I have a confession to make publicly. I am a Yeast Wrangler. In every fermentation, every harvest, I try to get inside the minds of these tiny fungi and discern what they want to eat, how they would like to be treated, and what temperature they would like their environment to be. They make the wine and winemakers try to keep them happy. They are like the ultimate prima donna who refuses to work unless everything in their environment is to their liking. If something is out of place, they immediately let you know by sending off Hydrogen Sulfide (H2S), which smells like rotten eggs, to voice their displeasure. If their needs are still not met they will shut down and die off resulting in a stuck fermentation. If one considers that winemaking is the physical act of converting sugar into alcohol and Carbon Dioxide (CO2), then I am a yeast wrangler and they are the winemakers.
In light of this, the selection of the strain of yeast or yeasts that will be conducting the fermentation is critical. Next to the date of harvest, it is one of the most impactful decisions a winemaker will make over the course of a wine’s life. Yeast can control alcohol levels, fruit emphasis, and style. They can also influence mouthfeel, acid levels, and Malolactic (ML) bacteria growth. Much of the later part of the life of a wine can be enhanced or hindered by the choice of yeast at the beginning. To that end, there are nearly endless choices available to a winemaker to choose for fermentation including “native”, selected or cultured strains, and a few options in between.
Using the indigenous yeasts found in the vineyard and winery can be a double edged sword. On the positive side, they can add serious complexity and mouthfeel to a wine. They already exist in the winery therefore they don’t have to be purchased, which is helpful since the cultured strains can be pretty expensive. The downsides are they can be very difficult if the native strain is not a strong one, if the fruit is not perfect, if the nutrients they need are not carefully doled out, if the potential alcohol is too high, and if there are other yeast or bacteria strains in the fermentation which the dominant native strain does not get along with. These risks can be mitigated if one knows the reactions of their native strains well and knows their vineyards well also. There are now many examples on the market of excellent native fermentations including the Franciscan Cuvée Sauvage Napa Valley Chardonnay and all the selections of the delicious Bedrock Wine Company in Sonoma, CA. It should be pointed out here however that most “native” strains are the strain of yeast a winemaker may have purchased in a previous year that has still been hanging out in the winery or which dropped in from a cultured yeast fermentation from a neighboring tank.
Seeking Some Culture
Cultured yeasts are extremely widely used and many strains which we would consider cultured now were isolated as native strains from different places around the world. One of my personal favorite cultured Pinot Noir yeasts is RC212 which was isolated in Burgundy and named for the famed Romanée-Conti vineyard. Cultured yeasts offer some insurance against stuck fermentations due to high alcohol and have known characteristics such as nutrient needs, foaming potential, or H2S production so a winemaker is better able to keep them happy from the start of the fermentation to the finish. Beyond that, some cultured yeasts are bred for specific characteristics such as high Thiol production (think guava and grapefruit flavors of New Zealand Sauvignon Blanc), alcohol tolerance of 16% or higher, or high polysaccharide production which adds to mouthfeel and tannin perception. If you have enjoyed a glass of wine from a larger producer chances are good that it was produced using some strain of cultured yeast.
Best of Both Worlds
Of course, in winemaking as in life, things are not always black and white. Sometimes a winemaker wants the complexity and character of a native fermentation but the predictability of a cultured strain. This can be achieved through two main ways. The first option is to allow “native” yeasts to start the fermentation and then part way through add a smaller dose of a cultured strain to ensure that the fermentation will finish. The second option is to purchase a mixed strain such as Viniflora’s Melody which is a 60:20:20 blend of Saccharomyces cerevisiae, Kluyveromyces thermotolerans, and Torulaspora delbrueckii. These mixes theoretically mimic what would be found in a native fermentation except the strains are chosen that will complement each other. This ensures the different strains will not end up in the yeast version of Gladiator, with no single strain winning the fight to the death.
Regardless of the yeast option chosen it is critical that those strains remain happy and healthy throughout the fermentation and that is where the yeast wrangling part of a winemaker’s job comes into play. They have similar needs and, while some require more coaxing than others, both can adequately do the job if all those needs are met. It is harvest time now in the Northern hemisphere so for the next two months anyway you can find me roping fermentations into line and figuring out what each tank of yeast wants.
Originally Written for and Published on Snooth.com on 9/17/2015