Yeast consists of microorganisms. As long as air and dissolved food is available they breath like other organisms.
In contrast to them yeast can live without air. Instead of respiration they perf.orm glosgaerungE.html:
Sugar dissolved in Cola is decomposed by chemical reaction producing cabon dioxide and alcohol.
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        a                               b                                    c                   d                  e
A08 Yeast fungi can live in Cola without air

Material (Abb. a, d, e)
Infusion bottle (50 mL), balloon fitting to the bottle, dispoable syringe (50 mL), pipette tip, ampoule (2 mL),
stale Cola (compare Cola light), yeast (dry or fresh), lime water.
Experiment (Abb. b)
1. Mix 40 mL stale Cola with 1 mL of yeast in an infusion bottle.
2. Close the bottle by an empty balloon in order to stop the air supply.
3. Leave the apparatus until no more change can be observed.
4. Transfer the gas from the balloon into the syringe.
5. Pump the through the lime water.
Observation (Abb. c)
After a short time a foam is built and a gas can be collected in the balloon.
This gas makes lime water milky.
Explanation
Yeast transforms sugar of Cola into carbon dioxide.

back..........................first publication: 25.10.2001............................................last modification: 12.01.2012