**1. Introduction**

Red wines are a very complex hydroalcoholic matrix, with a wide variety of compounds extracted from grapes and with a high quantity of metabolites released by yeast during the fermentation process. Alcohol and water represent most of the wine composition, however, small quantities of other compounds are the main responsible for the wine color, aroma and flavor.

The color of red wines is a very important feature, we cannot forget that it is the first attribute to be perceived by wine consumers and is directly associated with its quality. Moreover, as stated by Peynaud [1], color also provides information about variety, type of elaboration, defects, the type of aging and the conservation during storage.

The typical normal sequence in wine tasting is to view, smell, and taste. The visual appearance, and color in particular, may have such as impact that it may also influence on smell, which, in turn, may impact on taste. As an example, Morrot et al. [2] conducted a tasting session where three wines were presented to a tasting panel, a white wine, a red wine and the white wine colored red by an odorless and tasteless colorant. The white wine was described using normal terms associated to white wines while the same wine colored red was described using typical red wine descriptors. Also, other experience showed that the aroma description of a wine changed if the tasting was conducted in opaque glasses. The most important conclusion is that the color of the wine plays an important role not only in appearance but also in defining wine attributes and quality [3, 4].

Given the importance of color on wine quality and consumer appreciation, viticulturists, winemakers and scientists dedicate a lot of attention to the grapes (with the enormous polyphenolic variability that may be present in grapes, influenced by ripening, genetic, or environmental factors) and the winemaking process (alcoholic and malolactic fermentation), since wine color starts in the grapes but develops in the winery.

Two types of phenolic compounds are paramount in wine color. The most obvious significant compounds are the anthocyanins, that provide the red color of wines, but also the flavan-3-ols are very important compounds, since they assure the long-term wine color.
