1. National Biology
Properties of micro-organisms and their use in industry
a: Yoghurt and Cheese

2. Recap
Think about:
The different types of cells we have come across so far
Any processes that you are aware of that involve the use of micro-organisms in day-to-day life

3. What are we learning today?
We are learning to:
State what type of micro-organism is used in the manufacture of cheese and yoghurt
Explain the processes involved in the manufacture of cheese and yoghurt
Success criteria:
Explain lactic acid fermentation by bacteria

4. What type of micro-organism is used to make cheese and yoghurt?
Bacteria are used to make cheese and yoghurt

5. Cheese Making Cheese is also made from milk
There are several steps involved in cheese making
Bacteria is added to the milk to thicken it
Rennet (an enzyme) is added to clot the protein in the milk
The solid curds are separated from the liquid whey
The curds are moulded into cheese blocks
Jimmy's farm: making cheese

6. Cheese Making Jimmy's farm: making cheese Experiment
Collect three test tubes/boiling tubes
Pour in 5mls of milk
Add rennet to each tube
Leave to stand for 20mins
Observe results
Write report of experiment in jotter

8. Bacteria in yoghurt The Nigrosin Stain Technique
Follow your instructions carefully
You may see rods or cocci or both on your slide

9. How is yoghurt made? Yoghurt is made by the souring of milk
Yoghurt forming bacteria are added to the milk
The bacteria carry out lactic acid fermentation
lactose sugar lactic acid
The lactic acid thickens the milk and gives it the sour flavour
The pH of the yoghurt drops and acts as a natural preservative

10. Yoghurt making Jimmy's Farm: making yoghurt
You will now make yoghurt in the lab using bio yoghurt as a starter culture (contains bacteria already)

11. The yoghurt making process
The milk should be warm to provide good growing conditions for the bacteria
Once the starter culture has been added to the milk the mixture is kept warm for at least 7 hours to allow the bacteria time to multiply and act on the lactose
After the milk has been converted to yoghurt it is put in the fridge to prevent the bacteria continuing to sour the milk which would make it inedible

12. Cheese and yoghurt Quiz
What is used to make yoghurt?
What do the bacteria do to the yoghurt?
What is the lactose in the milk converted into and what effect does this have on the yoghurt?
Why is rennet added to thickened milk during cheese making?
What are the solid and liquid parts of cheese making?