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104 WINES&VINES November 2015 WINEMAKING phenolic ripeness. During the vinification pro- cess, maceration is the fundamental stage for the properties of the wine. It lays the founda- tions for the quantity and quality of the com- plex development processes that characterize the aging of both great red wines and those meant to be consumed young. Factors of extraction The importance of this problem on a winemak- ing level has prompted ample scientific litera- ture in the past 50 years, with increasingly more detailed contributions, and it does not appear to have exhausted itself yet. Since Ribereau-Gayon's classic work in the 1960s and 70s, we have known how polyphe- nol extraction occurs with different dynamics between anthocyanins and tannins. The former reach a maximum in the initial stage of mac- eration-fermentation and then tend to decrease; the tannins, on the other hand, increase with skin and seed contact time. Various authors have shown that, on average, the fraction of polyphenols extracted is lower than 50% of the grape content, depending on the type of culti- var, the state of ripening and health reached by the grapes and the variables that control the process. The degree of grape skin ripeness influences the maceration process mainly at the initial stage (i.e., the degradation reached by the cell walls regulates the release of easily extractable phenolic substances). Higher levels of seed ripeness, linked to oxidation processes, make it more difficult to extract flavanols. The extraction process is undoubtedly in- fluenced by the solubility of phenolic com- pounds: It is higher in aqueous solution for anthocyanins than flavanols, especially poly- mers, but in both cases it increases with the alcohol content that increases during fermenta- tion. This, however, is not a limiting factor in itself. During maceration between different phases, the diffusive processes are clearly linked to the separation surfaces between phases. The release from the solid phase to the liquid one is controlled by the state of degrada- tion of the cell walls and membranes (poros- ity), as well as the diffusion process in the liquid phase and also the establishing of chemi- cal balances that involve the phenolic substances. The phenomena described are widely influ- enced by the chemical and physical conditions of the system, by the type of equipment used and by the operations applied. Among the chemical and physical variables are tempera- ture and duration of maceration, alcohol by volume and the use of sulfites. The different factors work in synergy among themselves, and it is not always easy to extrapolate the effect of one single parameter. The temperature at which maceration oc- curs in consequence of the fermentation phe- nomenon is considered a strategic factor of the extraction process, since higher temperatures correspond to a clear increase in polyphenolic CLASSIFICATION OF POLYPHENOLIC SUBSTANCES IN RED WINES Class Location in the grape C wine/gL -1 Spectrophotometric indices FLAVONOIDS TP TF Anthocyanins Monomers SK, P 0.1-0.6 TA Combined (polymeric pigments) Flavan-3-ols (Flavanols) Monomers (catechins) SE 0.15-0.2 FRV Proanthocyanidins (Condensed tannins) Oligomers SK, SE 1-5 PC Polymers SK, SE Flavonols SK 0.0015 NON FLAVONOIDS Phenolic acids Benzoic acids SK 0.05-0.1 Cinnamic acids SK, P 0.05-0.2 Hydroxystilbenes SK <0.0005 Abbreviations: SK (skin), SE (seeds), P (pulp), TP (total polyphenols), TF (total flavonoids), TA (total anthocyanins), FRV (flavanols reactive to vanillin and to dimethylcinnamaldehyde), PC (proanthocyanidins). The location of tannins is noted in the berry structure above. Skin tannins depicted above are shown both free and attached to components of the cell structures. Source: Saint-Criq et al., 1998 Free tannins Vacuolar membrane Tannins attached to the membrane Cell wall Tannins attached to the wall Locule Pulp Skin Peripheral vascular tissue Vascular tissue Seed Coat Endosperm Embryo