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In most cases, the Clostridium species rank among the sporogenic obligate anaerobes, which are sensitive to bitter hop substances and acidic pH. Thus they rank among the less dangerous contaminants in brewing operations. Their increased incidence in breweries can be linked to the modernization of technologies, which reduces access to oxygen in individual production phases. The endospores of Clostridium bacteria were isolated, e.g., from the storage vessels for liquid malt substitutes (glucose, starch syrups). They are able to survive the conditions of mashing and wort boiling, but they can not germinate in the following phases of beer production. However, their ability to be present in the vegetative form until the wort preparation presents a risk of damage to finished beer – vegetative cells form a number of undesirable organic acids, which may pass into the finished product. We provide here an overview of basic morphological and physiological properties of these bacteria and describe their importance in the brewing process. Particular attention is given to species Clostridium acetobutylicum, C. butyricum, C. cellulovorans, C. pasteurianum, C. thermocellum, „C. thermosaccharolyticum“ (Thermoanaerobacterium thermosaccharolyticum) and C. tyrobutyricum, which were detected in brewing operations.