We all know that without yeast, there’s no wine. But aside from winemakers and sommeliers, few people realize that fermentation is a complex process, one that is neither foolproof nor straightforward. True, if left to their own devices as they ripen, grape skins will crack and their juice will ferment. But the microbiome in each and every grape must (vintners refer to the mixture composed of pressed juice as well as skins, seeds, and stems as “must”) is an intricate ecosystem, one informed and complicated by the range of specific yeast strains living in and around the vineyard as well as the strains floating through the air in the wine cellar where the must ferments. During what vintners call “spontaneous” or “ambient” fermentation, the various yeast strains present in the must begin carrying out fermentation as a group. Eventually, if all goes right, the strain called Saccharomyces cerevisiae begins to dominate.
At Pisoni’s winery, Jeff, the family’s vintner, places a drop of grape juice beginning the journey that will transform into Pinot Noir on a microscope slide. If you’re fortunate to be there alongside him, you can take your turn before the eyepiece of the microscope that resides at the family’s winery and find yourself a witness to a strange and beautiful world. Magnified four hundred times by the lens, strains of native yeast float and bud and divide. During the first several days of spontaneous fermentation, a few small dark ovals swim in what appears to be almost solitary splendor under the microscope lens. But if you return to the winery and observe Jeff repeat the practice one or two days later, you’ll find the small globe of juice teeming with activity. Illuminated by the microscope’s light, countless circular cells of Saccharomyces cerevisiae hover below the eyepiece. They are rimmed as if haloed by the microscope’s light. Wait a moment, and watch a second circle begin to emerge from the first. This splitting of the particular strain of yeast cells that drives fermentation up to 13 or 14% alcohol is exactly what Jeff has been waiting for.
Unsurprisingly, most winemakers don’t wait for nature to begin this process on her own. Instead, they produce wine by inoculating the juice of their grapes with strains of what are called “cultured” yeasts. (If you bake bread at home, you are already familiar with what is essentially the same general process when you purchase cultured yeast to initiate bread fermentation.) The yeast strains propagated in labs that vintners purchase are known strains with consistent character and fermentation rates. For some wineries such consistency is often highly valued.
Pisoni does things differently. An artisanal winery, Pisoni can afford to make wine that is true to ideals. Jeff explains that the family has long been committed to what is called by turns “natural,” “ambient,” and “spontaneous” yeast fermentation.
We fill the tanks and wait patiently. I love the wine quality and philosophy of native fermentation.
“My brother Mark and I view grape-growing and winemaking as expressions of place. I don’t want to manipulate fermentation because that feels to me like forcing our wine into a mold,” Jeff continues while climbing a ladder up the outside of a fermentation tank in which three tons of pinot noir will stay for its first two weeks. He eyes the thickness of the cap, that layer of grape skins pushed to the top of the tank by rising carbon dioxide during fermentation, the initial period when the wine remains in contact with seeds, skins, and stems.
“Some people say that the yeast gives certain flavors to the wine. Our grapes are in the tank for about a week before they start to ferment. If you inoculate, you prompt fermentation the next day. If you choose not to inoculate, the slowness of the process at the start, the interaction between different strains of yeast before dominant strains of Saccharomyces take over, the longer maceration time of the skins, which allows for more color and flavor”–here he punches through the cap with his arm to demonstrate its thickness as well as to feel for the heat simmering below the surface where the yeast is doing its work of fermentation–“these things all contribute complexity.”
Using native yeasts does not mean that the Pisonis blindly close their eyes and hope, however. Certainly, spontaneous fermentation with native yeast is riskier: “You have only one shot to establish your population,” Jeff notes. “When you fill a three or five-ton tank with grapes, it’s as nerve-wracking a time as it is exciting. The juice sits there, a few days pass, you watch and wait and walk by and look and taste. So much is dependent upon the yeasts.” But Jeff and his colleagues at Pisoni’s winery do not simply wait. Look around the winery and find not only the microscope but also the enzymatic analyzer and other equipment to measure and monitor the fermentations. During the first few days before fermentation gets going, as well as throughout the process, Jeff supervises the daily collection of data on the wine’s transformation. “Most wineries that produce under 10,000 cases do not perform very much analysis. But I like information for what it can tell us– and for its own sake. Just as Mark collects a lot of information on weather and soil in the vineyard, we gather data we feel can help us understand fermentation better.” He gestures toward a series of small cups of wine samples which he and Caroline Davis, the Pisoni enologist, will later evaluate. “We pull multiple samples from each tank every day: for both tasting and analysis.”
“I wouldn’t take this approach with every vineyard. Working with native yeasts is unpredictable.” He smiles. “But we really do know these grapes through and through. With Mark in the vineyard, I have strong confidence in the fruit. The goal is to make wine using a hands-off, non-intervention style. By using native yeast, I think we start that process off very well.”