4. Concluding remarks

eventually, precipitation. Singleton and Trousdale reported that white wines produced with added tannins and anthocyanins showed a linear increase in polymeric pigment content after addition of seed tannins in the range of 0 to 1000 mg/L (gallic acid equivalents) and anthocyanins in the range of 0 to 500 mg/L [53]. Using protein precipitation, Harbertson et al. found that large polymeric pigments (LPP), which precipitate BSA, increased by 70% between pressing and 185-day postpressing in Merlot wines [58]. Small polymeric pigments (SPP), which do not precipitate BSA, and are assumed to be composed of tannin-anthocyanin dimers, either of direct condensation or mediated by acetaldehyde [231], comparatively increased 30% from pressing to 185-day postpressing. In this same experiment, wines produced with extended maceration and saignée<sup>6</sup> and containing a higher concentration of tannins gave rise to an enhanced formation of LPP; however, this occurred with a decline in the anthocyanin content of 43% relative to its peak concentration [58]. A similar trend was observed in Merlot wines obtained with extended maceration (30 days), in which a two-fold increase of the total polymeric pigments was observed from day 4 to day 30, along with significant losses of malvidin, delphinidin, petunidin, and peonidin anthocyanin derivatives [47]. Furthermore, this later work demonstrated that the formation of polymeric pigments alone during extended maceration was only partially responsible for the observed anthocyanin loss because an increase in the polymeric pigment content of 13 mg/L from day 4 to day 30 occurred along with a drop in wine anthocyanins of 231 mg/L in this same time frame. In summary, these results suggest a complex relationship between tannin content, anthocyanin extraction (or loss), and polymeric pigment formation during maceration. As shown in Figure 15, a common feature of extended maceration seems to be the formation of polymeric pigments with the ability to precipitate BSA (and by a similar mechanism to elicit astringency), but this occurs at the expense of anthocyanin loss (and, consequently, of wine color saturation) (although this anthocyanin loss is generally not fully explained by the formation

The practice of saignée consists of taking a portion of the must from the bottom of the tank before the onset of alcoholic fermentation with the aim of increasing the solid to volume ratio of the remaining must and then furthering the extraction

Figure 15. Overview of the formation of polymeric pigments during maceration and bottle aging of Cabernet Sauvignon wines processed with a maceration length of 10 days (control) (a) and 30 days (extended maceration) (b). SPP: small

polymeric pigments; LPP: large polymeric pigments. Adapted from Ref. [43].

178 Phenolic Compounds - Natural Sources, Importance and Applications

6

of phenolics and aroma compounds from seeds and skins.

The above literature review was undertaken with the aim to highlight the remarkable chemical diversity of flavonoid phenolic compounds in grapes and wines. This diversity is furthered from the very first moment the grapes are crushed, thereby allowing vacuolar and pulp components to be released into the fermenting must and wine. This chemical diversity further increases during winemaking and bottle aging, thus adding to the already present chemical diversity, a variety of new sensory dimensions, ranging from changes in wine color and aroma to modification of astringency.

For a wide number of red grape varieties, the extraction of anthocyanins peaks during the first 4 or 5 days of maceration, which is followed by a decrease in concentration along with the lengthening of maceration. This decrease in anthocyanin concentration is typically accompanied by the formation of polymeric pigments, by which formation is modulated, among others, by the molar proportion of anthocyanins and tannins. Flavan-3-ols and small oligomeric tannins from skins are extracted within the first days of maceration, whereas the extraction of seed-derived tannins requires longer maceration times. It also seems that high molecular weight tannins are not retained into wine, probably due to interactions with polysaccharides and other nonphenolic materials during winemaking. Indeed, specific matrix effects affect the rate of retention of tannins into wine, particularly at the latter stages of maceration. These include (but are not limited to) the presence of anthocyanins, polysaccharides, and other cell-wall components such as structural proteins. As phenolic and nonphenolic compounds are extracted and/or formed during maceration and aging, a dynamic set of chemical and biochemical reactions occurs, resulting in the formation of new structures not previously found in grapes. Some of these new phenolic classes, which may also contain nonphenolic material of yeast and/or grape origin, are responsible for a variety of new sensory attributes. Polymeric pigments, bearing astringent and bitter properties different from those of intact tannins of equivalent molecular weight, are candidates for the changes in the mouthfeel and textural properties of red wines during maceration and aging. Although the taste and mouthfeel attributes of polymeric pigments are starting to be clarified, their interaction with other phenolic and nonphenolic materials and the volatile fraction of the wine matrix remain to be explored.

Different maceration techniques applied during red wine production affect the rate, quantity, and sometimes the chemical composition of the phenolic compounds that end up in the wine. Control and understanding of the factors that modulate phenolic extraction and retention into wine during maceration should ultimately allow the winemaker to adjust maceration variables to meet a given wine style sought and/or to comply with commercial specifications.
