The 'Gazette'
Toasting is a combination of two vital steps in the barrel manufacturing process. As we have seen previously ( Master Notes #3), the first step is combining heat with steam to make the wood polymers more flexible, facilitating the stave bending. The second step consists of heating the inside of the barrel, called aromatic toasting, or “bousinage”.
Whilst stave bending is only a mechanical process, toasting provides a significant organoleptic benefit to the whiskies. Through the thermal degradation of wood polymers, the wood’s molecular composition is modified, leading to the generation and release of new aromatic compounds.
Several types of toasting are used by cooperages. They are determined according to the height and intensity of the flame, the toasting duration and the quantity of water vaporised on the outside of the barrel. The result is a specific chemical profile for each type of toasting, that will therefore influence the organoleptic properties of the aged whiskies.
Between ambient temperature and 140°C, the wood loses nearly no water.
Between 140 and 250°C, the wood turns brown, loses water and carbon dioxide.
Above 250-260°C, there is an exothermic reaction, resulting in carbonisation: the formation of charcoal.
The sensory complexity of a great whisky is largely determined by the molecules it extracts from the oak wood as it ages. There are many such molecules, formed at different stages during the toasting process. In the next article, we’ll look at the aromatic compounds produced during this specific heating process.
Vivas, N., Bourgeois, G., Saint-Cricq de Gaulejac, N. & Glories, Y. (1997). Arômes et Précurseurs d’arômes du bois de chêne en tonnellerie. Analusis, 6(25), 19-23
Puech, Y. & Maga, J. (1993). Influence du brûlage du fût sur la composition des substances volatiles et non volatiles d’une eau-de-vie d’Armagnac. Revue des OEnologues, n°70, page 13- 16
Maturation | December 2024 | Dr. Magali Picard