WINETECH Technical Yearbook 2021

PRACTICAL IN THE CELLAR | APRIL 2021

Bitter compounds in oak wood CHARL THERON: Private consultant KEYWORDS: Bitterness, oak wood.

THE MATURATION OF WINE in oak barrels has an influence on the colour, flavour and taste of wine. Although the aim of wood maturation is the improvement of wine, it can also have detrimental effects. Bitterness is one of these. Coumarin is a bitter compound, which occurs in oak wood and can transfer the bitterness into the wine if it is matured in oak. Individually the concentration of the compounds is too low to be observed, but together their concentration is high enough to be observed. It is well-known that tannins can cause bitterness, but cooperages must also attend to the influence of coumarin compounds. Coumarins also occur in medicine for blood clots, cancer tumours and gallstones. Coumarin is a chemical compound, which is formulated as C 9 H 6 O 2 . It occurs especially in sweet smelling plants to protect them against pathogens. Coumarin smells sweet, but tastes bitter.

Apart from coumarin as such, derivatives thereof, namely esculetin, umbelliferone, scopoletin, 4-methylumbelliferone and fraxetin, also occur in different plants. All six compounds were identified in commercial wine and spirits samples, but they occur in higher concentrations in red wine. Although the compounds smell sweet, they do not contribute to the sweet taste of matured spirits or wine. Research regarding the compounds is supported by cooperages like Sequin Moreau and Demptos. The natural drying of wood, before the assembly of barrels is a key factor in the coumarin concentration of wood-matured spirits and wine. The air drying of wood is not only a drying process, but also a maturation process. It is caused by the growing of certain micro-organisms, forming extracellular enzymes. These enzymes contribute to the hydrolysis of coumarin compounds.

Wood toasting has an influence on the bitterness of wood.

WINETECH TECHNICAL YEARBOOK 2021 | 154