I/GCSE Biology - The Production of Beer and Yoghurt

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.

1.  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.
2. Seeds are killed by heating, without destroying the amylase. This produces a dried product called malt.
3. 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.
4. Hops are added for taste and yeast is added to ferment sugars.
5. The beer is centrifuged (rotated), filtered and sometimes pasteurised.
6. Beer is then put into casks or barrels.

1. A small amount of water is gently boiled to drive off any air that is dissolved in the water.
2. Sugar and yeast is added to water and stirred.
3. A thin layer of paraffin is added to the surface of the mixture to stop oxygen diffusing in from the air.
4. The control apparatus is set up, except using killed yeast.

This experiment can be used to test carbon dioxide production of yeast in other conditions such as different temperatures and concentrations.

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. 👇👇

1. Milk is pasteurised at 85-95⁰C for 15-30 minutes, to kill any natural bacteria that it contains.
2. It is then homogenised, to disperse the fat globules.
3. 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.
4. The mixture is incubated for several hours. The acid drops the pH of the mixture, coagulating the milk proteins.
5. 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!

CLICK HERE TO LEARN MORE ABOUT OUR I/GCSE BIOLOGY COURSES

Drafted by Joey (Biology)