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Old 03-03-2011, 11:56 PM   #1
MooDaddy
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Default Blow off valve - please explain when and why to use?

I have just recently bottled my first home brew - a double chocolate stout - so I am as green (excuse the pun) as it gets with the brewing process.

Questions: I have heard numerous references to something called a blow off valve.

1. What is it specifically?

2. How do you know when you need to use one?

3. When it is called for, how long does it stay in place?

4. Are some brewed beers more prone to needing one than others?

Thanks

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Old 03-04-2011, 12:06 AM   #2
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I think what you are referring to is more commonly called a blow-off tube. Basically, it's just a tube coming from the neck of your carboy into a jar of sanitizer. It's a way of handling fermentations throwing off more krausen than an airlock can accommodate. How often you need them depends on a lot of factors, including the size of your carboy, etc. If you start getting jammed up airlocks, it's something worth thinking about. Some people use them every fermentation, others less often. Beers that are big, pitched with a high amount of yeast, and pitched warm will tend to need blow off tubes more often. Good luck!

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Old 03-04-2011, 12:12 AM   #3
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1. A blow off valve is a sanitized tube that you stick into the top of your carboy, then stick the other end into a jar of sanitizer solution, which acts as your airlock.
2. You use one if you are doing, say, a five gallon batch in a five gallon carboy (as opposed to 6-6.5 gal, with which you don't need a blow off tube at all), because the krausen will often bubble so high that it get into/out of the airlock, thus with your blow off tube just carries some of the krausen off into the sanitizer. As the oils in cocoa tend to cause chocolate stout fermentations to have little to krausen, this was likely not an issue for you.
3. You usually keep it there until the krausen starts to fall, because after that there is no danger of the krausen getting any higher anymore.
4. Not really, it's more of a volume thing...however, certain Belgian/wheat beer yeasts are real "top-croppers" and get notoriously big krausens, so sometimes, even if you have a 6.5 gallon carboy, if you use Belgian yeast and have a good starter and your wort is *really* well aerated, you might want to use a blow off apparatus.

Hope this clears some stuff up! Happy brewing, and I hope the Dbl Choc stout comes out great!

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Old 03-04-2011, 12:15 AM   #4
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Do you generally need a blowoff tube when using a 6.5 gal fermentation bucket for a 5 gal batch? I'm brewing a bigger beer this weekend (Bourbon Barrel Porter, OG of 1.065, using a 2L starter) and am wondering if a tube would be a good idea in this situation. I know it's not a bad idea, but I don't currently have the tube, so I'm thinking I can get away without one here.

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Old 03-04-2011, 12:16 AM   #5
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Reading the above post answered most of my question. Would have been nice to read that before I typed all that out.

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Old 03-04-2011, 01:58 AM   #6
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Thanks, that explains a lot. One other question, does the blow off tube take the place of the air lock, or function with it?

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Old 03-04-2011, 02:09 AM   #7
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It takes the place of the airlock. Just make sure you have the end of the tube in a bucket of sanitizer. I make my blow off tubes using 1/2 inch interior diameter tubing with a number 10 rubber stopper drilled out with a 9/16 drill bit. It's a tight fit but Starsan makes it push in easier.

Also if you need to I think its a 3/8ths I.D. tube that can push into a #10 stopper. Really tight fit but a stopper and tube well soaked in starsan will fit together with some effort. I use this setup for secondary fermentations all the time. I rarely use an airlock anymore.

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Old 01-07-2013, 01:04 PM   #8
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Quote:
Originally Posted by cuttsjp View Post
1. A blow off valve is a sanitized tube that you stick into the top of your carboy, then stick the other end into a jar of sanitizer solution, which acts as your airlock.
2. You use one if you are doing, say, a five gallon batch in a five gallon carboy (as opposed to 6-6.5 gal, with which you don't need a blow off tube at all), because the krausen will often bubble so high that it get into/out of the airlock, thus with your blow off tube just carries some of the krausen off into the sanitizer. As the oils in cocoa tend to cause chocolate stout fermentations to have little to krausen, this was likely not an issue for you.
3. You usually keep it there until the krausen starts to fall, because after that there is no danger of the krausen getting any higher anymore.
4. Not really, it's more of a volume thing...however, certain Belgian/wheat beer yeasts are real "top-croppers" and get notoriously big krausens, so sometimes, even if you have a 6.5 gallon carboy, if you use Belgian yeast and have a good starter and your wort is *really* well aerated, you might want to use a blow off apparatus.

Hope this clears some stuff up! Happy brewing, and I hope the Dbl Choc stout comes out great!
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Old 01-07-2013, 03:10 PM   #9
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This post also shows an easy way to make one using a three-piece airlock and a short length of tubing. http://www.homebrewtalk.com/f11/what-size-tube-airlock-blowoff-62276/ This is the way I made mine. The airlock piece is dedicated to the blow-off tube (i.e. I don't reassemble it and use it as an airlock). I also clipped the little cross of plastic in the bottom of the airlock. I start EVERY beer on my blow-off tube, and only swap it out once I make my next beer (and need it for that one), or my beer has been fermenting a while, and I need to put an airlock on it to make it more mobile. As a new brewer, I would suggest you start with this practice of always starting with one, until you get a good feel of which brews will or won't need it, and such. A blow-off tube is just a giant airlock, so if it doesn't get in the way, etc. there's no harm in using one, even if you don't need it.

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Old 01-07-2013, 03:18 PM   #10
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In reply to the question of when, I suggest installing one, at least during the start, of every fermentation Do this unless you have a very large headspace to accept a large krausen.

It is not much more difficult to install a blow-off tube instead of an airlock and it is much easier than cleaning krausen off the ceiling if you needed one and didn't use it.

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