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National Biology

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

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National Biology

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  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

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

  8. 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

  9. 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)

  10. 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

  11. 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?

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