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Blow off

Wfu1bunn

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Sep 29, 2014
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Fermentation my last 2 batches has been so vigorous it blows off the airlock. What should I do differently?
 
Attach a blowoff hose to the airlock (you need the three piece variety, but don't use the cap and cover) and run the hose to a small bucket of starsan.
 
Blow-offs often indicate you are fermenting too warm. I believe I get better beer by fermenting at the bottom of the yeast manufacturer's stated temperature range - sometimes even a couple of degrees below the stated range. Fermentation will take a little longer and I don't guarantee you won't still get a blow-off, but the risk is reduced.

It also helps to use a fermenter with lots of headspace, like five gallons of beer in a 6.5-gallon bucket, one gallon in a 2-gallon bucket, etc.
 
I believe I get better beer by fermenting at the bottom of the yeast manufacturer's stated temperature range - sometimes even a couple of degrees below the stated range.

I agree.
 
I had this happed a few times b/c the airlock clogged.  I cut the tip off so the opening is bigger and I helped with the clogging.  Also, you might need more head space in the fermenter.  The tube suggestion works too, might want to put the open end in a glass of sanitized water
 
The blow tube can be a tube with an outside diameter the same as the inside diameter as your carboy neck.  This allows you to just push that large diameter hose into the carboy neck and let it hang down into StarSan water in a bucket or blow.  The open end of the tubing should be about 2" below the surface of the StarSan water.

You will not have this approximatley 1.5 inch tubing clog, which is the advantage.

The drawback to this is that as it blows off, it's taking potential beer out with the krausen, so you end up with less volume.  I've lost as much as a half gallon of beer through my blow off tube.  My solution is an 8 gallon bucket fermenter (with a standard airlock) for 5 gallon batches.  I've never had one make it up to the airlock and clog or force the airlock out when I had all of this headspace.

Headspace usually equals oxygen that can cause off flavors.  But in this case, it isn't an issue, because during high krausen the yeast are creating a lot of CO2 which keeps the oxygen out.  Once primary fermentation slows down to a crawl, it's probably a good idea to move the beer into a carboy with less headspace.  However, I have left them in the large bucket and have never noticed off flavors due to the large headspace.
 
I started using a blowoff tube soon after I started doing yeast starters. I had two batches clog the bubbler and blow the lid off the fermenter. I bought another lid for the plastic fermenter and got some food grade tubing at Lowe's. Then drilled a hole the exact size as the outer diameter of the tubing into the lid (make sure it is well above the wort.) The other end of the tube goes into a container (I used a quart jar) that has a water sanitizer solution in it and then just put the end of the tube into the jar. I only cover the tube about 1/2 inch or in the solution. The deeper you put it the more back pressure you will get in the fermenter and I'm gun shy from the bubbler blowing off the lid previously. Once the fermentation dies down a bit I may put the other lid with the bubbler on the fermenter and then I don't have to keep checking the blowoff tube.
 
When I know that I don't have enough headspace in my fermenter (sometimes I run-off too much) I like to use a little Fermencap-S.  It keeps the krausen down and eliminates the need for a blow-off tube.  As an added bonus, I feel like I get better head retention in my beers.  But, if you don't want to go that route, make sure you have a good amount of headspace in your fermenter, lower your fermentation temp (if you can) and use a blow-off tube.  I use a 1.25" OD hose stuck into the mouth of a glass carboy and stick the other end in a bucket of StarSan.
 
Sometimes blow offs are not due to fermentation temperature. Headspace always makes a difference, but something always overlooked is the ingredient list. I haven't figured it out yet, but I'm finding certain ingredients often cause a blow off for me making 5 gallon batches using a 6.5 gallon bucket. Yeast strain matters, too. I threw out temperature as being the main factor after blowing the air lock off a batch fermented cold, using a nearly expired smack pack that was already swollen, all in a batch under 1.045 starting gravity.
 
I also feel that blow off tubes are the way to go.  As stated make sure you use a primary fermenter that has plenty of head-space. 
 
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