Xylem
Cells within the grape vine that transport water and nutrients from the roots to the leaves.
Yeast
Single-celled micro-organisms that are key to fermentation. Yeasts are present naturally on grapes or can be added by the winemaker. As yeast grows is feeds on sugars in the grape juice and converts them into alcohol.
Yield
The harvest of grapes or production of wine per unit area of vineyard. In Europe yield is usually measured as hectolitres of wine per hectare, while in the New World yield is usually measured as tonnes of grapes per hectare, or tons per acre in the USA.
Young
Wine that has not gone through a length aging process.
Zinfandel
Grape variety most commonly associated with California, though it originated in Europe.
Zymology
The science of fermentation.
