The use of oak barrels commenced 2000 + years ago in Roman times as the preferred method of storage and transport for wine. Over time, winemakers discovered that wine stored in oak barrels gave it softer and better tasting properties.
Wines can either be directly fermented in oak barrels (both primary and malolactic) and / or used for maturation after fermentation.
The maturation and softening of red wines requires a small controlled quantity of oxidation. The porous nature of an oak barrel allows both a tiny ingress of air as well as some evaporation of water and alcohol which concentrates the wine’s flavour. The wood also imparts some of its flavour to the wine giving it a touch of sweetness, vanilla and spicy / smoky aromas. A winemaker will select different barrels (age and wood) for different grape varieties and vineyards according to the final taste required.
Losses from the barrel during maturation are replenished by topping up with vat or press wine – inaccurate pouring, sampling and expansion (when ful)l explain the strong red colours on the central band of the barrel. Barrels are tapped with a rubber hammer to release trapped bubbles of air in the barrel prior to resealing.
The most common barrel size is 225 litres (59 US gallons) and is called a “Barrique”. Oak wood is sourced most commonly from French American, Hungarian or Rumanian forests.