What causes a blow-off...

[McAle]

I know its pressure build up but what causes it in some batches and not in others? Are some styles more susceptible to it than others?

 

[cluckk]

There can be many contributing factors: temperature (even warm or cold spots in your fermentation area), vitality/type of yeast, amount/type/ratio of sugars, adjuncts used, etc. Two beers, otherwise identical, may have very different fermentations because of some unknown variable between the two.

 

[BobbiLynn]

The yeast is an alive living organism(s). Over-pitching yeast is the most common reason for a blow off. Every batch of yeast will be different, even if it's the same kind. Temps, all that.... so many variables....

 

[unionrdr]

It's not overpitching that most often does it. Not at all. It's when you pitch a healthy yeast at around the same temp as the wort so it doesn't shock. Then that wort temp has to be in the middle to high end of the yeasts range.
It's pretty rare for the yeast to need a blow off when temp is at the low end of the yeasts range. This effects the lag time,that time where the reproductive phase is in full swing. It goes by quickly,& visible fermentation starts with vigor. this is the point where you se krausen slowly filling the airlock,& you start thinking,WTF? It will typically last for the duration of initial fermentation.

 

[BobbiLynn]

Oh, I always pitch yeast at the same temperature as the wort! Thought that was how you did it. And that's why it gets so crazy in the beginning many times?

 

[BobbiLynn]

Anyway, I always pitch the yeast when it's the same temp as the wort and only sometimes experience a blow-off. That's when I've pitched too much yeast.

 

[unionrdr]

Yes,pitching starters or rehydrated yeast at the same temp as current wort temp,or within 10 degrees will keep the yeast healthy & not "shock" them. They say thanks by going hog a$$ wild in your wort. But get the wort temp beyond that ten degrees (colder),& not overpitching as one would with lagers will negate blow offs by & large.

 

[freisste]

And from a completely different perspective, a large enough headspace will keep blowoff a from occurring.

But I agree with what has been said earlier and I am guessing they have given the answers you were more interested in.

 

[NordeastBrewer77]

Blowoffs just happen, that's about it. Yeah, some yeasts are more likely to show a large krausen and blowoff, others aren't. Pitch rates may have a bit to do with it, but unless you're throwing the wort onto an entire cake, that's not really going to be the cause. What I've noticed is that high gravity brews and fermentations that are too warm are more likely to blow off. All this about pitching within ten degrees and whatnot is just guess work... pitch yeast when your yeast and wort are both at fermentation temps, that's how ya do it, and be ready to use a blowoff tube because sometimes yeast does what ya don't want it to do.

 

[william_shakes_beer]

Short answer, blowoff occurs as the result of vigorous fermentation. If you want to reduce blow off, slow the action of the yeast by either pitching less or dropping the ferm temp to the lower end of the published range. I have found that recipies including large proportions of simple sugars will blow off more. I have a Raison D'Etre clone that uses Belgan Candy sugar and blows off an incredible amount. FYI, I have had only 1 or 2 batches that needed a blowoff tube since switching to a chest freezer ferm chamber.

 

[NordeastBrewer77]

Not that it's for everyone, some don't like using things like it, but Fermcap-S is a great product IMO and experience. Couple drops per gallon into the fermenter combined with restrained temps keeps krausen down significantly. I still keep a blowoff tube on for the early part of fermentation, but I have not had any blow off since I began using it.

 

[McAle]

Thank you everyone. Learned a lot. I appreciate the input.

 

[dadshomebrewing]

i'm pretty sure swmbo would give me an unprintable answer to this question