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The Production of Beer 🍻
In I/GCSE Biology, the anaerobic respiration of yeast breaks sugar down into ethanol and carbon dioxide:
Glucose 🡪 Ethanol + Carbon Dioxide
The ethanol is used in the alcohol for alcoholic drinks such as wine, beer and vodka.
- Barley seeds (which contain starch) are germinated by soaking them in water and laying them out on a flat surface in a malthouse. It produces the enzyme amylase whilst germinating.
- Seeds are killed by heating, without destroying the amylase. This produces a dried product called malt.
- The malt is ground up and mixed with hot water into a mash tun. The amylase breaks down the starch into maltose, producing a sweet liquid. This liquid is boiled to stop the enzymes and is filtered.
- Hops are added for taste and yeast is added to ferment sugars.
- The beer is centrifuged (rotated), filtered and sometimes pasteurised.
- Beer is then put into casks or barrels.
🔎Investigating Carbon Dioxide Production in Yeast
- A small amount of water is gently boiled to drive off any air that is dissolved in the water.
- Sugar and yeast is added to water and stirred.
- A thin layer of paraffin is added to the surface of the mixture to stop oxygen diffusing in from the air.
- The control apparatus is set up, except using killed yeast.
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This experiment can be used to test carbon dioxide production of yeast in other conditions such as different temperatures and concentrations.
The Production of Yoghurt
In I/GCSE Biology, the bacterium used is called Lactobacillus. It produces lactic acid when respiring anaerobically, which turns the liquid milk into yoghurt by coagulating the milk proteins and gives it a slightly sour taste. 👇👇
- Milk is pasteurised at 85-950C for 15-30 minutes, to kill any natural bacteria that it contains.
- It is then homogenised, to disperse the fat globules.
- It is then cooled to 40-450C and inoculated with a starter culture of bacteria. These bacteria digest the milk proteins and ferment lactose into lactic acid.
- The mixture is incubated for several hours. The acid drops the pH of the mixture, coagulating the milk proteins.
- The yoghurt is stirred and cooled to 50C – it slows bacteria growth. Flavourings, colorants and fruit can be added.
That's the end of the topic!
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Drafted by Joey (Biology)