The Art of Wine Making: Choosing to Allow a Wine to Age On-Lees

Aging wine on lees (also known as sur lie aging) is a winemaking technique that can play a role in shaping the flavor, texture, and complexity of a wine—especially whites like Chardonnay, Champagne, and Muscadet, but also increasingly in reds and even natural wines.

Lees are the dead yeast cells and other solids (like grape skin particles) that remain in the wine after fermentation. There are two types (1) Gross lees which are heavy, coarse sediment that settles quickly and is usually removed and (2) the fine lees which are the smaller, finer particles that remain suspended longer and are typically the focus of lees aging.

After fermentation, the wine is left in contact with the fine lees for an extended period (ranging from a few months to several years). The winemaker may choose to stir the lees periodically (known as bâtonnage) to encourage more contact or leave the lees undisturbed to preserve freshness and minerality. Over time, the yeast cells break down and release compounds into the wine. 

Aging a wine on-lees can affect several aspects of the final product. It can add texture, giving the wine a richer, creamier mouthfeel. It also adds complexity to the wine with flavors of yeast, brioche, toast and even a bit of nuttiness. Finally, aging on-lees can naturally protect the wine against oxidation.

So, aging a wine on-lees is yet another part of the art of wine making. Cheers!

What are Lees in Winemaking?

A wine barrel with a clear end-cap shows the settled Fine Lees

I was recently hosting a wine tasting that involved a white wine. On the back label, it stated that the wine had been “Aged on lees.”  I was asked the obvious question “What are lees?”

In the broadest sense, “lees” refers to all the stuff that settles on the bottom of a wine fermentation or aging vessel (e.g., the tank or barrel). This “stuff” can include grape skin fragments, grape seeds, grape stems, pieces if grape leaves and, after fermentation, dead yeast. 

This collection of “stuff” is generally referred to as the “Gross Lees.” Not exactly because it might be considered ‘gross’ in its consistency, but because it is not the collection of stuff that you want your wine to be aged on. These items can to lead to some rather offense odors and flavors in a wine.

Wine makers generally “rack off” their wine (transfer it) to a fresh vessel or barrel that leaves behind the really chunky stuff and only moves the fermented wine, along with a bunch of dead yeast cells that don’t readily settle and remain mixed in with the newly fermented wine.  With aging, the dead yeast cells do settle to the bottom of the tank or barrel (see image).

When a wine is “Aged on Lees,” this contact with the dead yeast cell is allowed to continue throughout the aging process or until the wine maker determines they’ve achieved the desired wine characteristic. Wine makers even encourage the wine’s contact with the dead yeast cells, or “Fine Lees” by stirring the wine to move the lees off the bottom so that it can have more contact with the wine. The French term for this stirring technique is “Bâttonage.”

As the dead yeast cells break down during aging, they can bring out flavors of nuts, honey, bread, etc. They can also bind with tannins in the wine and to help smooth out the wine. So then, when the wine maker is happy with their wine’s characteristics, they let the Fine Lees settle and again carefully transfer (rack off) the wine and leave behind the layer of dead yeast cells that lay on the bottom of the aging vessel.