why a blow off?

what happens if foam goes up into my airlock? is it bad?

Beer is good said:

what happens if foam goes up into my airlock? is it bad?

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No, it's not "bad", it may be messy, however, especially if it becomes so forceful it blows off your airlock or spits out of your airlock.

That being said...I've gotten krausen in my airlock a few times, and I've never used a blow off tube. My primary is 6.5 gal, so typically I have enough space. Whenever it does get into my airlock, I gently remove it, quickly clean it, refill it and replace. It's never done that more than 3 or 4 times.

Yes, it is bad. If it clogs up the airlock, it is possible that gas will not be released from the fermentation vessel, and it could explode.

It's good to have a spare airlock or two. They are cheap. Sanitize a spare and replace the clogged one whenever you see this occur. Having a spare lets you swap them without leaving the bottle open for long enough to risk contamination while you're cleaning out the dirty airlock.

If your fermentation is very active and a lot of foam is coming up through the airlock, just a blowoff tube instead. It's a vinyl tube that fits into the carboy opening. Run it into a bucket of water. This is, effectively, a really big airlock.

beer4breakfast said:

Yes, it is bad. If it clogs up the airlock, it is possible that gas will not be released from the fermentation vessel, and it could explode.

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Explode? Your airlock would shoot off before that would happen. And you'd have to have some major hard CRUD in your fementer in order for it to completely clog your airlock. Usually it just joins up with the water/vodka/sanitizer in the airlock and spits a bit out. Never had a clog or lack or gases moving, and definately not an EXPLOSION of my fementation vessel.

I've read that it can explode:

Bodensatz Brewing

Tofi's collected home-brewing techniques

Google it. There are a few people who claim to have suffered such a fate, and many many more who state that it is a possibility.

Well an explosively shooting airlock maybe. Had that happen years ago on one of my first brews. 6.5 gallon plastic carboy, plugged airlock. Presure can really build in those plastic carboy and kabam, airlock hit the ceiling and shot hoppy beer foam all over the ceiling for like several minutes.

I wasn't home at the time but my Mom and brother were. hehe.

Ah, the good ol' days.

You'd have to have your airlock glued down and clamped to the carboy to make the carboy explode.

I haven't had a fermenter explode, but having the lid blow off of a bucket when the airlock clogs is close enough!

Since carboys aren't designed to hold pressure & glass loses strength with the tiniest of flaws, I could see how a carboy could shatter with only one or two PSI in it.

david_42 said:

I haven't had a fermenter explode, but having the lid blow off of a bucket when the airlock clogs is close enough!

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That's what I think most see as an "explosion". Some people are too literal.

I got a friend into the hobby a couple of months ago. He brewed AHB's Cannonball Stout. It "exploded" and sent black wort all over the closet. His wife wasn't too happy with his new hobby.....