The 'Gazette'
Ageing in oak is an essential stage in the crafting of a whisky. At the heart of this ageing process is an often overlooked but essential player: oak. This majestic tree is the main material used for casks. It plays a fundamental role in developing the flavours and aromas of whisky. Let’s delve into the fascinating world of oak and discover how its unique properties influence whisky maturation.
Oak is much more than just a container for whisky ageing. Its remarkable mechanical properties, natural heat insulation and watertightness make it the preferred choice for cooperages. Three species dominate within the craft: Quercus petraea, Quercus robur and Quercus alba. These varieties of oak, thanks to their specific composition and growing conditions (geography, climate), give whisky its distinctive sensory characteristics.
Anatomy of oak wood
Oak wood is made up of several layers, each playing an essential role in the creation of high quality casks:
– The suber (bark): impermeable, it allows the gas exchanges that are essential to the respiration of the internal cells.
– The phloem: responsible for transporting sap, it nourishes the growing cells.
– The cambium: this thin layer of living cells is where the wood grows in thickness.
– Sapwood (imperfect wood): the young, supple part of the tree, it transports the raw sap.
– Duramen (perfect wood): this is the heart of the cask, rich in lignin and tannins, essential for whisky ageing.
– The heart (pith): the centre of the tree, symbolising the start of its growth.
– The medullary rays: these store nutrient reserves, essential to the tree’s health.
Oak growth is marked by two types of annual rings. A distinction is made between spring wood, which is more porous and lighter, and summer wood, which is denser and more compact. These variations, influenced by the environment, climate and genetics, determine the structure of the wood grain.
One of the most important characteristics of wood used in cooperage is its grain. Grain is defined by the average width and regularity of the annual growth rings:
– Fine grain: resulting from slow growth (2 mm/year), this homogeneous grain encourages controlled oxygenation of the whisky.
– Medium grain: resulting from moderate growth (4 mm/year), it offers a balance between porosity and density.
– Coarse grain: born from rapid growth (6 mm/year), its heterogeneous structure influences ageing.
Relationship between oak wood structure and grain size
By mastering the unique and singular properties of oak, we perfect ageing, offering creations of remarkable finesse. In another article, we’ll look at the importance of natural drying, a crucial stage in revealing the full aromatic potential of the barrels.
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Vivas, N., Debeda, H., Menil, F., Vivas de Gaulejac, N., &Nonier, M.F. (2003). Mise en evidence du passage de l’oxygène au travers des douelles constituant les barriques par l’utilisation d’un dispositif original de mesure de la porosité du bois. Premiers résultats. Sciences des Aliments,23, 655-678
Doussot, F., De Jéso, B., Quideau, S., & Pardon, P. (2002). Extractives content in cooperage oak wood during natural seasoning and toasting; influence of tree species, geographic location, and single-tree effects. Journal of Agricultural and food chemistry, 50(21), 5955-5961
Maturation | October 2024 | Dr. Magali Picard