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Dehydrated yeast cells at variable concentrations were used as fining agents to decrease the color of white wines with two different degrees of browning (0.153 and 0.177 au, measured at 420 nm). Both wines showed a linear decrease of browning with increasing yeast concentration. However, in terms of efficiency, the yeasts exhibited a higher color lightening at greater concentrations acting on the darker wine. This suggests a preferential retention of some types of yellow-brown compounds that could increase their concentrations at the higher degree of browning. To confirm the role of yeast cell walls in the retention of browning compounds and to evaluate their potential use as fining agents, they were applied at variable concentrations to a browned wine (0.175 au). The cell walls were found to be the active support for the adsorption of browning compounds, but their efficiency was much lower than that of an equivalent amount of the yeast cells from which they were obtained. Finally, HPLC determinations of low-molecular-weight phenolic compounds showed flavan-3-ol derivatives to be significantly retained by both yeasts and their cell walls.

White wine was subjected to several fining treatments using baker's yeast at concentrations of 0.5, 1, 2, 3, 4, and 5 g/L. At all these concentration levels, the yeasts decreased the color of the wine in different degrees. The wine samples treated with the higher yeast concentration were subjected to analysis of phenolic compounds by HPLC and found to exhibit significantly decreased contents of vanillic, syringic and c-coutaric acids, and procyanidins B2 and B4, and colored compounds eluted at high retention times. The efficiency of the yeast-based fining treatment (1 g/L) was compared with traditional treatments such as those involving the use of activated charcoal or PVPP, which were employed at the usual concentrations in Sherry winemaking. This yeast treatment was found to provide results similar to those of the activated charcoal treatment in terms of A(420). Likewise, significant differences in the degree of retention of various phenols were observed among the three treatments compared. Finally, the wine samples obtained with the different treatments were subjected to a sensory panel. All the wines were found to exhibit improved color, aroma, and flavor with respect to the untreated samples, although the treatment using yeast at 1 g/L provided the best results in terms of aroma.

Results show that the variables studied in this work increased to a greater extent in a 1st stage (wine exposed for 4 y to daily temperature fluctuations) than in a 2nd stage (wine held at a constant temperature of approximately 17°C up to the 14th year). To study aging under more controlled conditions, a 2-stage laboratory experiment was carried out (the 1st ranging from 15 to 30°C, the 2nd at 30°C). The results revealed an important acceleration in the aging of this type of wine. However, aroma and flavor properties were slightly affected, probably because of the higher temperature maintained during the 2nd stage.

The composition in hydroxybenzoic and hydroxycinnamic acids, hydroxycinnamic esters, tyrosol, syringaldehyde, and flavan-3-ol derivatives of three different types of sherry wine obtained by aging of the same starting wine under different conditions was studied. So-called “fino” wine was obtained by biological aging under flor yeasts, “oloroso” wine by oxidative aging, and “amontillado” wine by a first stage of biological aging followed by a second oxidative step. On the basis of the results, the wines subjected to oxidative aging exhibited higher phenol contents, in addition to scarcely polar compounds absorbing at 420 nm that were absent in the wines obtained by biological aging. Taking into account that flavan-3-ol derivatives play an important role in wine browning, a model catechin solution was inoculated with flor yeast which, contrary to the findings of other authors in the absence of yeasts, formed no colored compounds. This different behavior may account for the resistance to browning of pale sherry wines in the presence of flor yeasts. Keywords: Wine browning; biological aging; phenolic compounds

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Contents of hydroxybenzoic and hydroxycinnamic acids, hydroxycinnamic esters, and monomeric and dimeric derivatives of flavan-3-ol during biological aging of dry pale sherry white wine were measured and compared between wine without aging and wines in five different stages of aging. The results show a significant decrease in the levels of vanillic and ferulic acids, catechin, epicatechin and procyanidins B2 and B4, as well as an increase in those of syringic acid and procyanidin B1. According to the changes observed in polyphenol contents and the absorbance data obtained at 420 nm, sherry-type wines seem to be protected from excessive browning during biological aging mainly as a result of the partial removal of flavan-3-ol derivatives, besides the effect of protection from air contact carried out by the flor yeasts growing on the wine surface. Keywords: Phenolic compounds; aging; browning; sherry wine