Why raise a wine in oak barrels?

The aging in oak or barrel is at the origin of the invention of wine as we know it today. As explained in our story of the barrel, the Roman wine raised in amphora was so different from ours that nobody would deign to drink it today. But let us see in detail what are the practical reasons for raising wine in oak barrels.

Wine aging in oak barrels: the logistical reasons

Certainly, the wine could be raised in oak barrels for logistical reasons: the amphora barrel replaced in just a few centuries was breakable, not easy to stack and handle. The wooden barrel, both round and solid, was instead a vessel easy to move and store: you could roll the barrel and then stack it on wagons or boats, without the risk of breaking at the slightest hitch .

The oenological reasons for the wine aging in oak barrels

The oak barrel nevertheless has a primary oenological role: the passage of the amphora to the barrel has modified the nature of the wine, allowing a natural vinification. The aging of a wine in oak barrels makes it possible to dispense with spices and other exotic products: the winemaker can rely on the resources of his soil.

On a technical level, the aging of a wine in oak barrels allows a series of reactions that one would not have with a tank made of stainless steel, resin or concrete.

Here are the specific contributions of oak barrel aging:

Micro-oxygenation of the wine through the oak: exchanges are made between the outside and the inside of the barrel. Oxygen slips into the pores of the wood, but also between the staves and the hole in the bung. The importance of each of these factors varies according to the age of the barrel and the type of filling, depending on whether the plug is just seated or hammered into the side of the barrel. These processes contribute directly to the maturation of the wine and the modification of the tannin structure. For more information, see our fact sheet dedicated to the role of micro-oxygenation.

Dissolution of extractable constituents of wood conferring an aromatic complexity, a better aptitude for aging and more sustained colors. These last compounds are numerous and one will quote the most important classes:

Volatile phenols such as eugenol (clove, carnation) or guaiacol (smoked, toast): their content increases and works during the maturation of staves and bousinage.

Β-methyl-γ-octalactones also known as "whiskey lactones" or "oak lactones": they are present in the form of two cis and trans isomers; their molecule is identical in its composition, but certain dispositions of atoms and functional groups differ. Concretely, this slight variation in the molecular configuration confers neighboring properties: the two isomers give off a smell of coconut and fresh wood. But the cis form is more fragrant and powerful, with lower perception thresholds. Its high presence in American oak (white oak such as Quercus Alba) gives very woody tastes and explains why our cooperage prefers French wood, with a particular preference for Quercus Robur, pedunculate oak. This one presents reasonable contents of whiskey-lactones which allow to raise wines in oak barrel without crushing them under the "woody". To be clear, it is not so much undergrowth that may give a taste "too woody", that β-methyl-γ-octalactones in their cis form, especially if we use American oak for the sake of economy (the presence of many thick thylons in his vessels allows to make staves by sawing rather than splitting, which is more profitable

The ellagitannins: these are the oak tannins. The three most important are castalagine, vescalagin and roburines. The natural drying of stave wood reduces their content, but in the case of aging in new casks, a significant amount passes into the wine during the first months of aging. These hydrolysable tannins solubilize and cause what is called the "catch of wood": their pronounced taste disappears quickly because they are very oxidizable: after 4 to 6 months, their woody contribution fades and ends up to degrade with time. This sensitivity plays a direct role in the evolution of wine aged in oak barrels: with the ellagitannins, the redox potential increases even without oxygen. They thus allow a free radical uptake which protects from a too brutal oxidation, while degrading the nauseating thiols which are the source of the bad tastes of reduction. This oxidation-reduction potential is finally expressed in the color that ellagitannins contribute to stabilize.

In addition to all this, non-volatile wood compounds dissolve in the wine. Without claiming to be exhaustive, there may be mentioned coumarins, polysaccharides derived from hemicellulose, lignins, etc. The contributions and their effects combined with wine are so numerous and complex that science still has something to do ...