Beer Foam is a Carrier of Aroma

A headspace-proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF/MS) system that combines PTR-TOF/MS with a dynamic and reactive flavor-release monitoring system was constructed to measure the orthonasal aroma components in beer before and after foaming. Some aroma components in the headspace of beer after foaming in real time, such as m/z 145.1150 and m/z 173.1536, are thought to be derived mainly from ethyl hexanoate and ethyl octanoate, respectively, resulting in a fruity and sweet aroma. They showed significantly higher volatilizations than those in the headspace before foaming. The ratio of the concentration of headspace m/z of beer after foaming and before foaming showed a significant correlation with the partition coefficient of each assuming the main aroma component, indicating that the volatility of beer aroma with foaming depends on the hydrophobicity. The aroma components with high partition coefficients were believed to be able to associate with isohumulones and some proteins and to move to foam during foaming. They might be more volatilized by collapsing bubbles than those with low partition coefficients. Beer foam plays a novel role as a carrier of aroma, specifically promoting the release of some characteristic aroma compounds.