Originally Posted by david_42
No, bittering only occurs in the boil.
Most commercial operations use a blow-off of some sort, unless they are doing open fermentation.
Hop alpha acids are only isomerized in the boil to become bittering iso-alphas, but it's wrong to assume that you can't lose iso-alphas post-boil. At least, according to Palmer, yeast can force as much as 40% of dissolved iso-alphas to precipitate. According to Daniels, blow-off can result in losses of up to to 15% total iso-alphas.
I think you're confusing "blow-off" with standard airlock offgassing. Fermentation blow-off is the result of fermenting in a vessel that is too small to contain the resulting krausen. It's a fault, not a feature (unless you're Bass Ale, and they recover the beer). I've toured many commercial operations, and I've not yet seen one that seeks to encourage blow-off .
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