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!