Direct detection of beer photodegradation in commercial bottles and introduction of a new Light-Struck Flavour Susceptibility Index

has a specific, so-called skunky or light-struck flavour (LSF). The compound responsible for LSF is 3-methylbut-2-
ene-1-thiol (MBT). Riboflavin (RF) plays a key role in the formation of MBT. It absorbs light in the blue part of the
spectrum and transfers excitation energy to isohumulones. This process is accompanied by the decomposition of RF,
which causes a decrease in the absorbance of the sample at 450 nm. The decomposition is directly related to the
formation of LSF. In this study, the decrease in absorbance associated with the defined illumination of model and real
beer directly in commercial bottles was measured. The decrease in absorbance correlated with the decrease in RF
concentration and the formation of LSF detected by the sensory panel. The Light-Struck Flavour Susceptibility Index
was introduced as a rate of the beer susceptibility to light degradation and the formation of LSF.