When to harvest and how to harvest that is the question.
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. Read More