Learning outcomes:
understand the role of yeast in the production of beer
describe a simple experiment to investigate carbon dioxide production by yeast, in different conditions
understand the role of bacteria (Lactobacillus) in the production of yoghurt
interpret and label a diagram of an industrial fermenter and explain the need to provide suitable conditions in the fermenter, including aseptic precautions, nutrients, optimum temperature and pH, oxygenation and agitation, for the growth of micro-organisms

Remember that yeast are capable of respiring aerobically (producing CO2 and water) and anaerobically (producing CO2 and ethanol). Yeast are therefore used in the brewing industry.
In order to make beer barley seeds are allowed to germinate by soaking the barley seeds in warm water. This is called malting. The germinating barley seeds break down their carbohydrate stores, releasing sugar. After a couple of days the barley seeds are gently roasted (which kills them) and put into a fermenter with yeast. The yeast use the sugar for anaerobic respiration and produce beer.
You need to know an experiment that shows the production of CO2 by yeast, in different conditions. The best example is to mix a yeast suspension with a sucrose solution and place in a boiling tube with a delivery tube attached. Any CO2 produced can be collected over water or bubbled through lime water.


Lactobacillus bacterium is This bacterium is used to turn milk into yoghurt. It uses lactose sugar in the milk to produce lactic acid by anaerobic respiration. The lactic acid affects the milk proteins, making the yoghurt curdle (go solid) and giving it the characteristic tart taste.


Important details:

Cooling jacket – keeps the microorganisms at optimum temperature. They will produce lots of heat through respiration, therefore need to be cooled!
Paddles – keep stirring the mixture. This stops waste products from building up and keeps the air evenly mixed
Nutrient medium – supplies the microorganisms with fuel for respiration
Sterile air supply – supplies clean O2 for respiration (note: this is not required in anaerobic fermentation processes)
Data-logger – monitors temperature and pH, keeps the fermenter at optimum conditions

You don’t need to be able to draw this out, but you could be asked to label a diagram of a fermenter or be asked to explain the function of the various parts of a fermenter.