Do yeast multiply in the initial aerobic phase or do they continue to multiply all the way through the entire anaerobic phase?

2 Answers 2


During the aerobic phase there is a presence of oxygen in the brew, during this phase there is a rapid increase in yeast and an almost exponential growth of yeast. During the anaerobic phase there is an absence oxygen, this causes the yeast growth to slow down and almost come to a halt. This since yeast does not grow well 'anaerobically' but needs the presence of oxygen to grow.

  • So they just about get by anaerobically, but are not thriving enough to multiply. I guess this really shows the importance of aerating your wort. Commented Jan 22, 2014 at 12:14
  • 1
    Yupp, it is really important to provide enough oxygen for the yeast to grow. I wonder if there is a possibility to increase the aerobic phase by introducing extra oxygen from, let's say, a tank...? Will have to do some more reading :)
    – Sander
    Commented Jan 22, 2014 at 12:58
  • Thanks! (I will just place some more text here so that I am able to comment and thank you for the link.)
    – Sander
    Commented Jan 22, 2014 at 13:30

You might be interested to look up Krebs cycle and the electron transport chain which yeast follow when in its aerobic respiration phase. This is when the yeast can create a ton of energy and that surplus of energy is used to replicate.

After the oxygen runs out, it goes into anaerobic processes where the yeast produce CO2, ethanol, and sometimes lactate depending on the yeast or bacteria.

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