Decrease in hydrogen sulfide content during the final stage of beer fermentation due to involvement of yeast and not carbon dioxide gas purging

We observed a rapid decrease in hydrogen sulfide content in the final stage of beer fermentation that was attributed to yeast and not to the purging of carbon dioxide (CO2) gas. The well known immature off-flavor in beer due to hydrogen sulfide (H2S) behavior during beer fermentation was closely investigated. The H2S decrease occurred during the final stage of fermentation when the CO2-evolution rate was extremely small and there was a decrease in the availability of fermentable sugars, suggesting that the exhaustion of fermentable sugars triggered the decrease in H2S. An H2S-balance analysis suggested that the H2S decrease might have been caused due to sulfide uptake by yeast. Further investigation showed that the time necessary for H2S to decrease below the sensory threshold was related to the number of suspended yeast cells. This supported the hypothesis that yeast cells contributed to the rapid decrease in H2S during the final stage of beer fermentation.