Micro-organisms that convert sugar to alcohol and carbon dioxide in the process known as fermentation. The predominant wine yeast, saccharomyces cerevisiae, is the same micro-organism that ferments beer and makes bread dough rise.
The quantity of grapes or wine produced measured in tons per acre or hectoliters per hectare. Although it is true that overcropped vines with high yields produce less-concentrated grapes, it is not true that lower yields always mean higher quality. Different soils, vineyards and varieties are able to successfully carry different levels of crop.