Production of Ethanol by

Fermenting Sugars

ETHANOL

One method of making ethanol is to use plant material which contains starch.

The reaction is called fermentation where the sugar is converted into an alcohol.

Fermentation is an enzyme-controlledreaction that takes place inside living yeastcells in which glucose is broken down intoalcohol and carbon dioxide with the releaseof energy.

The carbohydrates in the food must be broken

up first to form sugars. This is done by hydrolysing the carbohydrate.

Hydrolysis is a reaction in which watermolecules (‘hydro’=water) react with largermolecules to split them (‘lysis’= split apart)into two or more smaller molecules.

part of a starch molecule

individual glucose molecules

H

H

O

H

H

O

H

H

O

water molecules

The sugar is then converted into alcohol.

The equation for the reaction is :

glucose → ethanol + carbon dioxide

C6H12O6 → 2C2H5OH + 2CO2

Fermentation is an enzyme-controlled reaction that takes place inside living yeast cells in which glucose is broken down into alcohol and carbon dioxide with the release of energy.

Reactions that are catalysed by enzymesnormally produce the best results at temperatures around 40OC.

The reactions will be slower at lowertemperatures and at higher temperatures,

over 70OC, the enzyme will stop working because the high temperature denatures the enzyme.

The fermentation process takes place insideliving cells therefore if the yeast dies thenthe reaction will stop.

When the alcohol concentration reaches about

14% the it begins to kill the yeast.

Fermentation reactions therefore have alimit to the percentage of alcohol they canproduce.

Biological Action

Yeast:

• Living organism• Microscopic fungus• Feeds on sugars• Is a biological catalyst• Therefore classed as an enzyme

Conditions for Fermentation

pH: prefer a neutral pH (or round about) if it is too acidic or alkaline the yeast will die.

Temperature: Room temperature is ideal; too cold and the yeast stops

working (goes into a “sleep” state) and too warm and it dies.

Alcohol concentration: yeast does not like alcohol, about 14% alcohol the yeast

dies

Distilling The Alcohol

The alcohol concentration can be increased by

separating the alcohol from the water, this is carried out via a process called distillation.

The separation by distillation is an easy process as ethanol boils at 78OC and waterboils at 100OC although both liquids will evaporate to some extent at any

temperature.