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Old 07-04-2010, 09:59 PM   #1
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Default Beer degassing volcano -- why? Plus video.

In 70+ batches I have never seen this happen.

My Scottish 80 Shilling finished fermenting 2 weeks ago (confirmed by hydrometer, tasting, and dropped crystal clear). It has been bubbling slowly and steadily since, what I assumed was CO2 degassing. It has been at 77 F the entire time. The beer was racked from primary to secondary after about 3 weeks and dropped about 1 gravity point (1.016 to 1.015, the same gravity as my forced ferment test) during that secondary. The carboy was filled all the way to the neck.

Today for kicks I stuck my Reynolds Handi-Vac on the airlock mouth to see what would happen when I pulled a vacuum. A few seconds later, a rush of CO2 evolved from the beer and created a beer volcano out the the top of the carboy!

Here is a video of me doing this for the 4th and 5th times -- might want to turn your volume down, the pump sound is obnoxious.


I have now performed this 8 or 10 times, and I'm still getting a rush of CO2. I cut the vacuum as soon as I see it to avoid the ensuing volcano.

My question isn't why there's a volcano, it's why this particular batch has so much CO2 dissolved in it at room temp. My only guess is it's saturated, and with such small surface area in the carboy neck, the CO2 hasn't been "motivated" (for lack of a better term) to evolve on its own. But this doesn't seem like a great explanation to me.
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Old 07-04-2010, 11:46 PM   #2
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you do realize only a finite volume of co2 can dissolve in a liquid for a given temperature?

so i ask this: is the goal a still beverage? if not, you're wasting carbonation time.

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Old 07-05-2010, 04:36 AM   #3
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Still beverage is not the goal. But I do realize there are states of supersaturation, and that I don't have much knowledge of them, nor whether that is a possibility here.

Sure I'm wasting carbonation time. But if I don't know how much CO2 is in solution, how would I know the amount of priming sugar to use? Going off the basis that most of my beers have negligible CO2 dissolved, my priming sugar calculation won't be accurate.

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Old 07-05-2010, 05:00 AM   #4
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Doesn't seem like a supersaturation scenario. If that were the case once you started the vac all of the excess CO2 would rush out continually resulting in an overflowing carboy. You are just pulling CO2 out of solution, the "volcano" is more impressive looking than the amount of CO2 you are degassing.

At 65F you have 0.88 volumes of carbon dioxide dissolved which means there are 5.28 gallons of CO2 dissolved in your brew (assuming 6 gal batch size). That's a lot of gas

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Old 07-05-2010, 05:41 AM   #5
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Quote:
Originally Posted by greenbirds View Post
But if I don't know how much CO2 is in solution, how would I know the amount of priming sugar to use? Going off the basis that most of my beers have negligible CO2 dissolved, my priming sugar calculation won't be accurate.
Use any one of a number of carbonation charts available via Google, homebrewing forums, homebrewing books, etc. They work. Really. They work. Without degassing. Really.
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Old 07-05-2010, 02:30 PM   #6
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Use any one of a number of carbonation charts available via Google, homebrewing forums, homebrewing books, etc. They work. Really. They work. Without degassing. Really.
Look, I don't think I have an exception to the laws of physics here. I have a carbonation chart on my desktop and use it all the time. According to the chart, at 61 F (ferm temp), CO2 would be at 0.99 volumes. At 77 F (extrapolate past 70 F), it's approx 0.60 volumes, a difference of approx 0.4 volumes. What I'm curious about is what point the beer was at yesterday during that transition stage, which apparently can last for some time.

Let's say not knowing any of this I had removed the beer from he cooler, let it rise to 77 F for a day, and bottled targeting 2.2 volumes using Beersmith's calculator. Seeing how slowly CO2 was escaping this beer, I don't think it's out of line to assume it would not be close to equilibrium yet, and I would end up with closer to 2.6 volumes in the carbonated product. Too high for a Scottish 80. Maybe nit-picky, but if you're already at the high end of carbonation for a style, pushing it half a volume beyond is something to consider, IMO.
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Old 07-13-2010, 08:48 AM   #7
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You could get a Zahm and measure it that way.

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Old 07-13-2010, 01:57 PM   #8
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Appears to me that a good bit of that CO2 is going right back into solution, that 'head' falls extremely quickly.

Quote:
My question isn't why there's a volcano, it's why this particular batch has so much CO2 dissolved in it at room temp. My only guess is it's saturated, and with such small surface area in the carboy neck, the CO2 hasn't been "motivated" (for lack of a better term) to evolve on its own. But this doesn't seem like a great explanation to me.
The beer should be saturated with CO2 for it's temp (77* F), it's had yeast producing a lot CO2 and that CO2 will dissolve until the liquid is saturated (at that temp) and then the rest will just gas off. That's how the carb calculators work (they assume it's saturated for the temp given, which is why you use the highest temp the beer has been at). The beer just had the normal saturation level of CO2 for 77* F, which as you saw is more than we intuitively expect.

I think by pulling the vacuum several times (which I understand was just done for ****s and giggles) you now don't know what carb level you're starting with.

I prob didn't answer anything you didn't already know but I hadn't seen it expressed in those exact words so, there ya go.
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Old 07-13-2010, 02:14 PM   #9
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Quote:
Originally Posted by greenbirds View Post
Look, I don't think I have an exception to the laws of physics here. I have a carbonation chart on my desktop and use it all the time. According to the chart, at 61 F (ferm temp), CO2 would be at 0.99 volumes. At 77 F (extrapolate past 70 F), it's approx 0.60 volumes, a difference of approx 0.4 volumes. What I'm curious about is what point the beer was at yesterday during that transition stage, which apparently can last for some time.

Let's say not knowing any of this I had removed the beer from he cooler, let it rise to 77 F for a day, and bottled targeting 2.2 volumes using Beersmith's calculator. Seeing how slowly CO2 was escaping this beer, I don't think it's out of line to assume it would not be close to equilibrium yet, and I would end up with closer to 2.6 volumes in the carbonated product. Too high for a Scottish 80. Maybe nit-picky, but if you're already at the high end of carbonation for a style, pushing it half a volume beyond is something to consider, IMO.
CO2 is at a certain volume solution based on the beer temperature and standard pressure. It only takes a day or so for that to stabilize once the beer has reached a given temperature.

You're lowering the pressure, which lowers the amount of CO2 that can stay in solution. Now that you've done that, there's going to be less CO2 in there than the charts would indicate for a beer that reached 77F. Unfortunately you have no way of measuring how much CO2 you pulled out of solution, so standard carbonation charts aren't going to work now that you've done this to your beer.

Quote:
My Scottish 80 Shilling finished fermenting 2 weeks ago (confirmed by hydrometer, tasting, and dropped crystal clear). It has been bubbling slowly and steadily since, what I assumed was CO2 degassing.
Why do you assume that?
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Old 07-13-2010, 04:51 PM   #10
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Have you looked to see exactly where the bubbles are coming from? I would be more inclined to think that you are pulling up gases trapped by the yeast cake on the bottom. I don't think you are pulling a strong enough vaccum to degass any liquids that quickly.... Plus very little CO2 (or any other gas) can dissolve in water (or beer) at room temp. If your batch has been sitting in the carboy for a couple of weeks now then I'd say that very little gas is dissolved in there.

I'm a QC scientist by trade and I have to degass mobile phases regularly before using them in analysis. Our house vaccum is fairly strong and I've never seen any gas come rushing out like that. We have to stir whatever liquid we are degassing and then hold it under the vaccum for at least 5 minutes. Interesting for sure, maybe try it again and watch your yeast cake at the bottom?

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