Sherry wines oxidative aging

Fabios, M. et ak. Phenolic compounds and browning in sherry wines subjected to oxidative and biological aging, J. Agric. Food Chem., 48, 2155, 2000. 

Sherry wines are obtained from young wines, carefully selected soon after completing fermentation. These are typically fortified by adding vinous alcohol until they reach an alcohol content of 15-15.5°. They are subsequently transferred to oak barrels before being aged. In most sherries, wine aging occurs in the so-called solera and criaderas system under the flor film of yeast. Once alcoholic fermentation is finished, races of Saccharomyces cerevisiae that can grow on the surface of the wine switch from fermentative to oxidative (respiratory) metabolism. They spontaneously form a biofilm called flor on the wine surface. 

IV. CHANGES IN THE CHEMICAL COMPOSITION OF SHERRY WINES DURING THE BIOLOGICAL AND OXIDATIVE AGING... 

Some of the most important chemical changes that occur during the biological and /or oxidative aging of sherry wines are reviewed below. 

Ortega, A. F., Lopez-Toledano, A., Mayen, M., Merida, J., and Medina, M. (2003). Changes in color and phenolic compounds during oxidative aging of sherry white wines. /. Food Sci. 68, 2461-2468. 

Zea, L., Moyano, L., Moreno, J., Cortes, B., and Medina, M. (2001). Discrimination of the aroma fraction of sherry wines obtained by oxidative and biological aging. Food Chem. 75, 79-84. 

Amontillado wines are obtained in a two-step process involving biological aging under the same conditions to those of fino wines, followed by fortification and oxidative aging as in oloroso wines. Amontillado wines are thus the oldest and most valued of the three sherry types by virtue of their acquiring a more complex flavour than the other two. 

Chemical oxidation reactions and Strecker degradation of amino acids may also result in aldehyde formation (16). These reactions are important for the formation of acetaldehyde in baked or heated Sherries. Chemical oxidation reactions catalyzed by metal ions (Cu, Fe, Mn, Mo) can result in aldehyde production in oak aged distillates (20). Such reactions may also result in the formation of oxidation products from fatty acids released during the secondary fermentation of sparkling wines (21). 

Zea, L., Moyano, L., Medina, M. (2010). Changes in aroma profile of sherry wines during the oxidative ageing. International Journal of Food Science and Technology, Vol. 45, No. 11, (November, 2010), pp. (2425-2432), ISNN 0950-5423. 

The concept of oxidative defects is quite subjective, as there are many wines where an oxidative character (rando) is considered desirable. Wines aged under a yeast bloom are a classic example, e.g. Vm Jaune from the Jura (Volume 1, Section 14.5). The yeast acts as an oxidation-reduction bnffer and prevents excessive oxidation. Vin Jaune is well known for its highly oxidized character and contains large concentrations of free and combined ethanal (Fignre 8.1) (Etievant, 1979). The same is trne of Sherry. 

Saenko, N. F. 1948. The change of the oxidation-reduction potential and the composition of wine aged under the sherry ffim (transl.). Biokhimiia vinodeliia 2,86-100... 

Certain heterocyclic compounds are also important aromatic substances in wines, such as pyrazines in Cabernet Sauvignon and Sauvignon Blanc wines (see Section 8.2.11.1.7) and both enantiomers of 3-hydroxy-4,5-dimethyl-5if-furan-2-one (sotolon), which occur in white wines, sherries and are a key component of the typical aroma of aged Port wines. The precise chemical reactions leading to the formation of bouquet substances are not yet widely known. There are two types of reactions that produce bouquet constituents oxidation, which is characterised by the presence of aldehydes and acetals (e.g. in Madeira-type wines) and reduction (such as in quality table wines after a period of bottle maturation the flavour of low-quahty wines does not improve under the same conditions, but instead maturation often leads to a loss of freshness). During wine aging, glycosides of terpenic alcohols and... 

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