Wednesday, February 15, 2012

OBJ 5.5 Beer Production

Understand the role of yeast in beer production 

Beer is an alcoholic drink made by fermentation reaction that uses yeast to convert sugars to ethanol.
Fermentation also means "anaerobic respiration."

1. Sugar from plant material (barley) is converted into ethanol and carbon dioxide by fermentation. Yeast is used as a natural catalyst.

Sugar --> ethanol + carbon dioxide

C6H1206 ---> (enzymes in yeast) --> 2CH5OH +2CO2

2. The starch in barley is first broken down into sugar so that the yeast cells can ferment it to ethanol.

3. When barley seeds germinate (process is called "malting", they produce the enzyme amylase which breaks down starch into maltose - this is used by the yeast as an energy source in fermentation.

4. Sugars for beer-making come from boiling the barley in water - Hops are then added to adjust the flavor of beer making it bitter, and stop bacteria growing. 

The yeast is then added and after a while it uses up all the oxygen in the mixture and startes to respire the sugars anaerobically.

5. Flow of stages in beer production

Barley seeds are germinated - they make amylase to digest starch
Seeds are killed and dreid to make malt
Malt is ground up and mixed with water in a mash turn - amylase breaks down starch into maltose
Mash is boiled and filtered
Hops are added for taste and yeast is added to ferment sugars making beer
Beer is centrifuged + filtered
Beer is put into casks or barrels

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