and water—the beginnings of a sourdough starter—on your kitchen counter. Just as with the wort, the ambient yeasts and bacteria in your kitchen seek out the sugar in the starter, and the rest is history. Is your sourdough starter bubbling? Yeast has paid a visit.
Sam Fromartz, author of In Search of The Perfect Loaf and sourdough enthusiast, reminds two things: First, he told me, yeast isn't the only player responsible for how your loaf (or your beer) tastes: Bacteria is its partner in crime, and the two "essentially are creating compounds that help the other to grow. Wild yeasts favor a more acidic environment," and bacteria creates acids (lactic acid, which contributes a yogurty tang, and acetic acid, which is more vinegary) as byproducts. Secondly, it's "a misnomer that yeast is just floating around in the air"; it needs "some sort of surface or agent to live in or on"—like your wort or starter or fruit basket. But the more you bake, the more likely it is there's a steady population of yeast in your kitchen, Sam said. The cocktail of bacteria and yeast in your sourdough starter or beer wort will be unique to you and your kitchen; think of it as your own personal terroir. This is one reason Transmitter Brewing doesn't do much spontaneous fermentation; in the middle of New York City, their beer would taste like "tire fire," Anthony said. Or worse.
But that terroir expresses itself in a multitude of ways is exactly why bakers and brewers find working with Brett and other wild yeasts so exciting. "Wild yeast can produce strong flavors that can be surprising or off-putting," Anthony said, but the "ability to make a wide range of flavors is really appealing. Once you get over the hurdle, you can make beverages that are truly layered and nuanced, revealing subtle flavors that might not be possible otherwise." This is true of both beer (think of the face-twisting-est sour you've ever sipped) and of bread (with its satisfying, dairy-ish tang and chewy crumb).
More: Sam Fromartz says a happy starter starts with whole rye flour and raw honey. Make his recipe.
- 8- or 16-ounce plastic or ceramic container with lid
- Organic whole rye flour
- Raw honey
- Filtered or spring water (so bacteria-killing chlorine is removed)
If wild yeast is so great, why isn't it the norm? Why aren't more brewers doing spontaneous fermentation? It mostly comes down to inconsistency of results: Because spontaneous fermentation doesn't leave much control in the hands of the brewer, it's hard to reproduce results—so it's hard to keep going once you've found a flavor you really love, and hard to not make the same mistakes twice. This is why you can buy Brett cultures, and why Sacch has risen to popularity in brewing and baking alike: It produces really consistent results. Wild fermentation thrives in bread baking, but it is a more time-consuming process than simply dumping a packet of yeast into a bowl. And it's funkiness, though beloved by some, does limit its appeal to a wider market. But it's certainly worth experimenting with.
What's your own yeast experience (and preference!) in bread making and beer making? Are you more of a Sacch or a Brett? Tell us in the comments.