Issue link: http://read.dmtmag.com/i/138003
SOILCOHEN & CELLAR REMI Go Native …Or Not? Factors to consider when choosing a yeast native, or indigenous, fermentation occurs when yeast is already present in the must, in contrast to fermentations that occur by inoculating the must with yeast, usually a strain or strains of Saccharomyces cerevisiae. The yeast present in the must of a native fermentation can originate in the vineyard, the winery, or both. Proponents of native fermentation tend to like the idea that it is a more natural winemaking process, and they also believe that more complexity is gained in the aromatic profile. A wine's aroma results from compounds that are present in the grapes, or are generated through the processes of fermentation and aging. Grape aroma compounds are present as free volatile compounds or as bound sugar conjugates, which are nonvolatile aroma precursors that contribute to aroma once they have undergone acid or enzyme hydrolysis. Research has shown that yeast strains vary in their production of volatile aromatic esters and glycerol, and also in the conversion rate of sugars into ethanol, all of which can impact the flavor, mouthfeel and chemistry of a wine. Many yeast genera and species, including Saccharomyces cerevisiae, have glycosidase enzymes, which can affect wine aroma by hydrolyzing aromatic precursors, the bound sugar conjugates, found in grapes. However, there is debate among scientists as to how much this glycosidase activity varies among yeast strains. Some research has shown similar levels of glycosidase activity, and overall low activity of these enzymes in wine, yet w w w. v w m media.com most studies point to native fermentations showing different glycosidase activity than fermentations inoculated with commercial strains of yeast. MYRIAD SPECIES Many different genera and species of yeast have been found on grapes and in wineries, and the composition is influenced by geography, vine age, variety, seasonal variations, farming and harvest methods, as well as winemaking and sanitation techniques in the winery. Frequently isolated species include Hanseniaspora uvarum, Kloeckera apiculata, Metschnickowa pulcherrima, Candida pulcherrima, Candida stellata, Pichia membranaefaciens, Hansenula anomala, Torulasporadelbrueckii and Kluyveromyces thermotolerans, as well as Cryptococcus, + A native, or indigenous, Rhodotorula and Sacchafermentation occurs when romyces species. yeast present in the must Although numerconduct the fermentation. ous yeasts may start an uninoculated fer+ Native fermentations can mentation, most of add complexity to a wine the strains are not due to variability in yeast as alcohol-tolerant strains' generation of aroas Saccharomyces spematic compounds. cies, and over the course + Proponents of native ferof most fermentations, mentation may want to other yeasts decline and inoculate, depending on the indigenous strains of Saccondition of the fruit and charomyces establish, and the facility in which they are winemakers hope, comworking. plete the fermentation. Often, numerous Saccharomyces strains are pres- AT A GLANCE J u l y - A u g 2 0 13 | V I N E YA R D & W I N E RY M A N A G E M E N T 33