Abstract: Brewing process including mashing, boiling, fermentation and filtration was studied by electron spin resonance(ESR) method in this paper. It was found that free radicals were yielded mostly during boiling phase, while a decline after fermentation and an increase after filtration occurred. Free radical generation courses of each phase before or after fermentation were different, especially between wort and beer, which meant different kinds of oxidants in them. The former has a persistent effect mainly inhibiting the antioxidant formation in late incubation, while the latter has a rapid effect of scavenging the antioxidant in the early incubation. A new-type free radical (FR1) is found in the saccharifying phase related intimately to the formation and quantity of ·OH.

Key words: free radical, ESR(electron spin resonance), beer, brewing, mashing