As others have mentioned, thank you very much for the opportunity... My question is on yeast cell counts within a starter. Assuming one began with a 1L of 1.040 starter wort, and 50 ml of yeast containing 15 billion cells that has an Apparent Attenuation of 75%:

1) What would the cell count be in the starter if allowed to go to completion? How about with a 2L starter of the same gravity?

2) What would the cell count be in the starter if continuously stirred and allowed to go to completion? How about with a 2L starter of the same gravity?

-Mike Dixon

RESPONSE:

This is not an easy question to answer. There are too many variables.

1. 50 ml. of yeast containing 15 billion yeast cells = 300,000,000 yeast cells per ml. That is a remarkable amount of yeast per ml. to start with. I assume that this initial quantity of yeast came from a yeast cake that you dissolved into 50 ml. When you add this to 1 liter you will then have 15 million yeast cells per ml.

When you add it to 2 liters you will have 7.5 million yeast cells per ml. . If there is adequate nutrients in the wort there should be 100 - 150 million yeast cells per milliter when the yeast reaches the stationary phase. This should hold true for both the 1 liter and 2 liter starter culture. With low levels of nitrogen, minerals and vitamins, this count be reduced by 50%. Yeast strains can make a difference in the growth rate and final numbers at the stationary phase.

2. Aeration and stirring can increase the cell count by 50 to 100%. I wish that I could be more precise.

Dr. Clayton Cone