 However, even in the presence of abundant oxygen, some strains of yeast such as "Saccharomyces cerevisiae" prefer fermentation to aerobic respiration as long as there is an adequate supply of sugars (a phenomenon known as the Crabtree effect).Some fermentation processes involve obligate anaerobes, which cannot tolerate oxygen.Although yeast carries out the fermentation in the production of ethanol in beers, wines, and other alcoholic drinks, this is not the only possible agent