Living substance responsible for the production of the enzymes that permit fermentation, the conversion of sugar into alcohol, with heat and carbon dioxide as by products. Yeast occurs naturally on grape skins, but many winemakers today use specially selected cultured yeasts to allow better control of the fermentation.
The distinctive smell of yeast (as in unbaked bread dough). In wine this usually indicates a fault, though the smell of freshly-baked bread can be desirable in Champagne and lees aged whites.
Quantity of grapes harvested from a given area of vineyard. Received wisdom is that low yield equals high quality, though in practice there are many factors at work, including density of plantation, local climate, etc. Yields are normally expressed in weight per unit area (tons per acre) or volume per unit area (hectolitres per hectare).