Barrel aging reactions during

Anthocyanin molecules are not very stable, so their concentration in wine drops sharply during the first few months of barrel aging. They disappear completely in a few years, although the wine remains red. This decrease is due to combination reactions with various other compounds in the wine, especially tannins, as well as breakdown reactions. 

In wine, this type of reaction occurs at the same time as the heterogeneous polymerization of the procyanidins (Section 6.3.7), as a result of the controlled oxidation during barrel aging, when traces of ethanal are produced by the oxidation of ethanol. The color of the wine becomes more intense and changes tone, becoming darker after a few months in the barrel. 

During aging Reactions with ethanal should be promoted by 1) using oak barrels that allow oxygen to penetrate and oxidize the wine, as well as release ellagitannins, which act as oxidation cofactors, 2) micro-oxygenation, or... 

As shown in Table 13.8, these reactions occur spontaneously in barrel aged wines, as they are always sufficiently well aerated. Regular aeration during racking of wine aged in the vat may... 

Traditionally, large oak barrels are used to facilitate the diffusion of oxygen. This is assumed to play a major role in the many chemical reactions occurring during aging. Oxidation reactions promote desired changes in wine phenolics (e.g., anthocyanins, flavonoids, and tartaric esters of hydrocinnamic acids) as well as oak phenolics extracted from the... 

Stabilizing reactions that affect wine colour and clarity, structural changes in the phenolics and new aroma formation all take place during oak wood aging. None of these reactions occurs in tanks or bottles, which are inert, do not interact with the wine, and do not allow the controlled oxidation that takes place in oak barrels. 

Several chemical reactions that happen in the barrel during aging can also affect the final volatile composition of wines. Among these reactions is found the oxidation due to the entry of oxygen across the pores of the wood, which modify both the wine volatile compounds and those extracted from wood. On the other hand, microorganisms, proceeding from the wine or from the barrel, especially lactic bacteria and yeasts, can produce important volatile compounds from a sensorial point of view, like vinylphenol and vinylguaiacol (Jarauta et al. 2005). 

Chemical reactions occurring during barrel and bottle aging... 

During the barrel and bottle aging of wine, many oxidative reactions modify the structures of the original procyanidins. Phenolic compounds in wine may be fractionated into four classes (Section 6.4.6) that have characteristic reactivity to gelatin (Table 6.9). According to the percentage of each of these classes in a given wine, it is... 

Chemical or enzymic reactions occurring after fermentation, during aging of the wine in vat, barrel and bottle. 

From this moment on, the wines receiving the additional fortification will age in the absence of a yeast film, without flor yeast activity. Only physicochemical phenomena occur. During the aging process, some of the substances responsible for the fruity character in the wine are oxidized by oxygen. The barrel wood also plays a role in the oxidation process. Its texture acts as a type of tissue of semi-permeable membranes. The reactions involved in these phenomena are slow and poorly understood. Basic wood substances are extracted and oxidized. 

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