Wine makers and wine drinkers love to talk about oak. And given that oak-use is incredibly complicated, it is not surprising. Oak barrel fermentation, aging in oak, the flavors that oak imparts, the amount of oxidation you get through the porous oak barrels, the type of oak that is used – American, French, Slavonian – and the size of the barrels not to mention the discussions of how the barrels are made and who makes them. It is all fodder for both professionals and enthusiasts.
Let’s break it down a bit first. The first use of oak is said to have been a Roman “discovery.” In ancient times, in Mesopotamia and Greece, there are written accounts of people using palm wood to transport wine. However, because palm wood is hard to bend for barrel-making, the Romans had begun using clay amphorae – until they spread to Gaul in what would one day become France. There they noticed the Gauls using oak barrels held together with metal bands to transport beer. It became obvious to the Romans that transporting wine in wood rather than clay would save a great deal of wine from destruction.
Oak was particularly favored for barrel making because it was plentiful in Gaul and was relatively easy to bend to the barrel stave shape and could be toasted to impart certain flavors and textures to wine. Over a short period of time, the Romans realized that oak made wine softer and smoother and more aromatic, and the rest as they say, is history.
These days, oak barrels are made in cooperages, and each cooperage imparts its own unique character to its barrels. The staves are made with freshly cut or split oak beams. American oak is less dense and can be cut to size while French oak, which has a tighter grain, must be split. In the most traditional (aka, “best”) cooperages, the staves are left out in the weather for a few years to “condition.” A modern cooperage will kiln dry the wood. Then the staves must be heated to bend them into the characteristic shape for a barrel before being roasted over fire for the desired amount of “toast”. The amount of toasting is very important because it determines the flavors that are imparted to the wine. The darker the toast, the more coffee, burnt sugar and even smoky flavors. Less toast offers vanilla, coconut and baking spice aromas. Furthermore, there are differences in the flavors imparted by French and American oak, with French oak naturally having more hazelnut and smoky aromas and flavors while American oak imparts coconut and butterscotch. A good cooperage will be able to work with the vintner to determine what exactly what type of oak and toast the wine needs and will be able to make the barrels to exacting specifications.
So what does oak do for wine? It is slightly different for white and red wines. In white wines, oak tends to lend a more delicate flavors and fewer tannins. The oak itself has tannins that bind with the proteins in the wine, so whites do not become more tannic with oak fermentation or aging. Red wines on the other hand, already have tannins that have bound with the proteins in the wine. That means that non-neutral oak generally imparts more tannins to red wines than they have naturally. So, in addition to the vanilla / caramel / butterscotch types of flavors in American oak and the more coconut / hazelnut / smoky flavors in French oak, red wines tend to become more structured in oak barrels. Initially at least. Over time, oak is permeable to small amounts of oxygen. This slow process of oxygenation allows the tannins in red wine to form chains and become smoother and more textural, rather than drying.
Aging wine in oak is expensive for many reasons – the barrels are costly, they allow the wine to evaporate and need to be topped up regularly, it is hard to keep the barrels clean, they need more careful handling in the winery and so forth. So, most wines that are stored in oak are high quality wines. However, there are certain less expensive wines that boost oak flavors in the wine by adding oak chips or staves to wine – and these wines are often over-oaked and are dominated by the oak flavors rather than the flavors of the grapes.
It has been my observation that some people love oak flavors in wine – hence the popularity of California Chardonnay for example – and some people love wines with no oak – like Chablis much of the time. It is something you, dear reader, will have to disambiguate for yourself. Either way, cheers!