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winemaking 82 Wines&Vines January 2015 I n an effort to find what microbes might be affecting com- mercial wineries, professor David Mills from the Univer- sity of California, Davis, swabbed locations all over the UC Davis research winery before and after harvest. His findings included a large number of microorganisms—some unfamiliar to most winemakers, and others that are identi- fied with toxic microbes (though not the strains found). Mills revealed his discovery during a session about "wild" yeast strains at Rootstock, a Napa Valley Grapegrowers conference and exhibition held in Napa, Calif. (See "Napa Grapegrowers Consolidate Events" on page 162.) The session also examined the role of what could be called feral yeasts (cultured yeasts that have gone wild). Researchers at the UC Davis research winery found Sac- charomyces yeast around the garage-sized door used to bring in grapes—even before there were grapes in the winery. Mills also found Brettanomyces in a stainless tank. It turns out the tank had been used for work involving that yeast a year before, and it had been thoroughly cleaned after use. The researchers are trying to determine how the mi- crobes got into and moved around the winery. Some pos- sibilities include humans, equipment and insects, notably the fruit fly Drosophilia. The latter turned out to mostly spread Saccharomyces and other yeasts, not acetic acid and lactic acid bacteria as commonly thought. Quick and cheap identification Mills noted that traditional methods of identifying yeasts and other microbes are tedious and time consuming, but recent developments using new technology including paral- lel computing have made enormous progress in the past decade. He said that it's even outpacing computer storage, a notoriously fast-moving field. "We're having trouble stor- ing the results," he complained. Mills added that in his early days, it took $1.6 million to sequence lactic acid bacteria. Now he can map 50 mi- crobes for less than $1,000, and much more quickly. This allows researchers to take more samples, and he noted that adequate work could require more than 300 samples. The research also led them to various regions of the world, where they found different yeast and bacteria pro- files. Even different regions of the relatively small Napa Valley exhibit diversity, leading many researchers to specu- late whether this might have something to do with the reali- ties of terroir, the concept that every winegrowing region produces a distinct wine. Saccharomyces domestication Lucy Joseph, who manages the yeast collection for the UC Davis Department of Viticulture & Enology, discussed how Saccharomyces comes to dominate wine production. Saccharomyces is fairly rare in sound berries in the vine- yard, and it is found in about one of 1,000 berries tested. This is partly because the yeast is very sensitive to ultraviolet light. However, the concentration is much higher in dam- aged berries (about one in four berries tested). The number of Saccharomyces cells on damaged berries is about 10 4 to 10 5 cfu/ml (colony forming units), but the total microbial counts in damaged berries is much higher: 10 6 to 10 7 cfu/ml. The yeasts in vineyards seem to come primarily from trees that were previously in the vineyard or surrounding it, but Joseph says that the wild yeasts apparently haven't been studied extensively. Those yeasts found in wineries can get there from many sources including the grapes, surrounding environment, equipment (especially barrels) and, of course, introduced cultured yeasts. Wine yeasts originate primarily from Eu- rope with other yeasts found throughout the world (like sake yeasts in Asia). Only the strong survive So why do Saccharomyces yeasts come to dominate wine fermentation? It occurs partly due to natural selection favoring Sac- charomyces like low pH, high sugar concentration, some nutrients like nitrogen, high phenolic content, low oxygen and alcohol concentration. In addition, winemakers encourage Saccharomyces through raising temperature, adding potassium metabisul- fite, lowering pH with tartaric acid and adding lysozyme and nutrients. One result is that non-Saccharomyces yeasts start out strong but are discouraged by rising temperatures and al- cohol levels (ideal conditions for Saccharomyces). Role of Yeast in Winemaking Experts discuss wild, feral and cultured yeasts at Napa Valley Grapegrowers' event By Paul Franson CeliaCarey.Com Film & PhotograPhy Attendees sampled wines inoculated with both wild and cultivated yeast strains.