The important raw materials containing starch are potatoes, rice, maize, and barley. Of these potatoes are commonly used for the manufacture of ethyl alcohol. The process involves following steps.
Potatoes are cut into slices and crushed. The crushed mass is then steamed at 140-150 temperature degree centigrade under pressure. In this way, the cell walls containing starch particles are broken and starch brought into solution. The resulting solution is called MASH.
- Hydrolysis of Starch to Maltose
The enzyme diastase is needed to hydrolysed starch to maltose. It is present in small amounts in barley and can be developed considerably upon germination. For this purpose, barley is steeped in water at a temperature of 10-13 degree celsius for a couple of days. This is then taken out and allowed to germinate in dark at about 15 degrees C. Barely is then heated to 60-degree celsius to stop germination. The dried and germinated barley is known as MALT.
To the MASH obtained from step ( 1 ) is now added MALT and the temperature are raised to 50-60 degree celsius. Within half an hour diastase present in the MALT converts the starch to maltose.
2( C6 H10 O5 )n + nH2 O Diastase nC12 H22 O11
Starch Maltose
- Fermentation of Maltose to Ethyl Alcohol
Yeast is next added to the Maltose solution. It furnishes the enzymes maltase and zymase, While the former converts maltose into glucose, the latter converts glucose into ethyl alcohol.
- Fractional Distillation of Wash
The fermented liquid or wash obtained above is then subjected to fractional distillation as describe before. The product is 95% ethyl alcohol ( Rectified Spirit ).
Absolute Alcohol. Absolute ethyl alcohol is 100% pure ethyl alcohol. Commercial alcohol ( Rectified Spirit ) is a mixture of 95% ethyl alcohol and 5% water. This mixture can not be separated by further distillation. Such a solution is called Azeotropic Mixture or Azeotrope.
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