What is the simplified definition of fermentation?

The correct definition of fermentation is the conversion of sugar into alcohol and carbon dioxide gas by yeasts. This is a fundamental biological process that occurs during the production of alcoholic beverages, including wine. Yeasts consume the sugars present in grapes or other fruit and ferment them, producing alcohol as a byproduct. This process not only produces alcohol but also contributes to the development of unique flavors and aromas in the wine. It is essential to the winemaking process, as without fermentation, there would be no alcohol content in the finished product.

The other options relate to different aspects of winemaking but do not define fermentation itself. Blending wines enhances flavor but does not involve the conversion of sugar. Filtering is a clarification process used after fermentation to remove solids from the wine. Aging refers to the maturation of wine in barrels or bottles, which can enhance complexity but occurs after fermentation has completed.