Only one type of wood has been tried and true for construction of wine barrels over thousands of years of wine-making: oak. Although cherry, walnut, chestnut, pine and redwood can be made into barrels, and some have been used for making wine, only oak seems to have the right relationship with the grape to satisfactorily age it and enhance its flavors. Oak is composed of chemical compounds like tannin that give wine its vanilla, tea and tobacco-like characteristics without being overpowering.
Types of Oak and Small Barrels
In the vast majority of cases, wine barrels are made with one of two types of French oak (Quercus robur or Quercus sessiliflora) or with American oak (Quercus alba). The French oaks are used primarily to make Bordeaux barrels, which hold 59.43 gallons of wine. They are are used for many types of wine, but for cabernet sauvignon, merlot and Bordeaux in particular. French oak is also used to make Burgundy barrels, which hold 60.2 gallons, and to age pinot noirs and Burgundies. American oak barrels are made in both sizes and hold all types of wine.
Location of Oak
The most prized oak trees grow in the French forests of Tronçais, Vosges and Nevers, where the forests are cool and dry. This type of environment produces trees with tight rings, which allow the flavors of the oak to come out gradually as the wine is aged. The best American oaks for wine barrels are found in similar climates in the forests of Minnesota and Iowa. Oaks used for wine-making are also grown today in Canada and Hungary.
The other important element that goes into barrel-making is the craftsmanship of the barrel-maker, or cooper. When American oak was first being used to make barrels, it was thought that the oak wasn't the right quality, as it imparted off-flavors into the wine. Rather, it was the way that the barrels were constructed. Americans were used to making whiskey barrels, which utilized wood dried in a kiln, and sawed staves. French coopers instead let their wood dry outdoors for up to two years and split their staves by hand, which gave the wine more flavor. Once Americans started to use the French techniques with their native trees, they produced barrels that were just as good for wine-making as the French ones. Additionally, wine staves have traditionally been bent over steam in the United States, while they're bent over fire in Europe when making barrels. Fire produces more toasted notes in the wine, and many American coopers have recently switched to the fire method.
Hogshead Barrels and Puncheons
Bordeaux and Burgundy barrels are considered "small barrels," while hogshead and puncheons are much larger. A hogshead barrel, which was the typical barrel in the Middle Ages, holds 79.25 gallons of wine. A puncheon comes in both this size and a whopping 132.08 gallons--over twice the size of Bordeauxs and Burgundies! In general, because contact with the oak is smaller by volume for these wines, winemakers use hogshead or puncheon barrels if they want the oaky flavors to be less pronounced (as in, for example, Sangiovese and some pinot noirs).
Fermenting vs. Aging
Wines are generally aged in barrels but fermented in stainless steel tanks. The only exception is for some wines, like chardonnay, whose flavor improves when fermented in oak. However, the extra step of fermenting in barrels is not necessarily what adds the rich vanilla flavor of some chardonnays typical to California; usually these flavors result when the wine has instead been fermented in stainless steel and then aged in oak (or aged longer). Generally, red wines spend a longer time aging in oak, as delicate white wines are overpowered if they spend more time in wood. The length of time that wines---red and white---are aged in barrels depends on the style of wine as much as regional preference.