There is a nice article in The Wall Street Journal that explains the importance of oak barrels in giving wine some of its distinct flavours. Here are a couple of paragraphs from the article.
“So where do these flavors come from? Anyone who has walked through a vineyard, particularly after a heavy downpour, may detect aromas one could identify as floral or fruit, but they certainly won’t find smoky bacon or coconut.
“The answer actually lies in the forests of France, Hungary and the U.S., where sessile, pedunculate and white oak is grown for the construction of barrels. It is these oak barrels, comprising pieces of wood called staves and held together by iron or chestnut hoops, which are used to mature wine.
“The benefit of aging wine in oak is that new oak softens the bitter flavors in wine while also imparting its own signature notes that help develop the character and multiflavored composition of the wine. The most obvious example is vanilla and spice for red wine and toast, butter, coconut and nuttiness for white wine. Thus, if someone puts their nose into a glass of red Bordeaux and smells pencil shavings, it isn’t as strange as it sounds—it comes from the wood.
“As a thumbnail guide, American oak imparts powerful aromas of sweetness and butterscotch and is rich in coconut. French oak has more tannins, which, when combined with the natural tannins found in the grapes, imparts a more nuanced, structured and dry character to the wine. Hungarian oak can impart a soft, creaminess on the palate of a wine.
“French oak is still regarded by many as the best for aging wine, particularly those trees grown in the Forest of Tronçais in the department of Nièvre. The forest was originally planted by Louis XIV’s minister Jean-Baptiste Colbert, who envisaged it as a valuable source of building material for royal ships.
“The length of time a wine is aged in oak barrels depends on the style of wine the winemaker wants to create. In the regions of Bordeaux and Burgundy, it can be anywhere between 12 and 18 months, while in Spain, it can be more than two years. A lot depends on the grape variety. Those that produce more powerful wines benefit from the wood, while more delicate wines don’t. However, it is important to note that a wine that imparts strong oak characteristics may not necessarily have been aged in oak. It could have been flavored by the use of oak chips, which are submerged into a stainless-steel vat. This method is mainly used to alleviate cost.”