Aside from the grape vine, the oak tree is the most important plant associated with winemaking. Not only is oak wood used in barrel making for wine storage, but cork trees are also a species of oak.
OAK FOR BARRELS:
Though many different types of wood have been used to make wine barrels, it is widely accepted that oak offers the most appropriate wood for aging wine. However, wine was originally stored and transported in wood, not bottles, simply because this was the most efficient and least risky method. Over time, it was discovered that aging the wine in oak was more than just a practical option. Oak has many substances and chemical compounds that are extracted by the wine during the aging process and impart interesting flavors and added complexity to it. Oak barrels provide the minimal exchange of oxygen necessary for the wine's evolution, yet the wood's own tannins actually protect the wine from over-oxidation.
Oak trees used for wine barrels are cultivated mainly in France and the US. Though many other countries in Europe have oak forests, either they have not been as well protected, maintained and forested by the government or the quality of the oak is perceived to be inferior to that found in France and the US.
French forests account for approximately 40% of the European Union's forests. Thanks to excellent forest management (anyone can appreciate the impeccably straight rows of trees), the French have ensured a surplus of quality oak for cultivation. There are many renowned forests in France, most notably Loire, Allier, Nevers, Limousin, and Vosges. Within each there are numerous quality levels.
Barrels can completely alter the flavor and quality of the wine if not up to par, but if the right marriage of flavor and style is achieved, oak aging can accentuate and augment the existing flavor profile of a wine. Quality is judged by how finely grained the oak is, how it is split and how predominant the wood tannins are. French oak tends to be more finely grained and therefore less porous which results in limited exchange of wood tannins to the wine. Most significantly, French oak staves are made by splitting the logs along the grain, a very time consuming process that results in better wood for barrel making. French oak gives flavors that are subtler - more like the fruit flavors of grapes. French oak has long been considered the ultimate for barrel production because it imparts subtle flavors of vanilla with little or no harshness.
American oak is becoming more popular mainly because it is less expensive than French oak and makes barrels of similar quality, though there is still a healthy debate about which is better for aging wine. In American cooperages, the staves are usually sawn, and not necessarily along the grain. The oak trees used are generally not as fine grained as well. This can mean bolder tannins and more powerful vanilla, coconut and even cinnamon flavors. These flavors are accentuated in all barrels through the process of toasting during cooperage. Some producers use a mix of French and American oak barrels and/or a mix of different degrees of "toastiness", blending the wines after maturation. American oak forests are found in both northern and southern states such as Wisconsin, Minnesota, Oregon, Kentucky, Tennessee and the Carolinas. More barrels of American oak are sold today than French oak.