History of Wine - Maturation
The practice of aging wine dates back to ancient Egypt, where it was stored in clay amphorae. The Romans, however, were the first to discover the method of storing wine in oak barrels (quercus). The genus Quercus has a wide range of varieties; one of them, Quercus suber (cork oak), is used to make the stoppers found on bottles. Oak is very durable and easy to work with, making it the ideal material for barrels.
Its wood also contains linden trees, structures that help with waterproofing. In addition, its composition is 40% cellulose, 20% hemicellulose, 25% lignin, 10% ellagitannins (hexahydroxydiphenyl esters that provide tannins to wine) and 5% of other chemical components. The effect of wood in wine is intricate and many studies have been done on the chemistry of maturation in oak barrels.
In some cases, oak wood chips (Quercus fragmentus) are used to accelerate the process of obtaining woody aromas; however, the use of these chips is regulated by the legislation of each country. Wine tends to evaporate from inside the barrel at a rate that can range between 2% and 5% of its annual volume (which means a loss of between one and five liters per year in a 225-liter barrel).
Oxygen plays an important role in the aging of wine in barrels. Since 1991, one of the methods used to allow the introduction of limited amounts of oxygen in the fermentation process has been called microoxygenation. Oxygen is essential for the preservation of the colors of red wines, since it allows tannins and anthocyanins to go through a process that is often called oxidative coupling.
Some generous wines usually go through a series of barrels (criaderas), such as fino, amontillado and oloroso, typical of the Jerez and Montilla-Moriles region. Meanwhile, wines such as vermouth are aged with aromatic herbs (such as artemisia absinthium).
Barrel aging is a process of gradual oxidation of wine. The two most common transformations that occur during this process are the oxidation of phenols and the polymerization of anthocyanins with other flavonoids that produce color and flavor. One of the most common results of this type of maturation is the formation of vanillin as a result of reactions with lignin in wood.
Winemakers usually choose between two types of oak barrels – American (Quercus alba, Quercus bicolor, Quercus macrocarpa) and French (mainly Quercus robur and Quercus sessillis) – and the selection of one of these materials affects the final price of the wine. French oak has a greater capacity to extract solid matter and phenolic compounds, and is also more durable than American oak.