Origin and characterisation of the extractable colour of oak heartwood used for ageing spirits

Abstract

In this study, investigation is focused on the soluble part of oak heartwood colour, with the objective of defining its impact on the colour of spirits after a barrel ageing. Colour is an important parameter for estimating the quality of many beverages and food items. Acetone with 30% water permitted a fast and complete extraction of the soluble colouring matter of heartwood. Water is necessary to improve the extraction of wood fibres by hydration. In heartwood, the repartition of colour is heterogeneous. The outer heartwood, which is new wood, presents a lower soluble colour than the inner heartwood, which is older. This difference is due to the polymerisation by oxidation of the ellagitannins during the natural process of wood ageing and the copolymerisation of cell-wall polymers as polysaccharides.