Winemaking anthocyanins

Port-type ted dessert wines require skin contact time to extract the anthocyanins, but the fermentation must be short to retain the sugar level neat the 6—10% level desired. The winemaker cannot always achieve desired composition in individual lots. In order to teach the desired standard, it is necessary to make new lots to enable blending to that standard. The right volume of a tedder, less sweet wine will need to be made to bring to standard a lot with low color and mote sugar, for example, while keeping the alcohol also within the desired limits. 

Even when no additive is used in winemaking, the necessity for small-lot trial before production scale operation is apparent. Because a high percentage of wine is consumed only after chilling, and because chilling may accelerate the precipitation of potassium acid tartrate, ill-defined colloids, anthocyanin-tannin polymers, proteins, etc., simple cold stabilization by refrigeration in the winery may irreversibly alter the product and its eventually-perceived quality level. It often happens, especially in heavy-bodied red varietal wines, that a dark, amorphous precipitate may form in the bottle over several years. Usually tannoid,... 

The fermentation usually is complete within 30 or 40 days. During this period additional anthocyanins are extracted from pomace and the color stabilizes due to polymerization between the anthocyanins and tannins. Winemakers call this process pomace "maturation". Moreover, due to the increasing alcohol concentration, many other metabolites are extracted from the pomace. In addition, yeast metabolites contribute to the aromatic complexity of the wine. 

A.2 Chemical Reactions of Anthocyanins During Winemaking Main Anthocyanin-... 

Fig. 9A.3 Main chemical reactions of anthocyanins during winemaking...

While the identity of the relevant yeast metabolites in the fermented medium sampled at day 2 needs to be clarified, previously published data have provided some evidence about the role of acetaldehyde-mediated condensation of catechin with MSG (13-20). We therefore aimed to extend these model studies and to confirm chemical formation of pigmented polymers from condensed tannins, which are commercially used in red winemaking, and anthocyanins. The model reactions were conducted with vatying concentrations of acetaldehyde and SO2 as shown in Table 2 and analysed by HPLC after 2, 4 and 7 days. After 7 days visible precipitation of unidentified material started to occur in presence of acetaldehyde and the reactions were discontinued. 

Along with changes in anthocyanin and tanin proportions, winemaking practices can bring additional components in wines through selection of fermentation yeasts. Enzymatic activities of particular yeast strain influence the release of volatile phenols, pyruvic acid and acetaldehyde and, therefore, control the relative proportions of the corresponding pyranoanthocyanins. 

The tact that grape solids as well as yeast lees adsorb anthocyanins is no secret to winemakers, as these materials are always darkened by pigment when removed from a fermentation. Yeast lees also have been shown to adsorb anthocyanins (1), and grape solids have been shown to re adsorb pigment (D. Block and D. Bone, personal communication). However, an estimate of the proportion of these losses as well as an estimate of the proportion of anthocyanin extracted has not previously been possible. 

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