The biological process of winemaking is the result of a series of biochemical transformations caused by the action of several enzymes. Many of these enzymes originate from the grapes themselve. In addition, since the endogenous enzymes of grapes, yeasts and other microorganisms are often neither efficient nor sufficient under winemaking conditions, commercial enzyme preparations are also widely used as supplements. Several of commercial enzyme preparations are very commonly used in winemaking (pectinases), while others are not so widely used (urease). The typical winemaking process and enzymes are illustrated in Figure 1.

Figure 1. Typical production process of red wines showing the stages at which enzymes are added.(Ray, et al. 2017)

Use Enzymes to Improve Maceration

Color is one of the most important attributes in the preliminary assessment of red wine. High-colored wines are usually associated with high perceived quality scores. Anthocyanins contribute greatly to the sensory quality of red wines because these molecules and their interactions with other phenolic compounds are responsible for the color and the stability of red wine during ageing. Exogenous enzymes are widely used in red winemaking, trying to accelerate the extraction of anthocyanins from the berry skin and thus increasing the color intensity of the resulting wine. Commercial enzyme preparations are mainly characterized by the activities of pectolytic (polygalacturonase, pectin methyl esterase and pectin lyase) cellulase, hemicellulase, and acid protease.

Use Enzymes to Improve Clarification, Filtration and Yield

The addition of commercial enzymes (i.e. pectinases, xylanases, glucanases, proteases) to improve clarification and filtration and to increase the pressing efficiency and juice extraction is a common practice in winemaking. Pectinases are the most important enzymes in winemaking. Together with cellulose, hemicellulose, and lignin, pectic compounds form part of the grape cell wall and act as adherents between cells giving consistency to the cell wall. The rupture of these cell structures favors the extraction of substances contained within the solid part of the grape, mainly in the pulp and in the skin. Pectolytic enzymes break down these compounds and improve the extraction and clarification processes of the must. They can also favor the extraction of substances that affect the aroma and color contained in the skin and in the pulp.

Assisted Wine Aging on Lees with β-Glucanase

In wines, once the alcoholic fermentation has finished, an aging on lees takes place for a variable period according to their particular features. Lees are mainly composed by microorganisms (yeasts and bacteria) and to a lesser extent by tartaric acid and inorganic matter. During aging on lees, the autolysis of wine yeasts occurs, modifying the chemical and sensorial characteristics of the wine. Yeast autolysis involves the hydrolysis of biopolymers under the action of hydrolytic enzymes (β-glucanases and proteases among them) which release different compounds into the wine. Peptides, amino acids, fatty acids and nucleotides come from the yeast cytoplasm, while glucans and manno-proteins come from the yeast cell wall. These compounds have a capital implication in the organoleptic properties and stability of the wines, and in the foaming of sparkling wines. The period of aging on lees is variable according to the particular desired wine features, although a longer time positively contribute to the quality of the wine. In order to reduce this long period, and therefore the risks of oxidation and microbial contamination and the high costs of production, enzymatic preparations rich in b-glucanases can be utilized. Exogenous glucanases can catalyze the hydrolysis of b-(1-3) and b-(1-6)-glycosidic bonds of the cell wall b-glucan chains, progressively degrading the cell wall and accelerating the yeast lysis.

Use Enzymes to Enhance Wine Aroma

Varietal aroma of grapes includes volatile free odor substances (mainly monoterpenes, C13-norisoprenoids, benzene derivatives and long-chain aliphatic alcohols) and odorless non-volatile glycoconjugates. Glycosidically bound volatiles are composed by glucose and also by rhamnose, arabinose or apiose in disaccharides glycosides. These glycosidic aroma precursors can give rise to odorous volatiles using exogenous glycosidases. Usually, this process involves a two-step mode reaction. Firstly, a-rhamnosidase, a-arabinosidase or b-apiosidase release the terminal sugar (according to the sugar moieties of the substrates); secondly, a b-glucosidase liberates the aromatic aglycone and glucose.

It has been demonstrated that the glycosidic aroma precursors remain stable during winemaking operations since the effect of grape and S. cerevisiae glycosidases is very limited. For that, the selection of active yeast, fungal and bacterial glycosidases to enhance the wine aroma has been extensively studied. At present, commercial preparations, rich in glycosidases, are available from Aspergillus niger. These fungal enzymes are active under winemaking conditions; however, because of their inhibition by glucose, they must be added at the end of fermentation.

Reference

1. Ray, Ramesh C., and Cristina M. Rosell, eds. Microbial enzyme technology in food applications. CRC Press, 2017.

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