Fermentation is used commercially on a large scale in
various countries to produce ethanol from sugar crops
(e.g. sugar cane,sugar beet) and starch crops (e.g. maize,
wheat). The biomass is ground down and the starch
converted by enzymes to sugars,with yeast then converting
the sugars to ethanol. Purification of ethanol by
distillation is an energy-intensive step,with about 450 l
of ethanol being produced per ton of dry corn. The solid
residue from the fermentation process can be used as
cattle-feed and in the case of sugar cane,the bagasse can
be used as a fuel for boilers or for subsequent gasification