How is ethanol manufactured from sugarcane ?

Explanation

Molasses is a dark coloured syrupy liquid left the crystallization of sugar from the concentrated sugarcane juice. It contains 30% of Sucrose , which cannot be separated by crystallization.
(i) Dilution of Molasses:
Molasses is first diluted with water to bring down the concentration of sugar to about 8 to 10 percent.
(ii) Addition of Nitrogen Source.
Molasses contains enough nitrogenous matter to act as food for yeast during the fermentation process. If the nitrogenous matter is poor , ammonium sulphate or ammonium phosphae is added.
(iii) Addition of yeast :
This solution kept in large fermentation tank and yeast is added to it kept at about at about 303K for a few days. During the period , the enzymes invertase and Zymase present in yeast, convert sucrose into ethanol.
`underset("Sugar")(C_(12)H_(22)O_(11))+H_2Ooverset("Invertase")rarrunderset("Fructose")(C_6H_(12)O_6)+underset("Glucose")(C_6H_(12)O_6)`
`underset("Fructose(or)Glucose")(C_6H_(12)O_6)overset("Zymase")rarrunderset("Ethanol")(2C_2H_5OH)+2CO_2`
The fermented liquid is technically called wash.
(iv) Distillation of wash
This wash containing 15 to 18% alcohol, is now subject to fractional distillation . The main fraction drawn is an aqueous solution of ethanol which contains 95.5% of ethanol and 4.5% of water. This is called rectified spirit . This mixture is then refluxed over quicklime for about 5 to 6 hour and then allowed to stand for 12 hours.
On distillation of mixture pure alcohol (100%) is obtained This is called absolute alcohol.