Expert: Ed Westemeier - 10/26/2009

Question
I just finished racking my second batch of homebrew (and IPA) to the secondary.  The wort spend 6 days in the primary until the  vapor lock bubbled every 2 1/2 minutes or more.  SG went from 1.046 to 1.017.  I though it was ready, tossed 1 oz. of Cascade plugs in and siphoned into the secondary.  Almost immediately, an extremely active fermentation began, to the point where the vapor lock was filling with beer and overflowing.  After 6 hrs. it calmed down and is not bubbling about once every 1 1/2 minutes.  What caused this?  I believe the vapor lock overflowed because I didn't leave enough room in the Carboy for hop expansion and they filled the carboy's neck, but the reactivation of the fermenting process took me by suprise?

Answer
Don't worry -- that's not surprising at all.

Your primary fermentation was fine, since you got down that far. Fermentation was not complete, since your airlock was still active. When you moved it to a secondary fermenter, you introduced a small amount of air, and also roused the yeast. The combination of new oxygen from the air and stirring some of the yeast back into solution had the effect of making the fermentation more vigorous.

The expansion of the hop plugs was also a factor. Next time, consider using a hop bag and weighting the bag with a few marbles to make it sink (boil the bag and the marbles first).

Enjoy your ale. It would probably be considered an American Pale Ale, since your starting gravity was not really high enough to be classified as an IPA (they start at about 1.056 and go up from there).