Posibilidades tecnológicas de las paredes celulares de los orujos de uva como agentes afinantes durante la vinificación

Abstract

Fining wine is a technique used in oenology to eliminate unwanted wine components that negatively affect their quality. The fining techniques, commonly called clarification techniques, usually involve the addition to the wine of a reactive or adsorptive material that eliminates or reduces the components responsible for undesirable properties of the wines. In general, they are not considered additives but coadyuvants since they are designed to be eliminated from the wine treated as part of the fining process. However, in recent years, problems with some proteins (bovine spongiform encephalopathy related with bovine gelatins, the allergenic nature of other proteins such as casein or albumin) have led to a search for alternatives, among them proteins of vegetable origin (legumes and tubercles). Attempting to solve this problem, an option that could have an important enological application would be the use of cell walls of vegetable origin, especially from the grape marcs, since this material shows a great affinity for tannins and other wine components, and could be interesting when looking for the reduction of the astringency of the wines. For this reason, the objective of this doctoral thesis is to determine if the cell walls of the grape marcs, more or less purified, can be used as a new material for fining red and rose wines, in order to reduce their phenolic load, tannins and other substances that may affect the quality and safety of wine (biogenic amines, ochratoxin A and some minerals). Based on these premises, a series of experiences has been designed to determine the effect of cell walls obtained from grape marcs, and applied at different doses (4, 6, 8,10 and 13 mg/mL) as fining agents and to compare results with respect to those observed with the commercial finning agents normally used in winemaking. The effect of different contact times with the wine (90 min and 3, 5, 10 and 21 days), different type of contact (stirring or stand) and the possible occurrence of a varietal effect have also been studied. To conduct the study, the cell walls or the purified grape pomace were made to interact with the wine and, after the established contact time, the wines were evaluated, analyzing their chromatic parameters, their content in anthocyanins and tannins and the content in volatile compounds. Also, wines were spiked with biogenic amines and ochratoxin A to study the potential of this material for the reduction of these unwanted wine compounds. In addition, it was also studied if the proposed fining material was able to remove minerals and enrich the wines with polysaccharides. The results showed that the purified cell walls extracted from grape pomace obtained after the fermentation maceration stage of a red wine, have a high capacity to retain phenolic compounds, and the vinification conditions from which they were obtained do not seem to play a determining role. Of the two varieties tested, the cell walls of Monastrell retained more phenolic compounds than those of Cabernet Sauvignon and both more than the commercial affinity compounds normally used. Since the purification of the cell walls of pomace is a laborious process, a simpler process was tried, using purified pomace directly in the wine. The results showed that this purified grape pomace also showed a high retention capacity for the phenolic compounds, in fact, a dose of 6 mg/mL and 5 days of contact could be enough for a significant reduction of wine tannins, which would reduce the astringency of the treated wine without a significant loss of color. In addition, they were effective in the reduction of ochratoxin A, histamine and the minerals calcium and potassium. As a negative part is that the content of aromatic compounds in wines was slightly reduced. To strengthen further this proposal, another trial was carried out using pomace of different varieties (red and white grape varieties), concluding that all of them showed a high potential as fining agents, although the pomace from the white variety reduced the phenolic compounds to a lower extent than those of the red varieties, but they provide a greater degree of turbidity reduction. Finally, its application to a rosé wine was also studied, determining that the use of the purified pomaces is comparable to that of the commercial fining agents used in this wine. As a final conclusion, purified grape pomace can be a product that competes with the commercial agents that currently exist, without many of their problems. It is important to indicate that these results must be completed with studies on an industrial scale.