1. Micro- organisms and food How bacteria and yeast are used to produce foods and other products such as medicines

2. Making yoghurt  Milk is pasteurised to sterilise it  It is homogenised to mix in the fat  Cooled and inoculated with bacteria  Incubated at 40-45 degrees to digest bacteria and ferment lactose  Stirred and cooled so it sets  Other ingredients may be added now

3. Making beer  Barley seeds are germinated and make amylase  They are killed and dried to make malt  Malt is ground and mixed with water; amylase turns starch to maltose  Mash is boiled and filtered  Hops are added, and yeast for fermentation  Beer is centrifuged and sometimes pasteurized

4. An industrial fermenter  Glucose & amino acids are added (substrate)  Suitable organisms are added  Sterilised (filtered) air is pumped in  The mixture is agitated (stirred) using paddles  The waste gas outlet removes CO 2  It is all computer-controlled: pH, temperature, CO 2 and O 2 are monitored using a data logger  The product is removed and filtered to extract the desired substance (e.g. insulin or penicillin)