VINIFICAZIONE IN ROSSO: INFLUENZA DEL ¿GRAPPOLO INTERO¿ SULLE PROPRIETÀ CHIMICO FISICHE DEL VINO

ABSTRACT The ¿whole bunch¿ red winemaking, characterized by the presence of stems during the fermentation, is an oenological practice historically known and still used in some wine regions. The technological progress in Enology led to a removal of the stems from the general red winemaking process, but during the last few years there is a strong return towards the use of this technique. In addition, several scientific studies have recently shown many positive aspects and applications of this particular technique. From the compositional point of view, stems contain water, which is released in wine causing a slight lowering of the alcohol content. Mineral substances are present, with the highest content being represented by potassium: it is released during the fermentation/maceration period and it can bind in wine with tartaric acid forming potassium hydrogen tartrate (KHT), tending to precipitate. Stems have also important concentrations of flavan-3-ols monomers and proanthocyanidins, the flavan-3-ols present in higher concentrations are (+)-catechin and (+)-gallocatechin. By making a direct comparison between traditional vinification and "whole bunch" wine production technique it is possible to understand both the common points and the important differences that exist, the latter are crucial when it is necessary to decide whether to leave a percentage of stems in the winemaking lot. In particular, "whole bunch" winemaking is more laborious as regards to some cellar operations due to the voluminous size of the stems; for instance, punching downs will require a greater attention and a longer time in order not to lacerate the stems and at the same time carry out an effective work. The same applies to the racking: the presence of whole fermented bunches makes it essential to use tanks provided with systems that allow the rapid release of the liquid, thus avoiding clogging; moreover, in this phase the removal of the skins composed for the most part of whole bunches turns out to be the most difficult and laborious operation of the whole process conducted in the presence of stems. From a compositional point of view, wines obtained from the "whole bunch" technique in experimental studies are richer in polyphenols, have a more marked astringency, higher pH and a lower titratable acidity. In conclusion, this technique is useful to produce wines obtained from grapes with a modest polyphenolic profile and for the production of aging wines, potentially increasing color stability and resistance to oxidation.