Which compound is primarily produced by yeast during fermentation?

The primary compound produced by yeast during fermentation is ethanol. Yeast, particularly Saccharomyces cerevisiae, metabolizes sugars in the absence of oxygen through a process known as alcoholic fermentation. During this biochemical process, glucose is broken down, resulting in the formation of ethanol and carbon dioxide. While carbon dioxide is indeed produced and is crucial for the carbonation of beverages, the primary goal of the fermentation process, particularly in brewing and winemaking, is the production of ethanol, which is the alcohol found in these beverages.

The other compounds listed, such as lactic acid and acetic acid, are produced under different fermentation pathways. Lactic acid is primarily produced by lactic acid bacteria during lactic fermentation, commonly found in processes like yogurt production. Acetic acid is produced by acetic acid bacteria in the presence of oxygen, often during the oxidation of ethanol, which occurs in the production of vinegar rather than alcoholic beverages. Therefore, in the context of yeast fermentation specifically, ethanol stands out as the principal compound produced.