Ethanol is obtained by fermentation of glucose (which is often obtained from starch) in the presence of yeast.  Carbon dioxide is cogenerated. Like ethanol, butanol can be produced by fermentation processes. Saccharomyces yeast are known to produce these higher alcohols at temperatures above . The bacterium Clostridium acetobutylicum can feed on cellulose (also an alcohol) to produce butanol on an industrial scale.