Production and aging of wine in the small oak cooperage

Wines & Vines, March, 2001 by Richard H. Graff, Andre Tchelistcheff

Most of the other chemical reactions during aging are greatly influenced by the oxygenation, redox potential and other effects which depend upon the porosity of the wood and the surface-to-volume ratio of the barrel.

As regards the anthocyanins, these reactions include: demethoxylation (either by precipitation of the most methoxilated compounds or by demethoxylation of the molecules), condensation--the formation and subsequent precipitation of colloidal coloring material, and hydrolysis of the glucosides which introduces into the wine a small amount of reducing sugar (in the order of 1 g per liter). This sugar causes additional fermentation and prevents a rapid biological stabilization of the wine.

In the case of leucoanthocyanins, an important reaction is the polymerization by oxidation of leucocyanids into tannoids. This would contribute to the hardness and astringency of the wine were it not for the fact the tannoids are oxidized into insoluble substances at a faster rate.

Most of the above reactions (and many others as well) will eventually occur no matter what size cooperage is used, but they occur more rapidly and with better effect in small cooperage. In large puncheons or tanks it is not economically feasible to allow the wine to age the length of time necessary for it to stabilize and precipitate naturally. Thus, in order to make a stable and drinkable wine in a reasonable period of time, the winemaker is forced to treat the wine drastically with heavy finings and numerous filtrations. This results in a physical stripping from the wine of the substances which produce quality, and the end product is thin and shallow, with none of the classical complexity or richness associated with fine wines. These observations apply both to red and white wines.

Biochemical. During the primary fermentation of white wines the tannins extracted from the wood, especially new wood, tend to slow the fermentation because of their inhibitory effect on the yeasts. This is a beneficial effect which helps to keep the temperature down and which protects the grape aroma and flowery character of the new wine.

The aging of wine in small cooperage rather complicates the problems associated with the malolactic fermentation. There is, first of all, some irregularity among the various barrels due to slight differences in tannic substances from the wood which inhibit, to varying degrees, the growth of the malolactic bacteria; and secondly, there are differences in temperature among the barrels resulting from the irregular cellar temperatures in which the barrels are likely to find themselves.

This problem is combated effectively in Bordeaux by leaving the barrels in the warmest place, viz. the ground floor of the winery, during the first year. The bungs are left loose and the barrels are topped frequently during this period in order to provide a proper environment for the micro-aerophyllic bacteria while at the same time insuring that there is never enough air in the barrels to permit the acetobacter to take over. This is a critical period during which great care must be exercised if the malolactic fermentation is to be successfully completed.