Enzymes as Catalysts

Brewing and baking

Fermentation, which produces ethanol and carbon dioxide, is used in brewing and baking.


The process of fermentation has been used for centuries to produce alcoholic drinks. In this process, enzymes in yeast catalyse the breakdown of sugar molecules in grain or fruit into ethanol. Glucose, for example, is converted by the enzyme zymase into ethanol and carbon dioxide.





2C2H5OH + 2CO2




When does it stop?

The concentration of ethanol resulting from fermentation is limited to about 18%. When this concentration of alcohol is reached the fermentation process stops. To achieve the higher concentration of alcohol that is found in spirits such as whisky and vodka the fermented mixture has to be distilled.


Fermentation is also used to make bread from dough. Brewing and baking are very similar. They both use grain as a starting material and they both rely on fermentation processes involving the enzyme catalysts in yeast. The only difference is that in baking the carbon dioxide is retained in the bread while the ethanol is lost, whereas in brewing it is the alcohol that is retained in the beer while the carbon dioxide is largely lost

It takes about 30 minutes for bread dough to double in volume.