Ask Mr. Wizard

Blow off the kräusen?


Roger Swantek • Clinton Township, Michigan asks,

Is it better to blow off during primary fermentation or use a closed system so the debris from high kräusen settles back into the carboy or conical fermenter? Does filling a carboy within one inch of the top and inserting a blow off tube lead to the expulsion of yeast that may degrade the remaining yeasts’ ability to reach the desired terminal gravity? Does blow off affect hop presence in regard to aroma or bitterness?

For a closed fermentation, a stainless steel conical fermenter with a domed lid seems like a good choice as it does not seem prone to blow off due to its large head space thereby allowing the homebrewer to completely fill the fermenter. A fermenter with a flat lid, with very little headspace, when filled to capacity, appears more likely to blow off since it has little or no headspace when filled.

Some of our primary fermentation carboys blow off very aggressively and terminal gravity is in the 20 to 30 range. If one of ours blows off less (with little or no debris leaving the carboy), it seems as if TG is lower — more in the 08 to 12 range. Would blow off cause the variability?

Most of my beers are mashed somewhere between 150 and 152 °F (65.5 and 67 °C) and initial gravities are rarely lower than 1.070. Target terminal gravity is 1.010 or less and little if any crystal malt or unfermentables which would result in a higher terminal gravity are used. My club and I use liquid yeast with a starter and visible fermentation starts in less than eight hours in all cases. We infuse oxygen in each carboy with our recipe kits from disposable oxygen tanks (20 second infusion).

  This is a classic question about brewing technique. Allow me to give a little background on the technique of fermenter skimming used by some traditional brewers using open fermentation tanks. Traditional,
Response by Ashton Lewis.