Wooden Wine Barrels
What does wood aging do to a wine? There are three aspects to consider, the wood it is made from, the size and shape of the cask, and the age of the cask. Oak is the preferred timber because of its strength and relative lightness, its cellular structure and it is the taste components it contributes to wine.Aging wines in small oak barrels accomplishes several things. Barrels add oak nuances and flavors, similar to the spicing in a food dish. Thus, the choice of a barrel is very important relative to size, source, degree of toasting, and the cooper's barrel-making technique. There needs to be a synergistic effect between the wood and the wine.
The major factor influencing the flavor/aroma composition of oak cooperage is the heating and toasting of the staves during barrel-making. Toasting penetrates about halfway into the stave, about 10-14 mm. As the length and heat of toasting increase, there is a corresponding increase of vanilla, maple, spice, and toasty characteristics which will be imparted into the wine.
The origin of the oak used for barrels can significantly affect the flavors produced during the aging and fermentation process. French oak can impart strong aromas and flavors of spice or vanilla. American oak tends to impart stronger tannins, dill and coconut flavors. Depending on the wine's weight and intensity, it will spend from 10 months to 3 years in oak. Wine in barrels evaporates at a greater or lesser rate depending upon the temperature and humidity of the cellar. To avoid oxidation, the lost wine is replaced weekly by topping off the barrel with the same wine from another cask.
The shape and the size of the cask is another component to consider; the traditional wine barrel holds about 225 liters and was traditionally made this size so two men could easily handle it. But more importantly, it provides the optimum surface area of oak to wine. Smaller casks provide more oak-contact, but are not cost effective. Lastly, the age of the cask is an important factor. New oak contains the most flavoring compounds. As the cask is used, tannins and other substances are leached out of the wood and tartrate crystals from the wine build up on the barrel's interior, eventually causing the cask to become inert. New oak also allows for more oxidation and inserts more tannin. It also contains more softening substances from the cellulose of the wood. The best French barrels cost about $800 each, the American oak costing about half. One barrel holds enough wine for about 25 cases. Well-treated barrels can be used several times, especially for white wines. Therefore, if a winemaker decides to use a French oak barrel three times, each case of wine will cost roughly $14 more to produce or $7 more a case with American oak.