What is a key function of yeast in fermentation?

The key function of yeast in fermentation is to transform sugar into alcohol. During the fermentation process, yeast consumes the sugars present in the must or mash and converts them into ethanol (alcohol) and carbon dioxide through the process of anaerobic respiration. This transformation is crucial in the production of alcoholic beverages, including sake, as it directly affects the alcohol content and creates the characteristic flavors and aromas associated with the beverage.

While yeast does produce carbon dioxide as a byproduct of fermentation, its primary role is not limited to this aspect. The prevention of spoilage is also important in the fermentation process, but it is primarily the alcohol produced that helps inhibit the growth of undesirable microorganisms, rather than being a direct function of yeast. Additionally, while yeast can play a role in enhancing the taste profile, its main function during fermentation remains the conversion of sugar into alcohol.