From Thin Air
Though people often reference yeast strains as being “brewer’s yeast” or “bread yeast” or “wine yeast,” the actual distinctions between these categories aren’t always as cut-and-dry as the titles suggest. Many bread yeasts can be used to ferment beer. Belgian strains tend to exhibit closer similarities to wine yeast than conventional brewer’s yeast (both in terms of size and phenolic byproducts). The majority of the types fall into the Saccharomyces cerevisiae species. In the end, the categories generally serve to indicate that a particular strain will get the job done.
Encountering an unfamiliar yeast strain, one feeds it some malt sugars and hopes for the best.
Back in 2010, Dogfish Head’s Sam Calagione and company traveled to Egypt with the hopes of being able to capture a local strain of wild yeast for their recreation of an ancient Egyptian beer. The team set a few dozen petri dishes and swingtop bottles outside (after visiting the Tomb of Ti, famous for its hieroglyphs depicting the related processes of beer and bread making), fitted with local juices and dates and—most importantly—isoamyl acetate. Isoamyl acetate, better known as the banana note produced by German hefeweizen yeasts, also serves to attract the pitter-patter of fruit flies’ yeast-laden feet.
By collecting, isolating, and propagating some of the various wild yeasts that happened into their “yeast traps,” the Dogfish Head team was able to pick out an as-yet-unidentified Saccharomyces strain that could ferment their Egyptian ingredients favorably. In 2011, back home, they collaborated with the University of Delaware to repeat the process at a nearby peach farm, isolating “a wild Delawarean yeast” to ferment their locally sourced beer, D.N.A. (aka “Delaware Native Ale”).
At the 2011 Craft Brewers Conference in San Francisco, Calagione encouraged other brewers to attempt similar projects. “We really see this opportunity to locally source and grow yeast, for each of us wherever we live, as a great frontier that has not been fully explored yet by the craft brewing community.” He later added, “Unlike the wine world, a lot of our terroir is just in the air, not under the soil.” Two questions are quick to arise, though: how hard is it to do this sort of thing, and how likely is it one will end up finding something useful (and tasty)?