Microbial enzymes: Relevance for winemaking

Production of wine from grape juice is predominantly the result of complex enzymatic reactions. The primary bioconversion of grape sugar to ethanol and CO by the yeast Saccharomyces cerevisiae is catalyzed by cytosolic enzymes. In spontaneous must fermentations, also strains of Saccharomyces bayanus or interspecies hybrids may dominate, probably because of better adaptation to specific environmental conditions. In addition, various enzymes released into the must influence the final composition, color, and sensory properties of wines. These enzymes originate from the grape itself, from epiphytic fungi like Botrytis cinerea, and from yeasts and bacteria associated with vineyards and wine cellars. Especially non-Saccharomyces yeasts, also called "wild” yeasts, belonging to the genera Kloeckera, Candida, Debaryomyces, Rhodotorula, Pichia, Wickerhamomyces, Zygosaccharomyces, Hanseniaspora, Kluyveromyces, and Metschnikowia, secrete different hydrolytic enzymes (esterases, lipases, glycosidases, glucanases, pectinases, amylases, proteases) which interact with grape compounds. Apart from yeasts, enzymes of lactic acid bacteria have a significant impact on wine quality.