Maturation of Wine
Changes in Wine Composition during Maturation
Many reactions occur during the maturation phase which lead to significant changes in the composition of the wine. Many of these changes are subtle and, in some cases, so small that their impact on the sensory properties of wine is not noticeable. On the other hand, certain reactions have a noticeable effect on the various sensory attributes of wine, and they play a significant role in wine maturation. During maturation the grape-derived aromas fade, more complex and pleasing aromas develop, and changes in taste and mouthfeel occur too. Astringent and harsh tastes are replaced by smoother, rounder tastes. The various aroma and taste components integrate, yielding complex, rich, and delicious wines.
Taste and Mouthfeel
With proper maturation, the wine becomes mellower and smoother, and acquires a richer mouth feel. Many compositional changes contribute to the improved taste. The important changes include polymerization of phenolic compounds and reduction in acidity. Tannins in young wines contain many short tannins that contribute unpleasantly aggressive, green, stemmy characters.
Bouquet
There is generally a distinction made between aroma and a wine's bouquet but often these two terms are used interchangeably. Aroma refers to the smells unique to the grape variety and are most readily demonstrated in a varietal wine - such as lychees with Gewurztraminer or black currant with Cabernet Sauvignon. These are smells that are commonly associated with a young wine. On the other hand, wine bouquet results from the winemaking process of fermentation, maturation, and aging from chemical reactions among acids, sugars, alcohols, and phenolic compounds that form of new aromas. These can include honey in an aged Sauternes or truffles in a Pinot Noir.
Color
Generally, during the process of maturation, the most obvious change occurs in the color of the wine.
Effect of Oxygen on Red Wine Color
In young red wines, the bright red (with purple tint) color is due to monomeric anthocyanins, or free anthocyanins, which are extracted from the skin during fermentation. Oxygen (from air) plays an important role in the condensation reaction between anthocyanins and tannins, which results in the gradual loss of free anthocyanins and the formation of stable polymeric (anthocyanin tannin) pigments.
Effect of Oxygen on White Wine Color
Unlike red wines that lose their color, white wines tend to enrich their color over time, shifting from a lightyellow or greenish tint color to a deeper yellow color. A brown color is normally unwanted because this indicates oxidation in white table wine. Brown color is normally measured at 420 nanometers (nm) in white wine (du Toit et al., 2006). Brown coloration can be induced by enzymatic oxidation (Section 17.1).
Oxidation
Oxidative changes are an important part of wine maturation (Chapter 17). The rate of oxidation depends on pH, temperature, concentration of dissolved oxygen, and the phenolic composition. Oxidation is greater at high pH and high temperature. Wine maturation can be accelerated at higher cellar temperatures; however, such treatment can have an adverse effect on the quality of a wine.
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