Utjecaj bistrenja bentonitom tijekom alkoholne fermentacije na proteinsku stabilnost, arome, fenole i senzorsku kvalitetu vina Malvazije Istarske

The aim of this study was to investigate the influence of different conditions of bentonite fining during fermentation - the moment of bentonite application, application method, bentonite preparation method, application of oenological tannins in combination with bentonite, must temperature during fining, bentonite dose, and bentonite type applied - on the required dose of bentonite to achieve protein stability, standard physico-chemical quality parameters, the concentrations of phenols and volatile aroma compounds, and sensory quality of Istrian Malvasia wine. The most significant reduction of dose was achieved by applying bentonite in the last third of the fermentation period. The preparation of bentonite in deionized water slightly contributed to the reduction. The application of oenological tannins lowered the total dose of bentonite required, but the combination of tannins with bentonite in fermentation did not achieve a synergistic effect. Bentonite fining during fermentation significantly affected physico-chemical composition of the produced wines: it preserved higher concentrations of hydroxycinnamyltartrates, while a positive effect on the preservation of the amounts of key fermentation aroma volatile compounds, such as volatile fatty acids and esters, was particularly significant. The application of tannins contributed to the preservation of higher concentrations of total acidity, total phenols, and hydroxycinnamoyltartrates. The addition of tannins, higher temperature during fining, and the application of higher dose of bentonite in fermentation had an additional beneficial effect on volatile esters. Particular types of bentonite showed more significant positive effects than others. Bentonite fining during alcoholic fermentation showed a clear positive effect on the sensory quality of the investigated wines. Various positive effects were more pronounced in partially fined wines after fermentation, while additional fining after fermentation reduced or nullified them. The effects of particular treatments were not of equal intensity or even sign in different years of research. Further research should focus on identifying the possibilities to limit the adverse effects of final fining with bentonite after fermentation, as well as on elucidating the influence of physico-chemical composition of grapes as raw material on the efficiency of fining during fermentation.