What does "on the lees" mean in wine production?

The term "on the lees" refers to the practice of leaving wine in contact with dead yeast cells after fermentation. This process can enhance the wine’s texture, complexity, and flavor profile, imparting a richer mouthfeel and adding layers of aromas and tastes that might not develop otherwise. The dead yeast cells, known as "lees," contribute to the development of compound flavors through autolysis, where the yeast breaks down and releases various compounds into the wine.

Leaving a wine on the lees is commonly practiced in the production of certain styles of white wines, such as Chardonnay, and is essential in sparkling wine production, particularly in styles like Champagne where it contributes significantly to the wine's character. The practice is a critical aspect of winemaking that helps to create a more nuanced and sophisticated final product.