Oak Flavour: Lactones

These compounds, responsible for what is generally called the aroma of oak, or ‘oakiness’, are derived from lipids in the oak. There may be variances in lactone levels in different trees and even in different parts of the same tree. Lactones are more coconut-like at higher concentrations and can easily overpower a wine’s inherent aroma. Higher concentrations are found in American oak although studies by French cooper Taransaud have shown that during air drying of the staves prior to barrel making, some lactones increase while others decrease, and lactone levels decrease in American oak and increase in French. Toasting of the oak may increase the flavour. The specific compounds are the cis and trans isomers of ρ-methyl-g-octalactone. The former is more aromatic and imparts an earthy, herbaceous character; the latter imparts more spiciness and has a higher threshold value in wine. Seasoning affects the ratio of cis to trans isomers.