Definition - What does Yeasty mean?
Yeasty is an aroma descriptor identified in wines which have been aged via sur lie. This type of aging is often only reserved for white wines and/or sparkling wine and Champagne. The wines are aged in holding vats or vessels in which the yeast cells are present. This allows the aroma characteristics of the yeast to be imparted into the wine.
WineFrog explains Yeasty
If a wine is described as "yeasty," it indicates that the wine was aged sur lie, or "on the bed of the lees." Lees are the yeast cells which settle to the bottom of a wine vat or vessel. This type of aging is commonly reserved for sparkling and Champagne wines or white wines. By aging on the lees, they impart yeasty characteristics into the wine. They also add structure and texture to a wine which is often described as "creamy" or "silky." The aromas of the yeast are found in the bouquet of the wine which resemble yeast-like smells, i.e., raw bread dough, baker's yeast, fresh baked bread, etc.