Recently while in Paso I had an interesting and enlightening conversation with David Parrish of Parrish Family Vineyards regarding yeast.  Now this is not a subject that I have in depth knowledge on, most of what I know I have picked up by listening at my favorite vineyards.  I walked into the conversation a big supporter of the use of natural yeast, without any real understanding of why you wouldn’t use natural yeast.  David explained that natural yeast could be a completely uncontrollable variable in wine making.  This was a new perspective for me.   So, today is the day to research and explore the pros and cons of indigenous yeast vs. adding cultured yeast to wines.

First, I suppose we should talk about what part the yeast plays in the making of wine.

Yeast is what causes the fermentation process in wine.  The yeast, just like when you are making bread, eats up the sugars and produces, in this case alcohol and carbon dioxide.  The yeast will typically continue to do this until it has transformed all the sugars. The process can stop or be stopped short of that, which gives you the residual sugar in wine.

Indigenous yeasts are those that are “naturally” occurring in the vineyard or winery.  Yes “naturally” is in quotes, because well…yeasts can show up from anywhere.  Lets begin by talking about the natural yeast that you find in the vineyard.   In Europe these yeasts that are found on the skins of the grapes are considered part of the terroir.   Often called the “bloom” or “blush” these yeasts can be seen on the skin of the grape and come into the winery with the grape during harvest.  These native yeasts can produce amazing and unique wines, but they are also a bit of a wildcard, because they can also be unpredictable causing off flavors or aromas and possible spoilage.  Wild yeast as it is already on the grapes can start the fermentation process immediately, as the weight of the grapes on top crush the grapes on the bottom the yeasts can go to work before they even get to the crushpad.  Indigenous yeast can take longer to get going with fermentation and there isn’t a specific formula for how long fermentation will take, so the winemaker must be vigilant, checking in on the process often to see where it’s at.  The type of vineyard can assist natural yeast in the vineyards.  If the pH is low and there is high acidity this will help the yeast to succeed.  Often warmer regions with higher yields don’t work as well for natural yeast.  The variety of natural yeast found in a vineyard can also add to the diversity of flavor in the wines.  In Europe most wineries use natural yeast, this is the way it has been done for centuries.  Often a “pied du cuvee” is used to kick start a slow fermentation.   A “pied du Cuvee” is like sourdough starter.  Grapes are picked a few days or weeks prior to harvest and crushed to cultivate the yeasts.  Then if the fermentation from the indigenous yeasts is slow this can be added to kick start the fermentation process.  This is also used if there is rain before harvest that washes away many of the natural yeasts on the grapes.

On the downside, it has been said that the benefits to flavor of natural yeast can only be shown while the wine is young, after 6 months of aging these notes are no longer noticeable.  And…yeasts also can be found in the winery and cellar and these are thrown into the mix along with any that arrive on equipment coming into the winery, so you have additional curve balls that can be thrown in.  Also many indigenous yeast are of strains that only tolerate low alcohol levels, once levels reach 3 to 4% these yeasts die off.

For the winemaker who prefers cultured yeast it is all about control.  Yeast is an ingredient carefully chosen for a specific effect. I mentioned how indigenous yeast can be a wild card?… Using indigenous yeast it is possible to lose 10-20% of a wineries wine if the yeast does not behave in the way you expected.  Many small wineries do not want to take that chance.  And…well once you use a cultured yeast, that powerhouse of a yeast is in your winery and will overpower any native yeast that comes in, so it’s hard to go back.  Cultured yeasts will start the fermentation process much more quickly.  Large producers use this to quickly ferment, so they can move on and reuse the tanks.  Cultured yeasts are primarily “sugar yeasts” and there are several hundred strains to choose from.  The type of yeast can affect the characteristics of the wine even changing characteristics within a grape variety.  Some strains make a heavier sediment to make it easier to rack the wine.  Commonly with added yeast a large dose of a single strain is added to start the fermentation process.  Saccharomyces cerevisiae is the primary yeast used in fermenting wines.  Unlike many naturally occurring types of yeasts it can tolerate high alcohol levels.

There are downsides to using cultured yeast.  You can have problems with volatile acidity and stuck fermentations, problems you don’t see with natural yeast.

My summary:  This is just the start of my research on yeasts.  I look forward to conversations with winemakers on their opinions.  I am all about the love of wine, and the winemaker’s love of winemaking.  The romance and history of natural yeast and my immense love of Tablas Creek has me leaning in that direction.  But…as I have said before gorgeous wine comes in many forms.  There are so many variables in wine, in the growing of the grapes, in the harvesting, in the winemaking… and I enjoy wines with many different backgrounds and styles.  We discussed Biodynamics and Organically Certified wineries before.  Do those labels make these wineries and their wines better?  No, but often it means that the winery and winemaker are passionate about their wines and are striving to find ways to make them better.

So here’s to the discussion and exploration of winemaking in all it’s many forms and facets!  Cheers!