In 2005, a portion of our Paolo's Vineyard Syrah was fermented naturally, without adding any yeast—which had a profound affect on the wine. Instead of intentionally adding a single cultured yeast, Lise allowed the yeasts from vineyard, winery, and/or winery equipment to convert the sugar to alcohol. In fact several species of yeast probably performed the fermentation. Natural fermentations (aka native fermentations, spontaneous fermentations) have been making a comeback because they tend to lead to more complex flavors, a smoother texture and a more site-specific character in the wine.
The advantages of a natural fermentation, however, do not come without risks. Most strains of yeast are not optimal for making wine because they can produce off aromas and flavors. In addition, many natural fermentations become "stuck", where the yeasts die off before they've fermented the wine to dryness (leading to a sweet wine)—typically because the yeasts can't tolerate high alcohol and temperature. Luckily, we didn't have either of these problems in 2005.
Our goal with this fermentation experiment was to produce a more complex wine, one with smoother texture and breadth of flavor. In her winemaking, Lise focuses on mouthfeel because she believes this to be the most important impact a winemaker can make. Aromas and tannins, for example, are best left to the grapes themselves. A winemaker can affect texture through fermentation style, extended maceration, and fining (such as with egg whites). In the case of our 2005 natural fermentation experiment, we were definitely pleased with the silky texture of the wine. Let us know what you think!