Assessing the Feasibility of Using Small Pieces of Mizunara Oak as Inner Staves within Ex-Bourbon Casks for Whisky Maturation: An Opportunity for Sustainable Bioresource Management?

Mizunara oak, a rare and costly Japanese oak, poses challenges for whisky cask production due to limited availability. The coopering process of Mizunara oak casks often produces small pieces of wood unsuitable for cask-making. This study investigates the use of the small pieces as inner staves within ex-Bourbon casks to economically and sustainably produce Mizunara oak-matured whiskies. A 12-week accelerated maturation experiment was conducted with four sets of lab-scale vessels, using Mizunara and American oak cubes as inner staves. Two sets of bell jar vessels mimicked commercial casks with either Mizunara or American oak inner staves, while two mason jar sets compared the effects of Mizunara oak alone with the combined Mizunara and American oak. Accelerated maturation was achieved with a surface area to volume ratio of 260 cm2/L, 2.7 times higher than in typical 200 L casks. Samples were analysed every 4 wk for alcohol content, colour and flavour development. In the bell jars, Mizunara oak impacted maturation with higher concentrations of key congeners. Sensory analysis revealed distinct differences between spirits matured with Mizunara versus American oak. In the mason jars, minimal differences were observed between Mizunara-only and combined oak samples. The study suggests Mizunara oak inner staves have a notable effect on whisky maturation, whether used alone or combined with American oak. Using such small pieces as inner staves appears to be a promising method for producing Mizunara oak-derived flavour in whiskies. This approach promotes sustainable bioresource management by utilizing cooperage by-products, potentially applicable to other valuable wood species.