Zymomonas is a waterborne unwanted bacteria in beer, creating an estery-sulfury flavour due to the production of acetaldehyde and hydrogen sulfide. This can be likened to a rotten apple smell or fruity odor. Zymomonas haven't been reported in lager breweries due to the low temperatures (8 to 12 degrees Celsius) and stringent carbohydrate requirements (able to ferment only sucrose, glucose, and fructose). It is commonly found in cask-conditioned ales where priming sugar is used to carbonate the beer. The optimum growth temperature is 25 to 30 degrees Celsius.