OK. Racking and cleansing gravities. God, we discuss such fascinating stuff.
Here's what Barclay Perkins did:
For Ales, the difference varies from 2 to 5 degrees. For the Stouts, the difference is bigger, 4 to 8 degrees. Though that does include IBSt, which had an OG of more than 1100.
If one assumes that the beer is racked three or four points above final gravity, then it seems that the cleansing gravities were reasonably high, or high enough. It depends, of course, upon what system of cleansing the respective brewers used, but generally the beer must still be in active fermentation to keep the yeast buoyant and to develop the gas pressure necessary to push the surplus yeast out of the cleansing casks.
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