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Blowing Off Kreusen
Grape Nuts Beer
The Kreusen Blow-Off
When a beer has a vigorous fermentation, the kreusen, or foam, that forms may cause enough pressure to cause a stopper and fermentation lock to blow right off the fermenter. The foam then proceeds to spill all over your floor and makes quite a mess. I recommend attaching a wide food-grade tube to the top of your fermenter for the first 2 to 3 days, with the other end in a clean bucket, until the foamy kreusen begins to recede. Allowing the top of the kreusen to escape through the large tube also improves the flavor of the beer and may reduce hangovers.
I've found that when I use a six-gallon pail as a fermenter for a five-gallon batch, I can attach a fermentation lock as soon as the yeast is pitched and there is no significant blow-off.