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French oak (''Quercus sessilis'' and ''Quercus robur'')-----. French oak contributes comparatively more [https://en.wikipedia.org/wiki/Trans-3-Methyl-4-octanolide trans-lactones 3-Methyl-4-octanolide] while American oak contributes more [https://en.wikipedia.org/wiki/Cis-3-Methyl-4-octanolide cis-lactones 3-Methyl-4-octanolide] to beer. The total lactone contribution is higher in American oak. ''Q. sessilis'' is more common in wine aging and ''Q. robur'' is more common for cognac barrels <ref name='Review of oak aging for wine'>[http://www.sciencedirect.com/science/article/pii/S092422440600015X Review of quality factors on wine ageing in oak barrels. GargeGarde-Cerdan and Ancin-Azpilicueta (2006)]</ref>. These lactones both contribute a coconut character but the cis-lactone has a much lower flavor and aroma threshold <ref>[http://www.sciencedirect.com/science/article/pii/S0023643805000150 Effect of oak barrel type on the volatile composition of wine: Storage time optimization. Garde-Cerdan and Ancin-Azpilicueta (2006)]</ref>, therefore American oak barrels may give more of a lactone flavor and aroma impact. ''Q. sessilis'' is more common in wine aging and ''Q. robur'' is more common for cognac barrels <ref name='Review of oak aging for wine'/>