Enzymes in winemaking

Abstract

It is generally accepted that grape composition plays a primary role in determining the final quality of wine. However, many of the sensory characteristics that are normally used to assess the quality of a wine, including those that are considered typical of the grape variety, cannot be detected in the grapes. They develop in fact, in large part, through a complex array of biochemical reactions that take place during the winemaking process. The majority of these reactions are catalyzed by different enzymes coming form various sources, particularly grapes and microorganisms. Many sensorially-active constituents of wine are affected, at different stages of winemaking, by biochemical transformations that are catalyzed by specific enzymes. For example, enzymes are involved in the oxidation of grape phenolics, in the formation of volatile compounds during pre-fermentative operations, and in the transformation of odorless precursors into odor-active compounds during alcoholic and malolactic fermentations. Also, the extent of certain enzymatic reactions can determine the efficiency of specific technological steps considered to be of primary importance in the modern wine industry, such as juice and wine clarification, color extraction, and protein stabilization. Therefore, understanding the role played by enzymes during winemaking can help in the development of rational and effective strategies for optimizingwine processing to modulatewine composition and sensory properties. Grape berries and wine yeasts are the major sources of enzymes involved in the various biochemical transformations that take place during winemaking. However, typical winemaking conditions such as high sugars and ethanol concentrations, low pH and high concentrations of polyphenols, can potentially inhibit the activity of grape and microbial enzymes, often with synergistic interactions which result in enhanced inhibitory effects. For this reason, the reactions catalyzed by grape and microbial enzymes during winemaking are often incomplete, with a significant portion of the substrate remaining untransformed and therefore available for further reaction. Because many of these reactions are considered beneficial to wine quality or to the efficiency of specific technological operations, the addition of exogenous enzymes that exhibit higher efficacy under winemaking conditions is frequently carried out in the winery to obtain the desired level of substrate transformation. Exogenous enzymes are an important component of modern winemaking, and many industrial preparations are now commercially available, particularly to assist during juice and wine clarification and to increase liberation of aroma compounds from odorless precursors. This chapter provides an updated overview of the current knowledge on the role played by enzymes in the process of transforming grapes into wine and on the possibility offered by new technologies to modify wine composition though a more effective control of enzymatic reactions. © Springer Science+Business Media, LLC 2009.