The properties of a new bacterial genus that is capable of growth in hopped beer are described. The organism is an anaerobic gram-negative, non-spore forming mesophilic rod with flagella emanating from one side of the cell body. It produces a considerable amount of H2S and high turbidity when grown in packaged beer. No alcohol was produced from glucose unlike the genus Zymomonas. The guanine-plus-cytosine content of the deoxyribonucleic acid is 39*8 mol %. The physical and biochemical characteristics of this organism indicate that it is not related to any of the brewing bacteria so far reported in the literature including the genus Zymomonas. We have proposed the new genus and species Pectinatus cerevisiiphilus in the family Bacteroidaceae*. The type strain has been deposited in the American Type Culture Collection (ATCC) under the number 29359.