Factors affecting 5-hydroxymethyl furfural formation and stale flavor formation in beer

5-Hydroxymethyl furfural (5-HMF) and furfural are index compounds for beer staling. A correlation exists between the organoleptically determined degree of staling flavor in beer and 5-HMF levels during storage. This suggests that controlling 5-HMF formation during brewing might provide useful clues for improving the flavor stability of beer. Various experiments performed to control the levels of 5-HMF show that active oxygen and low pH in a finished beer enhance the formation of 5-HMF during storage. Using antioxidative mashing and selecting yeast strains with higher cellular volume are effective, practical methods for regulating these levels. Cell sizes of yeast strains (calculated from photographic images of about 100 cells) were found to correlate with the beer pH levels produced by those strains. Using pitching yeast with a larger cell size resulted in a higher pH level of beer and a lower level of 5-HME.