Some of us (or perhaps only I) are attempting to culture our yeast starters in a respiratory state (with high oxygen and low glucose concentrations). In my experience, I cannot deliver very much air to the spinner culture using an aeration stone without creating too much foam. I have made several beers with poor head retention when I've included FermCap in the starter in sufficient quantity to prevent foaming in the aerated starter, so I've tried another method that does not require FermCap. I have been pumping filtered air at 2 liters/minute into the head space of a spinner culture with vigorous stirring.

Questions:

1. Can pumping air into the head space with vigorous stirring provide sufficient oxygen to the yeast to maintain them in a respiratory state during incremental infusion feeding?

2. Can FermCap be used in aerated starters without detrimental effects on the beer?

-Fred L. Johnson

RESPONSE:

If your starter culture tank is 10 feet tall the answer is probably not. If it is several inches tall and a wide surface area, the answer is yes. A sterilized cotton plug should allow enough air transfer to the surface of a stirring wort culture to provide enough O2 for the yeast. Pumping a small stream of filtered air into the head space would help.

I am not familiar with the composition of FermCap. Some antifoam compounds interfere with the oxygen transfer from the air into the wort media. Stirring via a magnet stirrer should minimize or eliminate any foaming problems.

Dr. Clayton Cone