Alcohol has been celebrated with awe for millennia. This mysterious transfiguration of sugar has inspired lore and legend, even religion, until the 19th century when Louis Pasteur proved that yeast is the mechanism at play. We now understand, in winemaking, a variety of yeast strains carry out the primary conversion of grape sugar into alcohol. Only a few wines, however, utilize the yeast post-fermentation to add novel aromas, flavors, and textures that become a hallmark of the wine.
When yeast have completed their primary task and fermentable sugars have turned to alcohol, the energetic yeast begin to rest and settle to the bottom of the fermentation vessel. Many styles of wine require winemakers to then rack, or move, the wine into another vessel and away from a majority of the yeast.
This spent yeast, now called lees, has the power to rob wines of their fruitiness, freshness, and energy. Move the wine off the lees or lose the wine’s spark. That is unless you’re making fine sparkling wine or a great chardonnay—these can attribute a part of their greatness to time spent with the dead yeast.
As the lees transition from dormancy to death, the yeast give themselves up to the wine. “As the yeast cell wall begins to breakdown, a couple of months after fermentation finishes, the contents of the cell wall are released into the wine” explains Eric Hamacher of Hamacher Wines in Oregon’s Willamette Valley.
This breakdown is an auto-digestion of the cell wall called autolysis. Early stages of autolysis produce gentle suggestions of bread dough. With more time, the impact becomes more profound. Sean Thompson, director of winemaking at Schramsberg Vineyards in Napa Valley elaborates, “After eight years, we start to see marzipan, chicken stock, crème brûlée, and flavors of fruits baked in a pie or crumble. The autolytic characteristics bloom slowly over time.”
Beyond the flavor profile, Thompson adds, “Autolysis increases the mouthfeel of the wine and builds additional layers of sweet aldehydes and baked elements in both the flavor and aroma of the wine.” This combination of aromatic complexity and textural weight brings winemakers to worship at the altar of autolysis.
Schramsberg Vineyards is a sparkling wine house, a style of wine where time on the lees gets compounded. While a chardonnay might spend 10–18 months on the lees, traditional sparkling producers will keep the lees in their bottles for two-to-five years commonly, and occasionally up to 10–20 years.
“As a wine is left on the yeast and exposed to the autolysis for a longer period of time, the fresher fruit elements of the wine will slowly caramelize,” says Thompson. “This process is faster in still wines due to the presence of oxygen, but in a sparkling wine the CO2 provides an insulating blanket for the wine, providing a barrier for any oxygen egress that could be present.”
CO2 combines with much higher levels of acidity in sparkling wine to slow the autolytic process, requiring this extra time on the lees to impact the wine. Schramsberg Vineyards’ 2010 J. Schram spent nearly eight years on the lees and showcases a beautiful balance of sweetened baked goods and still persistent lemon transitioning to lemon bar.
At Equinox Wine in California’s Santa Cruz Mountains, another sparkling house, the 2001 Equinox Chardonnay Blanc de Blanc Extended Tirage spent a whopping 17 years on the lees, creating an oxidized, hyper-carmelized and rich profile layered with golden raisin and buckwheat honey. This perceived sweetness gained over time is alluring.
“A chief component of these autolytic compounds is glycerol,” Hamacher explains. “It has very high viscosity and is quite sweet. Unlike sugar, it is not fermentable so its sweetness is stable and does not interfere with other flavors the way sugar does. It gives the impression of sweetness without lingering.”
Autolytic flavors offer richness, texture, and unique aromatics. Ian Burch, winemaker at Archery Summit in the Dundee Hills of Oregon, appreciates the role of lees in his pantry of options. “Lees to a winemaker is like salt to a chef. I go heavy with the lees in my winemaking process from the get-go because once the lees are gone, or they are in very small quantities, it’s impossible to take advantage of their subtle but generous contributions.”