National Biology
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Transcript of National Biology
National BiologyProperties of micro-organisms and their use in
industrya: Yoghurt and Cheese
RecapThink about:The different types of cells we have come
across so farAny processes that you are aware of that
involve the use of micro-organisms in day-to-day life
What are we learning today?
We are learning to:State what type of micro-organism is used in
the manufacture of cheese and yoghurtExplain the processes involved in the
manufacture of cheese and yoghurt
Success criteria:Explain lactic acid fermentation by bacteria
What type of micro-organism is used to make cheese and yoghurt?
Bacteria are used to make cheese and yoghurt
Cheese Making• Cheese is also made from milk• There are several steps involved in cheese
making1. Bacteria is added to the milk to thicken it2. Rennet (an enzyme) is added to clot the
protein in the milk3. The solid curds are separated from the liquid
whey 4. The curds are moulded into cheese blocks
Jimmy's farm: making cheese
Cheese MakingJimmy's farm: making cheeseExperimentCollect three test tubes/boiling tubesPour in 5mls of milkAdd rennet to each tubeLeave to stand for 20minsObserve resultsWrite report of experiment in jotter
Bacteria in yoghurtThe Nigrosin Stain TechniqueFollow your instructions carefully
You may see rods or cocci or both on your slide
How is yoghurt made?Yoghurt is made by the souring of milkYoghurt forming bacteria are added to the milkThe 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
Yoghurt makingJimmy's Farm: making yoghurt
You will now make yoghurt in the lab using bio yoghurt as a starter culture (contains bacteria already)
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
Cheese and yoghurt Quiz1. What is used to make yoghurt?2. What do the bacteria do to the yoghurt?3. What is the lactose in the milk converted
into and what effect does this have on the yoghurt?
4. Why is rennet added to thickened milk during cheese making?
5. What are the solid and liquid parts of cheese making?