Get to Know Lees, the ‘Magical Fixer’ That Transforms Wine into Rich, Textural Gems

BY KATE DINGWALL. THE WINE ENTHUSIAST

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Talking about lees can be a bit of inside baseball. There’s lingo and know-how required to debunk whether a wine is lees-y, or how extended lees aging has affected what you’re sipping. 

That’s largely because lees—something part science project, part sorcery—are a tricky topic to fully grasp. One thing is clear, though: They can turn even a standard wine into a textural gem, adding structure, breadth and bready characteristics.

Confused? Don’t be. We asked winemakers to run us through Lees 101 and unpack the pluses and minuses of lees aging.

What Are Lees?

Simply put, lees are dead yeast cells left over from the fermentation process. 

Once grapes are pressed, yeast is added to the juice to kick-start fermentation. Those yeast cells help convert sugar into alcohol and carbon dioxide. Once they’ve done their job and the yeast has consumed all the sugar, the spent yeast cells die off and drop to the bottom of the fermentation vessel, along with the material from the grapes’ skins and other solid remnants of the fermentation process. 

That wet, dense pile of residual mass is called the gross lees. It’s a mix of dead yeast, grape skins, seeds, stems and tartrates produced in the first few hours of fermentation. 

Another type of lees, known as fine lees, are mostly made of dead yeast cells that gradually settle on the bottom of a fermentation vessel. They have a silkier consistency than gross lees, and are both a byproduct of winemaking and an ingredient in its aging process. 

While gross lees—which can be relatively volatile—are often racked off and discarded, fine lees are a winemaker’s darling. Inside the dead yeast cells are a plethora of important compounds, proteins and molecules, like mannoproteins, polysaccharides, fatty acids and amino acids.

Mannoproteins are protein groups that add mouthfeel, aroma, flavor and soften tannins. Polysaccharides—bonded groups of sugar molecules—can reduce the astringency of tannins and create balance and structure in the body of the wine. Fatty acids, which are contained within the cell walls of the yeast, help boost various flavors and aromas. Amino acids have a similar impact, and can also improve texture.

Why Do Winemakers Use Lees?

Many winemakers, including specialists in white Burgundy and traditional method sparkling wines, swear by a wine’s time spent on lees. So does Tara Gomez, winemaker for Camins 2 Dreams in Lompoc, California, who ages a Southern Rhône blend of Marsanne, Roussanne and Grenache Blanc on the lees. It adds “texture, depth, complexity and flavor to the wine,” she says.

But working with lees can also be a little unpredictable. 

“Lees are like the drunk uncle at a family gathering,” says cicerone Toni Boyce. “It gives a beverage life, but if it overstays its welcome, things could turn left quickly.”

Lees aging—also known as sur lie, French for “on lees”—is the process of wines mature and age on top of spent yeast (and some other particulate matter). 

What Do Wines Aged on Their Lees Taste Like?

Aging on lees helps develop pronounced round, full, creamy flavors that may present as nutty or yeasty, or add notes of caramel, smoke, clove, warm brioche or buttered toast. In sparkling wines, like Champagne, extended lees contact can present as cheesy or as notes of buttermilk. 

Lees aging is common with Chablis, Muscadet and California Chardonnay. Some wines have less of those warm, savory flavors, while others wines explode with rich, bready notes due to bâtonnage (more on that later). This style of winemaking is also used with oak-aged California Chardonnay to achieve its iconic warm, buttery and creamy qualities.

Here’s how it works: During the early stages, usually the first few months, the main benefit of lees aging is to prevent unwanted oxidation. Mannoproteins will absorb residual oxygen that could cause undesired oxidation, and dull both the color and flavor.

The presence of mannoproteins is also the key to malolactic fermentation, a process crucial for nearly all red wines and some whites. The malolactic bacteria eat the mannoproteins, aiding the process.

The longer wine ages on its lees, the more body and dimensions it develops. Champagne is aged at least 12 months on lees for non-vintage bottles, and a minimum of 36 months for vintage cuvées. 

While most lees-aged wines sit in vessels (oak, eggs or foudres), Champagne rests in individual bottles that are rotated during the aging process, and then slowly angled so the lees collect in the neck to be removed at the end of the aging period—a process known as riddling.

To Stir or Not to Stir?

Some winemakers will stir lees—bâtonnage—during the post-fermentation process. Bâtonnage calls for a winemaker to disrupt the expired yeast cells by stirring, or gentle agitation. It helps extract flavor and aromas, and adds texture to a wine, like swirling sugar in your coffee. 

By stirring the lees instead of simply letting them sit at the bottom of the barrel for the entire aging period, winemakers can create more uniform interactions with the wine in the barrel. It breaks down the yeast cell walls more quickly to release compounds into the wine.

“It’s like cream in coffee or a lava lamp,” says Cara Morrison, Chardonnay winemaker at California’s Sonoma-Cutrer.

What Else Do Lees Add to Wine?

Beyond the basic fermentation, winemakers can get weird with the dead yeast cells. At Oregon’s Appassionata Estates, Riesling from old vines sits for twelve months on lees before it’s bottled. 

Maya Hood White, the winemaker and viticulturist at Virginia’s Early Mountain Vineyards (and one of Wine Enthusiast’s 2024 Winemaker of the Year nominees) uses a “perpetual lees” aging technique, where she blesses new vintages with a continuous, solera-style set of lees to add depth and complexity. 

Her Intention—a nod to white Bordeaux—stays on two years to gain more of autolytic (brioche-like and bready) characteristics. “It’s almost like a long-aged, sur lie sparkling wine, but without the bubbles,” says Hood White.

Elsewhere, she matches Petit Manseng with a longer lees exposure to help naturally manipulate the grape. “[Working with lees] is giving us an extra tool to make the kind of wines we want to produce,” says Hood White. 

“Petit Manseng can have such ripping acidity. Lees aging mitigates that acidity.” The lees characteristics also show off the grape’s aromatics in a different, more pronounced way. “Petit manseng has such exceptional aromatics to it,” Hood White continues.

Tim Malone, an avid lees nerd and winemaker of Appassionata Estates, loves lees because they add structure while retaining a brightness—something that can at times elude wines aged in oak. 

Even after a year or two on lees, “there’s freshness and liveliness to the wine that will hopefully last well into the aging process,” says Malone. He nods to Ernst Loosen’s Riesling, which spends up to ten years on the lees in large-format casks. “It’s the lees that keep them fresh!”

Molecular Alchemy

Hood White and Malone also love working with lees because of the intangibles. 

Hood White—who uses ambient yeast cultivated around the winery—finds lees “a more dynamic representation of place because there’s a different microbiological life to them.” Lees are like little minions, each one doing a small bit of work that adds up over time. But don’t expect them to always behave exactly like you think they should.

“They’re wildly temperamental to the weather,” says Hood-White. “When we get a cold snap in January, our fermentations slow down. Come April or May, all of these fermentations start to take off again—they truly have a life of their own.”

Malone employs lees as a corrective tool. “They’re a magical fixer,” he says. If neighboring vineyards have overspray sulfur, lees contact can help correct the impact. “You can get too much reduction and it will smell awful,” says Malone. “We could use copper, [but that] will screw up your palate and knock a great wine down a peg. Once we press the wine and get it off skins, we’ve found that multiple applications of lees will absorb a lot of those advanced sulfur compounds, basically cleaning up that wine.”

“Dead yeast cells—even prior to death—are scavengers of oxygen and toxins,” Malone continues. That said, it can be a tricky dance—lees absorb things that keep primary fermentation going. “But we also use lees and yeast cells to revive a stuck fermentation.”

Can I See Lees in Wine?

Oftentimes, lees can end up lingering in the bottom of your glass. None of this is cause for concern—those white crystals or red sludge (tartrate crystals) in your glass are a sign of a wine made with minimal intervention or without filtration. 

Those crystals are bits of potassium bitartrate or calcium bitartrate. Remember chemistry class? Heat helps solid substances dissolve, while cooling the temperature back down will turn those solids back into crystal form. 

They aren’t harmful to drink, but if you’re averse to the texture, sediment can be removed easily with a fine-mesh sieve, a layer or two of cheesecloth or a thin coffee filter to avoid leaving those crystalline gunks in your mouth after every sip.