Saturday, 1 December 2012


Saccharomyces cerevisae is the species of yeast used for bread making. It is often known as baker's yeast. But if you look carefully at its name you will notice that this species is not only used in bread making but also in the making of beer (cerveza in spanish). The making of both of these products is based on a chemical reaction carried out by these unicellular living things, called fermentation. Fermentation is the process by which yeast cells metabolize the sugar in wheat, in the case of bread or malted barley in the case of beer to obtain energy. Fermentation is usually occurs in the absence of oxygen and is known as an anerobic reaction. In the presence of oxygen cells obtain energy through respiration which is known as a aerobic reaction. Although some species of yeast tend to prefer fermentation. In this process carbon dioxide and alcohol (ethanol) are formed. The carbon dioxide is a gas and forms bubbles of air in the bread making it rise. The alcohol is evaporated by the heat of the oven in the case of bread.

                      C6H12O6 → 2C2H5OH + 2 CO2
                           a molecule of glucose is converted into 2 molecules of ethanol and 2 of carbon dioxide

This simple experiment shows how gas is released during fermentation. After some time the balloon fills with carbon dioxide. The water must be warm and sugar must be added. This is exactly what happens during bread and beer making.
Erlenmeyer flask with a balloon attached
After some time the balloon fills with carbon dioxide released during fermentation carried out by this one celled fungus.
You can smell a scent of alcohol too when you pull the balloon off.

Check out these two Discovery Channel videos on bread and beer making! 

Click here:      Bread Making!
Click here:   Beer making!

1 comment:

Miguel Prats said...

This is very interesting