Far more than a mere storage container, a wine barrel is an active agent in defining the character of a wine. The most common material for barrels is oak, a flexible yet strong wood that is naturally waterproof yet allows the entry of oxygen into the wine. This assists with maturation process, softening texture and adding some of the aromas that characterize wine such as vanilla, toast, and leather. The type of oak, age of the barrel, and toast level are all important factors in the effect a barrel has on the wine within.
The two main types of oak used are American and French. Since American oak has larger pores, wine soaks into the wood more quickly, absorbing flavors faster. American oak contributes more aggressive tannins but a wider variety of flavors including chestnut, cedar, tobacco, dried fruits, and spices such as cumin, pepper, and licorice. French oak, on the other hand, lends notes of vanilla, coconut, clove, black pepper and cinnamon. It also contributes softer tannins that lend a touch of elegance to the wine. By having finer pores its flavors are transmitted more slowly.
Another important factor is the age of the barrel used. For example, a new barrel usually releases 50% of its organoleptic properties (its influence on flavor and texture etc.) on the first use, 25% on the second use, and less thereafter. As a barrel is used it becomes more neutral and has less impact on the wine it contains.
Toasting is also a crucial step in the manufacture of a barrel, because it modifies the structure and the chemical composition of wood, in turn affecting the flavors of the wine. Basically, toasting causes a decrease of the astringency in the wood, matched with an increase of aromatic substances, ones that already exist in the wood and new ones formed through exposure to heat. Toasting ranges in four degrees or levels from light to heavy. The process takes 15 to 60 minutes, with temperatures ranging from 250° F for light toast to 475° F for heavy toast. In order to create a high-quality barrel, the toasting process must be uniform and controlled.
The degree of toast in a barrel has a profound impact on the flavors of a wine. Soft or light toast gives a wide array of aromas. Most pronounced are coconut, cream, and white chocolate. Used alone, however, this light toast can sometimes result in an unpleasant, resinous quality. Medium toast is the most commonly used since it provides good balance and complexity. While the coconut notes (lactones) decrease, other volatile substances increase, such as vanilla, caramel, coffee and bread. On the palate it is characterized by sweet and spicy notes combined with vanilla caramel and milk chocolate as well as toast, smoke, spice, and leather. High toast or medium plus, results in more pronounced spicy and smoky notes, graffito, dry leaves, gunpowder, and black chocolate. Very high toast imparts intense, powerfully smoky notes. While this goes well in certain wines, it risks giving the final product an overly roasted character.
When choosing barrels, wine makers consider both the type of wine to be aged and the type of wine that they are expecting to obtain. Often they do not stick to one type of barrel but “play” with different toast levels, giving the final wine more complexity and diversifying the aromas and textures.
This interplay of wood, flame, and time in barrel aging is a fluid and fascinating process. Done well, it results in a world of flavor and complexity—a transmutation and tempering of fruit into a wine with depth, nuance and unique character.
– Sole Clavería