Loz Metal Head:
Sugar cane can be used to produce ethanol commercially in large amounts.
The first stage in ethanol production from sugar cane is milling. The grains from the sugar cane are passed through hammer mills. These hammer mills grind them into a fine powder. This fine powder is now called meal.
The meal is then sent to the mashing system. At the mashing system, the meal is mixed together with enzymes and water.
This mixture is then passed through cookers which heat up the mixture. This heat effect turns the starch into its liquid form. The enzymes start breaking down the sugar cane to pure to sugars. This mash from the “cookers” is cooled and then allowed to enter the fermentation stage
The yeast is added to the mash, which converts the sugars into ethanol and carbon dioxide as it acts as a biological catalyst. The carbon dioxide can be removed as the industry is only interested in keeping the ethanol as its end product.
Enzymes produced by yeast, such as invertase, are necessary for the fermentation processes to occur. Sugar cane is broken down into glucose and fructose:
(invertase)
C12H22O11 + H2O C6H12O6 +C6H12O6
(cane sugar) (water) (glucose) (fructose)
The glucose is then further fermented to produce ethanol:
(zymase)
C6H12O6 2C2H5OH + 2CO2
During the fermentation process, nutrients such as phosphoric acid and urea are allowed into the fermenters to ensure that the yeast continues growing. The maximum concentration of ethanol that can be produced is 15%. At concentrations higher than this, the ethanol will start to kill the yeast and the production of ethanol will stop.
The mixture is then continually pumped into a distillation system where the ethanol is removed from the mixture and then the mixture can be left to ferment again.
The alcohol that is removed during distillation is approximately 96-97% pure. This is then
dehydrated to remove the last impurities and water molecules. After this process, the ethanol can then be sold commercially as it is anhydrous."
This is from the link posted in this thread.
While Moiselles notes are highly summarised and really good I think Loz's response is probably what youre looking for the dot point.