What causes blowoffs?

[gratefuldisc]

I just put my second batch in primary about 28 hours ago and I am trying to RDWHAHB but all these stories and photos have me nervous about explosive blowoffs. What factors contribute to overactive yeasties? certain styles, yeast strains? overpitching? warm temps? anything else?

Basically trying to decide if I should drive to my father-in-law's where my fermenters are to change out the airlock to a blowoff tube...

Its a robust porter 1.055 OG, dry (I rehydrated) coopers yeast, 6.5gal Ale Pail with 3 piece airlock, sitting in a swamp cooler with a fishtank heater maintaining 68. My FIL says its bubbling once a second. I really don't want to make a mess in his basement, he wont care but my MIL will freak.

 

[the_bird]

Hard to generalize too much. Obviously, less headspace is bad. Really active fermenations (which can be caused by warmer temps) are more likely to make a mess. I'd wager that beers with a higher protein content might be more apt to blow off - same things that cause beer to have good head retention would seem likely to cause problems in the fermenter.

Lots o' folks swear by Fermcap, both in the boil kettle and in the fermenter, to limit the risk.

 

[GilaMinumBeer]

What causes blowoffs? Bad piuck up lines!

And not enough headspace.

 

[Yooper]

I've only had one beer that absolutely needed a blow off tube. It was a beer with some wheat, in the heat of summer, and I pitched on a yeast cake. It was almost impossible to keep that baby under 70 degrees once it started roaring!

Generally, the reasons you mentioned cause blow offs. Pitching hot, and allowing the beer to get too hot, proteins (wheat beers are more likely to have issues), and too-little headspace, along with more fermentables will tend to have more blow-offs than cooler, lower OG ferments.

 

[Malticulous]

Yeast. 234

 

[C2H5OH]

In a word: Over-stimulation.

Just keep thinking:
Margaret Thatcher in a thong.
Margaret Thatcher in a thong.
Margaret Thatcher in a thong.
Margaret Thatcher in a thong.
Margaret Thatcher in a thong.
...