Zymase's an enzyme complex ("mixture") that catalyzes the fermentation of sugar into ethanol and carbon dioxide. As the conversion takes place, the reaction will gradually slow down. They occur naturally in yeasts. See alcohol dehydrogenase. Zymase was first isolated from the yeast cell in 1897 by a German chemist named Eduard Buchner who fermented sugar in the laboratory without living cells, leading to 1907 Nobel Prize in Chemistry. Cell-free fermentation experiment The experiment for which Bu… (More on Zymase)