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Old 12-19-2009, 04:13 AM   #11
PT Ray
Aug 2005
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Originally Posted by samc View Post
Some kind of on demand valve from your CO2 tank, not sure how but someone on HBT will figure it out or already does it.
We call that a regulator. You hit the nail on the head and didn't know it. You could just put a hose barb on your co2 line and put it in place of your air lock. Just set the regulator to a minimum and put the air lock back when it's chilled.

I just keep my air lock filled low enough that any negative pressure will only suck in a little air and not liquid.

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Old 12-19-2009, 04:15 AM   #12
denimglen's Avatar
Feb 2006
Auckland, New Zealand
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I was just thinking about this the other day actually.

Sanitary filter in place of the airlock is my answer. That only stops the liquid but may increase the gas exchange.

I really think the small amount of O2 going in won't matter. If you're not transferring with CO2 it'll pick up way more O2 when you open the carboy to rack to keg, even more if you use a bottling bucket.

I think the only way to avoid it easily would be to use a fermenter that the walls won't collapse with vacuum and then completely shut it off to the atmosphere when you chill it. Could be quite easy if you used a normal rubber bung in a glass carboy, used a ball valve with a hose tail on each end, push one tail into the bung and then run a tube from the other to a normal blowoff. Then just turn the valve when it comes to cooling time.

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Old 12-19-2009, 04:45 AM   #13
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Aug 2006
Whitehouse Station, NJ
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It's not so much oxygen I'm worried about. It's the potential contamination inside my old nasty fermentation fridge. If you put vodka in the airlock, it's true there's no problem with liquid being sucked in, but there's also quite a bit of air going in with it after the level drops enough.
I'm trying to think of something simple but effective here and I'm not sure leaving my co2 bottle hooked up is fitting the bill. Thinking...
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Old 12-19-2009, 04:48 AM   #14
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Jun 2008
The Cold Part of AZ
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Originally Posted by Bobby_M View Post

I'm trying to think of something simple but effective here and I'm not sure leaving my co2 bottle hooked up is fitting the bill. Thinking...
I usually don't cold crash, and never lager, so it's not much of an issue for me; but, how much is "sucked back" during an usual cold crash?

Could you just fill the airlock completely full? Or get a bigger airlock or something that you could fill more? Or will the physics of the suck back drain the liquid to get to air, no matter how much liquid it needs to suck?

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Old 12-19-2009, 04:57 AM   #15
Nov 2009
New York, NY
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I would not worry about it. From now on your beer will be cold, and nothing will grow fast. From a yeast biologist point of veiw...you got a lot of limiting factors for infection. Alcohol and yeast is your number 1 and 2. Vodka or star san is your best bet in an air lock.

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Old 12-19-2009, 05:53 AM   #16
Nov 2009
Pasadena, CA
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Can you just take the negative pressure depending on your fermenter? Pop off your airlock and jam a rubber stopper in the neck of the carboy.
Modifying the ideal gas law (be prepared for liberal rounding):
P1/T1 = P2/T2, initially you are at atmospheric pressure and say 68F
1 atm/68F = x/34F, x = 0.5 atm. (convenient numbers )

So we are talking about going from atmospheric pressure (14 psi) to 0.5 atm (7 psi). Effectively a -7 psi pressure in your fermentation vessel upon cooling.

MATH FAIL: Didn't use absolute temperature. Correction posted here. <-1 psi change in pressure.

Does this seem like too much negative pressure on a glass carboy?

A Better Bottle would probably collapse a little bit. The change in volume necessary to equilibrate the pressure would depend on the headspace. Smaller headspace, less collapsing of the bottle.

Reason: Incorrect calculation.

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Old 12-19-2009, 06:26 AM   #17
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Jul 2006
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I'd figure out a way to rig up a sterile filter like this to the air lock

I'm pretty sure I've seen them for sale at some web homebrew store whose name is currently escaping me.

If you want to try this but can't track down a place that sells singles, let me know
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Old 12-19-2009, 02:48 PM   #18
Aug 2009
Atwater, OH
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Originally Posted by AZ_IPA View Post
for a split second, yes. But, the laws of gas exchange would dictate that the CO2 and O2 would mix evenly.

Interesting discussion point Bobby. I'd obviously thought of the liquid that's getting sucked back (no biggee with vodka), but didn't consider the air exchange.
Even if this did happen, I don't think there wouldn't be enough O2 to ruin your beer.

On another note, a sterile filter and check valve would probably satisfy those that are paranoid.
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Old 12-19-2009, 02:54 PM   #19
z987k's Avatar
Feb 2007
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you are worrying over nothing.

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Old 12-19-2009, 03:12 PM   #20
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Jun 2008
Elizabeth, CO
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If suckback really bothers you, use the "S" style airlocks for cold-conditioned beers.

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