Production and aging of wine in the small oak cooperage

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

Either a small, hand air pump or compressed gas from a cylinder can be used to create the pressure inside the barrel. If it is desired to avoid any aeration of the wine being racked, nitrogen or [CO.sub.2] can be used for pumping, and the air can be eliminated from the receiving barrel by filling it first with water and then pumping out the water using [CO.sub.2].

An electric pump can also be used for racking, but it is harder on the wine and often less convenient except in the case where all of the wine is being transferred to a large tank.

Mechanisms of Aging

The mechanisms and processes which occur during the aging of wine in the barrel can be grouped roughly into three closely interrelated categories, viz. physical, physicochemical and biochemical.

Physical. The most important physical aspect of cooperage in the aging of wine is its size, because the surface-to-volume ratio affects the rapidity with which certain processes take place and the degree to which they influence the character of the wine. Since all of the aging mechanisms are influenced to a different degree by variations in barrel size, it follows that there must be one single optimum size, one ideal surface-to-volume ratio which establishes the best balance of the wine and which most perfectly favors and develops the character of the wine during aging.

We are, fortunately, the beneficiaries of centuries of experience in this area, and we can state with some certainty that, in the great wine regions of France, at least, the barrel size of 225 to 230 liters (about 60 U.S. gallons or 50 Imperial gallons) has proven to be the most perfect. We have little reason to doubt that this size, or a size reasonably close to it, will produce the same good results in other areas. Indeed many of the best wines of California and Australia (to give two examples) have been produced and/or aged in this size cooperage.

Similarly, the optimum barrel size for cognacs and fine brandies has been established to be 300 liters (about 79 U.S. gallons or 66 Imperial gallons).

It should be emphasized that half-, quarter-, etc. size barrels are made for the purpose of storing odd amounts of wine or for breaking down a full barrel when topping. (Not that wine can't be successfully aged in these smaller sizes, it's simply that the results are not quite so satisfactory, and that much greater care must be taken, through more frequent organoleptic examinations, to avoid an imbalance in the finished product.)

The most obvious physical process which occurs during aging is the slow inhibition of some of the liquid by the wood and the subsequent evaporation into the surrounding atmosphere. There are five principal influences in this process: relative humidity, temperature, air movements in the area where the barrels are kept, the physical characteristics of the wood, and, finally, the frequency of topping.

This last is important because, where the topping is less frequent there is more opportunity for an area of wood to become dry and thus slightly more porous due to shrinkage of the wood tissue.