Fermented malt beverages with reinforced filling taste and fullness of mouthfeel are manufactured by addition of .alpha.-glucosidase prior to a heat treatment in a wort production process in the course of manufacturing fermented malt beveragesProduction of acetic acid can be reduced by addition of .alpha.-glucosidase in the fermentation process in the high gravity brewing of beer. Further, low-calorie beers are manufactured by the method in which .alpha.-glucosidase is added in the fermentation process in brewing of beer and thereby real fermentation degree is enhanced.