Yeast: Micro-organisms that convert sugar to alcohol and carbon dioxide in the process known as fermentation; they can be natural or commercial.
Yield: The amount of grapes harvested in a particular year; also, measures the productivity of a vineyard.
Young: And immature wine that is usually bottled and sold within a year of its vintage.
Zero Dosage: See Brut Nature.
Zinfandel: A popular grape in California of disputed origin; scientists say it is related to grapes in Croatia and southern Italy.