Vineyard Journal, October 2021: Fermentation
Last month was harvest. Let’s give our weary vineyards a break and follow the fruit inside.
Spontaneous fermentation has to be one of the most thrilling moments in gastronomy. When grapes are crushed, the wild yeasts living on them get to work eating the sugar in their newly accessible juice, producing alcohol and carbon dioxide as waste products in a process called primary fermentation. Different yeast strains grow on different varietals in different regions and may contribute unique flavor to their wines.
Sometimes spontaneous primary fermentation takes longer to begin than we’d like. While we wait for the yeasts to hit their stride, opportunistic microbes can produce off-flavors before they’re wiped out by clean, alcohol producing saccharomyces. To prevent this, some farmers encourage native yeast fermentation in two steps with a technique called pied de cuve: a bucket of grapes is crushed a few days in advance, then added to harvest’s freshly crushed juice at a roiling ferment. This way, fermentation starts in the main lot right away, and any off-flavor compounds produced in the bucket get diluted into obscurity.
Still other good farmers hedge their bets and inoculate harvest with neutral, cultured saccharomyces to convert sugars into alcohol efficiently for the same reason as the pied de cuve crew: so the flavor grown into their grapes can shine through. Conversely, conventionally farmed juice often requires inoculation to replace yeasts damaged by vineyard pesticides and employ designer yeasts to alter their inherent flavor.
Next month, we savor fall in the vineyard.