Yeast is a single-celled organism with a nucleus, cytoplasm, cell membrane and a cell wall.
When O2 is present they respire aerobically and reproduce quickly.
However, when O2 is not present they respire anaerobically and produce ethanol and CO2 . This is called fermentation.
Making beer from yeast:
- starch in barley grains is used as the carbohydrate energy source
- starch is broken down into sugars in the barley grains by enzymes during the germinating process
- when there sugars have been fermented hops are added to give flavour
- beer is pasturised before sold to kill microbes
Making wine from yeast:
- fruit is crushed this gets juice and sugars out of it
- not always necessary to add yeast (there's natural yeast in fruit), yeast is needed as an energy source
- after fermentation the wine is cleared, stabilised and matured
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