Go Yeast, Young Man!

This Versatile Micro-Fungus Can Be a Winemaker’s Best Friend

    Those little critters we call yeast are very important to some of mankind’s greatest achievements: They are integral to wine, bread, pizza, beer, spirits and medicines. (They also give us the occasional infection, although that’s not necessarily a great achievement.) In the wine business, we use many different strains of yeast, and they can be our best friends—or our worst enemies. Most yeast metabolizes carbohydrates, such as grape or grain sugars; the process produces carbon dioxide and alcohol, mostly in the ethyl form, which is what we consume in wine and spirits.
    Some strains of yeast, however, actually metabolize alcohol, giving off some very strong-smelling products called 4-ethyl phenol, and 4-ethyl guaiacol that show up in wine as a dirty barnyard character. A particularly troublesome form of this yeast is called Brettanomyces. It is present in many wine cellars and is unaffectionately known among winemakers as “Brett” or “the B word.” In small amounts, around 300 parts per million, these products can add some complexity to the flavors of wine, particularly Cabernet Sauvignon and Pinot Noir, and interestingly, they are almost never found in white wine. When we hit levels of 700 to 800 parts per million, it makes the wine taste sort of like a combination of dirt and liqui d cow manure.
    Some wineries would have you believe that these characteristics are due to terroir, which means that the wine is influenced by the soil, climate and general surroundings where the grapes were grown. Unfortunately, it’s the terroir of their wine cellar that is infected with Brett, which is very hard
to eradicate.
    On a more positive note, there are now hundreds of strains of yeast that add interesting and unique qualities not only to wine but also to beer and spirits. Most originally occurred naturally in the vineyard and have been cultured and isolated from various wine regions, evolving over centuries of grape growing. For white wines we may use a yeast called Epernay, which was isolated from near the town of Epernay in the Champagne region of France; for a big red wine we might use a yeast called Syrah, originally from France’s Rhone Valley, which is the heartland of the Syrah grape. The outcome is a very hearty and rich red wine with lots of exotic fruit in the bouquet.
    Yeast’s natural occurrence in nature, and in the vineyard, probably explains how fermented beverages such as wine and beer were discovered by ancient man. Imagine a cave guy who gathers some ripe wild grapes and puts them in a stone bowl while he’s off on a week’s hunting trip. As he drags a warthog back into his cave for dinner, he’s met by this great smell of freshly fermented grape juice. Hopefully he had some friends to invite to the feast.
    Many winemakers like to use natural fermentation, rather than adding yeast to the vat. This can create some pleasant complexities in the wine, but it can also result in off odors and stuck fermentations. Research has shown that it takes 22 to 24 individual strains of yeast to complete a fermentation that brings a 24 percent sugar level down to zero. One strain will be dominant in the process from 24 percent to 22 percent, another strain will dominate down to 20 percent, and then it passes the baton to the next strain until all the food (sugar) is gone.
    Occasionally, wineries will find one dominant yeast responsible for a great natural fermentation. This is the type of organism worth isolating and culturing to produce a proprietary fermentation tool that adds specific flavors and textures to the wine. There are laboratories that specialize in this kind of work and produce commercial strains of yeast available to everyone. At Rosenblum Cellars we have isolated two yeasts that we feel are special and unique in that they not only produce great fruit-driven bouquets but also work well in many environments, from cold to hot, and at low or high alcohol levels. Both of these come from mountain Zinfandel vineyards located in Sonoma County. One is from the more-than-100-year-old vineyard called Monte Rosso, located in Sonoma Valley, and one from the Rockpile Vineyard above the Dry Creek appellation. These two yeasts now account for 40 percent of our total red wine fermentations.
    Yeast experimentations and isolations will continue at a faster pace all over the world and continue to improve everything from wine to bread. Who knows, maybe we’ll even find one in Saudi Arabia that we can call the Middle Yeast.

—By Kent Rosenblum

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