Blow-off tube vs. appropriately sized fermenter - Home Brew Forums
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Old 10-03-2013, 12:39 AM   #1
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So, I've wondered for a long time why some people preach that you should always, always, always use a blow-off tube. I think I've realized that they, for whatever reason, just don't use a big enough fermenter that allows the necessary head space for the krausen.

Obviously, there are exceptions to this. There is the occasional case of a beer fermenting wildly and over-flowing a fermenter which had previously provided adequate head space. Probably those cases can be blamed on some combination of over-pitching yeast, high fermenting temperatures, or some other mistake made by the brewer.

But why do people try to ferment a 5 gallon batch in a 5 gallon carboy? That doesn't make any sense to me. I mean, I know that when you have exactly 5 gallons in one of those, there is still a little bit of space left. But not nearly enough that I'd feel comfortable pitching yeast with it being that full.

I can't imagine that it is a matter of wanting to save space by using smaller fermenters, because that means you need something to catch whatever is coming out of the blow-off tube. So, you have an only slightly smaller fermenter, but an entirely separate container of some sort right next to it. Doesn't add up to saved space.

And also, don't you end up losing some of the final volume of the batch if it goes out through the blow-off tube? So, really, you end up wasting space where you could possibly fit another fermenter AND you end up wasting beer by inviting it graciously to go for a swim in some sanitizer.

I'm not aware of any beginner's equipment kit that comes with only 5 gallon fermenters. Except for small batch kits (Mr. Beer - 3 gallons? Brooklyn Brew Shop and other 1 gallon kits), they all come with at least one 6.5 gallon bucket/carboy, and then maybe a 5 gallon carboy to use as a secondary. So, it isn't a matter of newbies being led astray by the equipment they are introduced to as they begin the hobby.



Is there something I'm missing?


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Old 10-03-2013, 12:50 AM   #2
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I think you may be jumping to conclusions here. My guess is most brewers preaching use of a blow off tube are using 6 gallon fermenting vessels. I've had plenty of blown off bubblers on 6 gallon carboys when pitching a calculated amount of yeast under temperature controlled environment. I doubt it is a regular practice to primary ferment in 5 gallon carboys by most home brewers.



 
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Old 10-03-2013, 12:56 AM   #3
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I personally think that you have answered your own question(s). It could also be that "they" are also concerned about the possibility of infections in fermenters that have a lot of head space. I like the head space, that way I can harvest some of the yeast for later. The more money I save the more beer I can brew. It works well for me.

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Old 10-03-2013, 01:02 AM   #4
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Quote:
Originally Posted by geoffey View Post
I think you may be jumping to conclusions here. My guess is most brewers preaching use of a blow off tube are using 6 gallon fermenting vessels. I've had plenty of blown off bubblers on 6 gallon carboys when pitching a calculated amount of yeast under temperature controlled environment. I doubt it is a regular practice to primary ferment in 5 gallon carboys by most home brewers.
It may not be a regular practice, but I sure see a lot of pictures on this forum of 5 gallon carboys with blow-off tubes.

Quote:
Originally Posted by kev View Post
I personally think that you have answered your own question(s). It could also be that "they" are also concerned about the possibility of infections in fermenters that have a lot of head space. I like the head space, that way I can harvest some of the yeast for later. The more money I save the more beer I can brew. It works well for me.
Does the extra head space really contribute that much risk of infection?

I guess this is a hobby for which many of us do what we can with what we have. I just don't understand why the fermenter size is generally left out of the conversation when people start preaching about using blow-off tubes.
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Old 10-03-2013, 01:07 AM   #5
Keithww
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I use a blow off tube when I have a beer that is over 1.080 and I'm pitching a yeast that I have double stepped on the stir plate, even with the cooler set to the mid 60's I'm going to have krausen by the gallons.

 
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Old 10-03-2013, 01:08 AM   #6
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Ive recently had two batches (both 5.5 gallons in my 7 gallon fermenter) fully utilize the blowoff tue. Insane!

 
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Old 10-04-2013, 03:31 PM   #7
HopSong
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When I read these threads about needing a blowoff I wonder.. I've made some reasonably big beers of the 5G size and I use a Speidel 20L (5.3G) fermenter.. there is not a ton of headspace.. but, either I'm lucky.. or possibly it might be that I control my fermentation environment to 65* with a water bath.

I'm going to try to build a thermowell out of SS tubing to get a better picture of my actual fermentation temperature.. but, I'd think that controlling the temp has a lot to do with it. I'll be brewing a 2x IPA soon and I will be adding a blowoff tube.. just in case.. but, I doubt I'll need it.
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Old 10-04-2013, 03:43 PM   #8
reverendj1
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Blow-off tube preacher here. I use regular 6.5 gallon ale pales, and still start on a blow-off tube every single time and recommend others do too. It's not about using smaller fermenters. This is why:

Quote:
Originally Posted by signpost View Post
Obviously, there are exceptions to this. There is the occasional case of a beer fermenting wildly and over-flowing a fermenter which had previously provided adequate head space. Probably those cases can be blamed on some combination of over-pitching yeast, high fermenting temperatures, or some other mistake made by the brewer.
Yeast is a living thing. You can't say for 100% certainty that this batch will behave exactly like your last batch even with the same ingredients/process. I've had my blow-off tube actually get used (as in got blow-off) only a few times in ~40 batches, but using it every time saved me from cleaning up those few times. Some of those times may have been a mistake by me (I'm not perfect) or my equipment, who knows, but it's cheap insurance and has no real downsides.

 
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Old 10-04-2013, 03:50 PM   #9
Pilgarlic
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I use a 6 gallon fermentor. I always use a blow-off. Why not? It's no trouble.

 
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Old 10-04-2013, 04:17 PM   #10
eltorrente
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As far as infection possibility and headspace are concerned, it isn't a factor IMO. I've been brewing for over 17 years, and never once had an infection from all combinations of carboy and wort volume. It just isn't a factor.

I don't even bother with blow off tubes nowadays unless I'm using a 5 gallon carboy and a 5 gallon batch. I use Fermcap, so blow-offs and boil-overs are a distant memory. I like using 6 and 6.5 gallon carboys for my 5.3 gallon batches, and the extra head-space is a good thing. Sometimes I get a couple inches of Krausen, but it never threatens a blow-off.



 
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