Effects of bentonite treatment on the composition and properties of red wines

From the results of preliminary trials on bentonites employed for the present work, the products commercially available so far show quite diversified properties. On the one hand this make difficult an exact prediction of the effects caused by a given bentonite; on the other it gives the opportunity of selecting the bentonite most suited to the different application purpose. The processing of red wines with bentonites aims first of all at their stabilization by the removal of the phenolic complexes of high molecular weight. However, the above phenolic fraction, of subcolloidal type, represents quite a small percentage of the total phenolic content and the range of the absorption properties of bentonites is much larger; therefore the effects on the wine composition turn out to be very complex. One of the class of compounds most sensitive to the bentonite action is that of anthocyanins: the immediate consequence of a drop in their concentration is a decrease in the colour depth and the shift to less bright hue. At any rate the reduction in the dyeing intensity is not directly proportional to the percentage of absorbed anthocyanins. In fact their coloured modifications present in wines seldom amounts to more that 30-40% of the total and, besides, the colour of a red wine, even young, is determined largely due to coloured complexes of the anthocyanins themselves with flavans molecules. The latter condensed flavanoids are surely much less absorbed on bentonite. Phenols other than anthocyanins are absorbed to a much lesser extent, even though a reduction in their content is of some consequence since it affects the sensorial characteristics of the treated wine. Therefore the treatment of red wines with bentonite is conductive to a twofold result. First a reduction in colour depth, sometimes necessary in the case of rose or light red wines. Second, a reduction in the flavanic content of certain wines effects unduly tannic and of course taste; the latter certainly is a rewarding accomplishment