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April 2016 WINES&VINES 83 WINE EAST WINEMAKING tations, always was assumed to move into must from the waxy cuticle coating grapes. More recently, studies have shown that S. cerevisiae is rare on healthy fruit and can be isolated from just one per 1,000 undamaged berries. Indig- enous vineyard yeast are more commonly non- Saccharomyces species, including Kloeckera apiculata/Hanseniaspora uvarum, Candida, Cryptococcus, Debaryomyces, Hansenula, Is- satchenkia, Kluyveromyces, Metschnikowia, Pi- chia and Rhodotorula. When S. cerevisiae strains have been identi- fied in vineyards, they are often commercial strains that have been used in wineries associ- ated with the site. In effect, commercial strains take up residence in the winery and migrate outward, populating the vineyard in numbers somewhat proportional to the distance traveled from the winery. This is not surprising, as 95% of strains associated with wine production have been found to share a unique common ances- try, suggesting that yeasts adapted to winemak- ing developed and spread with human activity. In other words, though there is evidence for region-specific subpopulations in vineyards with a long history of wine production, they are likely the result of localized gene flow be- tween regional wild yeast and strains that evolved in the early days of wine production and were spread by humans. A recent study in Missouri provided evidence that genetic information was exchanged be- tween members of the so-called "grape/wine" S. cerevisiae population common to winemaking areas and the indigenous regional population that thrives on oak trees. These "wild" oak tree strains are generally unable to survive the levels of SO 2 and alcohol that occur in wine fermenta- tion. In theory, such merging of "grape/wine" and "oak tree" populations could result in the development of yeast strains in the vineyard that retain some wild characteristics but are capable of successful fermentation. On the whole, however, there is little evidence that a population of wine-ready yeasts is lurking in every corner of the globe, just waiting for a "natural" winemaker to give it a fermentation of its own. It is probable that wine yeast are more similar to domesticated dogs that share a com- mon ancestor but have evolved to display breed differences based on regional work conditions. Yeast in the winery Several researchers have argued that the winery, rather than the vineyard, is the primary source of S. cerevisiae in spontaneous fermentations. In some studies they have been found to com- pletely displace any yeast strains originating in the vineyard. The concept of "resident micro- flora" in the winery has been described fre- quently, and in many cases commercial yeasts have been found to adapt to winery conditions and colonize equipment for several years, even surviving typical cleaning methods. If present, these yeast strains are often the most competitive in a given fermentation and have been found to coexist with other strains or take over spontaneous fermentations in the facility. It's important to remember, however, that yeast reproduces rapidly and readily ac- cepts genetic material, so that resident winery yeast often show genetic variance from their commercial strain of origin and may naturally evolve enough over time to show significant difference in activity and, consequently, wine sensory characteristics. Sensory impact of mixed cultures Whether spontaneous fermentations are a pure expression of vineyard micro-terroir or simply a history of previous yeasts used in a winery, there is no doubt that their varying microbial popula- tions produce a unique assortment of wine aro- mas and flavors. Most microorganisms have lower tolerance for SO 2 , CO 2 and alcohol than commercial yeast cultures, so typical inoculation methods that include post-crush SO 2 treatment and pitching with robust commercial yeast se- verely limit the number of players that can live, die and contribute secondary metabolites (aroma 251 Gambee Road, Geneva, NY 14456 Phone: 315-759-2118 Toll free: 888-234-6752 Fax: 315-789-1848 Email: cjennings@vancemetal.com Website: www.vancemetal.com Quality Rugged 12 gauge, Custom & Stock Stainless Tanks Catwalk Systems • Pump Over Carts • Custom Hoppers, Chutes & Bins PROUDLY MADE IN THE USA