AIST conducted joint research with the Research Laboratories for Alcoholic Beverage Technologies, R&D Division of Kirin Co., Ltd., using sum-frequency generation spectroscopy (SFG spectroscopy) effective for surface analysis to directly measure the surface of beer and clarify the behaviors of hop-derived molecules on the surface and proteins contained in beer.

Conceptual illustration of hop-derived molecules and proteins contained in the gas-liquid interface of beer foam

It was already known that beer foam contains proteins and ingredients from hops that give beer its bitter taste. Major bitter ingredients are isohumulones that also affect the formation of beer foam. However, it was unclear whether they existed in the liquid part of the foam or at the interface between gas and liquid (the gas-liquid interface).

The researchers investigated the surface of beer using SFG spectroscopy, which can selectively measure the vibrational spectra of molecules present on the surface and interface of solids and liquids. They found that there are both hop-derived molecules containing the source of the bitter flavor of beer, as well as proteins on the surface of beer. They also found that there is a correlation between the amount of hop-derived molecules on the surface and the stability of beer foam. Adding more hops during the beer brewing process improves the stability of foam (duration of the foam).

In the future, the researchers will use surface and interface measurement and analysis techniques used this time to clarify the molecular behavior of gas-liquid interfaces and characteristics of various materials.