This report studied the production of SO2 by brewer's yeast during beer fermentation,and follow-up detection of the change of SO2.The results showed that SO2 generated in the fermentation process mainly came from the sulfate in the wort absorbed and reduced by yeast when it synthesized methionine.The formation of sulfur dioxide by yeast metabolic can be regulated by various kinds of amino acids,especially methionine.During the fermentation the formation of SO2 increased at the beginning,then slowly declined,and finally reached the stable status.