Fermcap in kettle = blowoff in fermenter?

[QuercusMax]

This past weekend I did two ten-gallon batches, and in both of them I used Fermcap to prevent boilovers. It did an admirable job! Everything hunky-dory.

First batch was an Extra Pale Ale, which I put into 2 6.5-gallon buckets. One got some harvested US-05, the other got fresh S-04. I pitched at 60F on Saturday and it's now around 63F - and this morning it had fouled my airlock. I've *NEVER* had a batch with US-05 blow off like this.

The S-04 hasn't blown off yet, but it also got about a half-gallon less wort, plus it was an un-rehydrated packet, so that may be fine.

Second batch from Saturday was a dortmunder-type wort, which I split into 5 gallons US-05 (repitched) in a bucket, 3 gallons each of WLP029 Kolsch and W34/70. Yesterday the Kolsch was going crazy at 61F, threatening to foul my airlock, and the US-05 (at 60F!) already did. I brewed the exact same recipe with the US-05, and hit the same gravity numbers a month ago, and didn't get any blowoff.

This morning I checked on the lager yeast, which had been taking a while to get going (I pitched at 5C on Sunday morning, and warmed up to 11C over 2 days), and this morning it was about to foul my airlock too!

Now, my solution to all of these is simple - add fermcap to the fermenter as well.

But in 10 years of brewing, the only blowoffs I've ever had have been with WLP530 and WLP300, or when I intentionally overfilled a 3-gallon carboy (and put in a blowoff tube since I knew it was going to blow). It's especially crazy to me that both batches I made with fermcap in the kettle are blowing off. When I made the exact same recipes (with virtually identical grainbills - the Dortmunder is exactly the same, and the only difference with the XPA is I changed from 40L Caracrystal Wheat to 60L Crystal) before, with the same yeasts, and fermented at the same or warmer temperatures, I didn't get blowoffs!

Anybody else experience something like this?

 

[wardens355]

I use Fermcap during the boil to prevent boilover and I still have occasional blowoffs. If I am concerned about blowoff, I will add Fermcap to the fermenter after I pitch, but I always start fermentation with a blowoff tube rather than a small airlock. Maybe you have some especially healthy yeast this time around. The addition of Fermcap in kettle should not have anything to do with the blowoff.

 

[sandyeggoxj]

There are a lot of factors here. But I would bet that oxygenation and yeast health play into this the most. Did you oxygenate different? Add yeast nutrient? I run a blow off for every fermentation. But then again I'm using better bottles with only .5 gallons of headspace.

 

[QuercusMax]

For the brews in buckets, I aerated with a wire whisk. I shook the carboys for 30 seconds to aerate. No yeast nutrient used.

I'm going to keep track of whether I use fermcap or not in the boil, and see if that has any correlation with crazy blowoff in the fermenter... could just be a coincidence in this case.