Oak Barrel Aging of Red Wines

Traditionally, great red wines are aged in oak barrels from the end of fermentation until bottling. The first motivation in choosing barrels was probably that they were easy for one man to handle and could also be used for shipping. It was not until some time later that their positive effect on wine development, in terms of color, clarity and flavor, came to be appreciated. However, the use of barrels involved a major financial commitment and entailed risks of microbial contamination, as well as the likelihood of communicating organoleptic faults to wine. For these reasons, the practice of aging even high-quality red wines in inert vats became widespread in the 1950’s. At that time, the elimination of old barrels, responsible for moldy off-flavors, certainly resulted in improved quality. The red wines were perhaps less complex, but cleaner and fruitier. Over the past few years, a more favorable economic climate has fostered a new interest in barrel aging. There is greater awareness of the role played by oak in wine development, and a concern to adapt barrel aging to the quality of each wine. Perfect control of the various parameters and techniques has made it possible to fine-tune the use of wood and its influence on wine quality. Firstly, clarity is easier to obtain when wine is aged in the barrel rather than in the vat, due to the smaller volume. Clarification is also facilitated by the adsorption phenomena that occur in oak. Furthermore, wine in the barrel is more sensitive to outside temperature, so the precipitation of salts, particles and colloidal coloring matter is much more likely to be triggered by winter cold. Stabilization reactions affecting color, clarity and colloids, as well as modifications in the phenol structures (softening of the tannins), also occur in wine during aging, while aromas develop. Barrel aging promotes these reactions to a much greater extent than large airtight vats, which, being theoretically inert, are considered not to interact with the wine. The phenol composition of wine is considerably modified by barrel aging, thanks to controlled oxidation. Color is intensified due to reactions between tannins and anthocyanins, as well as others involving ethanal. The free anthocyanin concentration decreases and the tannin structure evolves, as does its reactivity to gelatin. After ten months of barrel aging, wines have better color than those aged in the vat and this color remains more stable during bottle aging. The flavor is also more attractive, characterized by softer tannins. Wine also acquires aromatic complexity as a result of the odoriferous substances extracted from wood. The oaky aroma must be carefully modulated, to ensure that it b1ends harmoniously with the wine’s overall structure. Even though producers may wish to give their wines an oak character, this must not be overdone. It should never overpower the wine s intrinsic qualities. The barrels contribution to aroma and flavor may be adjusted by modifying the proportion of wine aged in oak, especially new barrels. Other important factors are the type of oak and the way the barrels are made (degree of toasting), as well as the duration of barrel aging. Three factors related to this type of aging are responsible for the wine s development: oxidation-reduction reactions, as well as volatile and non-volatile compounds dissolved from the oak.