Recently many homebrewers have purchased or fabricated conical fermenters that employ 60 deg sloped sides & a bottom dump port. My questions are as follows:

1) Assuming normal yeast fermentation temperatures are employed - How many days of fermentation should occur before a brewer dumps yeast for reuse ?

2) Will the pressure that builds up on the condensed yeast cake at the bottom of the conical fermenter over the fermentation cycle damage or harm future harvested yeast? If so how?

-Bob Fawbush

RESPONSE:

(1) Attenuation time depends on yeast strain, yeast health, wort gravity, mashing protocol and fermentation temperature. The yeast should not be settling appreciably until the end of the fermentation when all the sugar has been used up (attenuation). Then it begins to flocculate and settle out. The rate of settling is strain dependent, final gravity and how long and well you have stored the re-pitched yeast.

You should note the fermentation activity, CO2 bubbling. When the CO2 bubbling dramatically slows down and you are near or at final gravity the yeast begins to settle; three to five days depending on the temperature of fermentation; three days at 80F, five plus days at 60F. These are very broad suggestions. Be guided by the turbidity of the wort. If you can refrigerate the mash, the yeast will settle faster and you can begin to remove the settled yeast. Refrigeration places less stress on the yeast to be used for the next pitching. Some beer makers will remove and discard the bottom 1/3 of the settled to get rid of most of the trub to minimize the carry over in the next re-pitching. The remainder should be removed ASAP and refrigerated at <4C. if possible. I wish there was a more definitive answer.

(2) CO2 should present no problem in the fermenter size that the average home brewer would use:

CO2 @ 0.2 atmospheres pressure stimulates yeast growth.
CO2 @ 0.5 atmospheres pressure begins to exert a negative effect on yeast growth.
CO2 @ 3.0 atmospheres pressure stops growth
CO2 @ 3.0 atmospheres pressure does not stop fermentation-alcohol production.
10 ft. height fermenter = 0.3 atmospheres.

Dr. Clayton Cone