Many winemakers store and age different varieties of wine within oak barrels, as this improves the structure and body of the wine, while adding flavor from the oak. New barrels made from oak provide flavor to the wines stored therein for approximately 3–4 years, after which time the barrels become neutral. Aging wine in an oak barrel after it becomes neutral can still help to improve the wine by concentrating its flavors through the process of evaporation, which occurs by water content escaping from the barrel.
Wine structuring happens through the polymerization of tannin molecules. This process continues so long as the wine is within the barrel. Winemakers continue aging wine in an oak barrel for approximately 6–9 months to allow enough time for the wine to be in contact with the wood.
Barrels which are younger give off structure and flavor at a faster, stronger rate than do older barrels. Therefore, as the barrels themselves age, aging wine can be kept in them for longer periods of time without the oak flavor becoming too intense. American oaks release flavors more quickly than do European oak varieties.
White wines are often fermented in brand new barrels. This is because white wines can absorb all the needed influence from the barrel in the fairly short time it takes for the wine to ferment, and white wines are, in general, imparted with less oak flavor than red wines. From there, the barrel goes on to be used for red wine aging because it will give off its oak flavor more slowly, and red wines need a longer fermentation and aging period to develop all of the depth and flavor necessary.
The information above is an example based upon what we know about aging wine in an oak barrel, with respect to intensity of flavor and the time frames needed to develop those flavors. New barrels will provide flavor and structure more quickly to the wines contained therein, while barrels which are older must hold wine longer to achieve polymerization and a correct level of tannins for a quality product.
The size and age of the barrel and the style of wine desired also dictate the amount of time the aging wine must stay within the barrel. This is due to the ratio of volume of wine to surface area of the wood. To put it another way, if a barrel is small, the aging wine held within it will need to spend less time aging than the same wine would in a larger barrel. The wine in the smaller barrel achieves flavor extraction from the wood quicker than it would if the same wine was aged in a larger barrel.
Taste is the most important determining factor of how long a wine should spend inside of a barrel. Aging wine in an oak barrel is all about imparting the correct level of flavor and structure to any given wine. However, something to be aware of is the fact that once the wine is bottled, during the first year the oak flavor will mellow out a fair amount. So it is perhaps a good idea to bottle wine when it has slightly more oak flavor than one would prefer, as it will diminish over time within the bottle. It is a trial-and-error process for many winemakers in the beginning stages of this craft.
It is also of note that many wines are aged inside of the barrels for 2–3 years, such as full and medium-bodied wines. If you were to instead age that wine in a 3 liter barrel, the same flavor result could be achieved in only a few months time.
When aging wine in an oak barrel, one of the most important things to remember is to remove a portion of the wine prior to placing the rest within the barrel. This saved portion should be stored in either stainless steel or glass so that no oak flavor is imparted. Once your wine is finished aging in the oak barrel, if you feel that the taste is too strong, you can simply blend some of the non-oaked wine back in with the finished wine to achieve the perfect flavor balance.