Unraveling The Mystery: Beer Yeast's Rapid Reproduction Rate

Beer yeast grows rapidly when there is oxygen in the brew, and almost exponentially. However, when there is no oxygen, the yeast growth slows down and almost stops.

Aerobic phase: rapid increase in yeast

Yeast multiplies rapidly when it has oxygen available. This is the aerobic phase, where there is a rapid increase in yeast and an almost exponential growth of yeast. During the aerobic phase, there is a presence of oxygen in the brew. Yeast absorbs any oxygen and nutrients you have added at this point to fuel its growth. Carbon dioxide activity also increases rapidly during the growth phase. CO2 activity peaks near the point of peak growth, though CO2 will continue to be produced as long as active fermentation continues. The gravity of the wort does not drop much during the initial cell growth phase, though it will start to drop more rapidly once peak cell activity is reached. It is not unusual to see a kind of exponential decay beyond that point as the sugars are consumed rapidly past peak cell levels and then gravity decline slows as fewer fermentable sugars are available.

Anaerobic phase: yeast growth slows

During the anaerobic phase, there is an absence of oxygen, which causes the yeast growth to slow down and almost come to a halt. Yeast does not grow well anaerobically but needs the presence of oxygen to grow. The yeast will absorb any oxygen and nutrients you have added at this point to fuel its growth, which is why aeration is important. Carbon dioxide activity also increases rapidly during the growth phase, though it does trail off slightly as fermentation progresses. Typically CO2 activity peaks near the point of peak growth, though CO2 will continue to be produced as long as active fermentation continues. The gravity of the wort does not drop much during the initial cell growth phase, though it will start to drop more rapidly once peak cell activity is reached. Its not unusual to see a kind of exponential decay beyond that point as the sugars are consumed rapidly past peak cell levels and then gravity decline slows as fewer fermentable sugars are available.

Oxygen: fuel for yeast growth

Yeast multiplies rapidly when it has oxygen available. 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 of oxygen, this causes the yeast growth to slow down and almost come to a halt. This is because yeast does not grow well 'anaerobically' but needs the presence of oxygen to grow. The yeast also will absorb any oxygen and nutrients you have added at this point to fuel its growth, which is why aeration is important. Carbon dioxide activity also increases rapidly during the growth phase, though it does trail off slightly as fermentation progresses. The gravity of the wort does not drop much during the initial cell growth phase, though it will start to drop more rapidly once peak cell activity is reached. Its not unusual to see a kind of exponential decay beyond that point as the sugars are consumed rapidly past peak cell levels and then gravity decline slows as fewer fermentable sugars are available.

Exponential growth: rapid yeast increase

Yeast multiplies rapidly when it has oxygen available. 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 of oxygen, this causes the yeast growth to slow down and almost come to a halt. This is because yeast does not grow well anaerobically but needs the presence of oxygen to grow. The yeast also will absorb any oxygen and nutrients you have added at this point to fuel its growth, which is why aeration is important. Carbon dioxide activity also increases rapidly during the growth phase, though it does trail off slightly as fermentation progresses. Typically CO2 activity peaks near the point of peak growth, though CO2 will continue to be produced as long as active fermentation continues. The gravity of the wort does not drop much during the initial cell growth phase, though it will start to drop more rapidly once peak cell activity is reached. Its not unusual to see a kind of exponential decay beyond that point as the sugars are consumed rapidly past peak cell levels and then gravity decline slows as fewer fermentable sugars are available.

Stirring: aids yeast growth

Yeast multiplies rapidly when it has oxygen available. 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 of 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.

Stirring is a way to give your must oxygen by rapidly stirring it for a couple of minutes. This is mostly done when making beer where you don't want to risk any infections but I have also never needed to stir a still wash. As I understand it, it is one or the other. I don't think you should stir to aerate after the first time.

The yeast also will absorb any oxygen and nutrients you have added at this point to fuel its growth, which is why aeration is important. Carbon dioxide activity (blue line) also increases rapidly during the growth phase, though it does trail off slightly as fermentation progresses. Typically CO2 activity peaks near the point of peak growth, though CO2 will continue to be produced as long as active fermentation continues. The gravity of the wort does not drop much during the initial cell growth phase, though it will start to drop more rapidly once peak cell activity is reached. Its not unusual to see a kind of exponential decay beyond that point as the sugars are consumed rapidly past peak cell levels and then gravity decline slows as fewer fermentable sugars are available.

Frequently asked questions