Dissolved CO2 and S.G. - Home Brew Forums
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Old 06-28-2013, 12:09 AM   #1
travis0123
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How much does dissolved co2 effect specific gravity readings?



 
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Old 06-28-2013, 12:25 AM   #2
wailingguitar
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I can't speak to the degree of effect, it has been so long since I did side by side comparisons, but there is definitely an effect. When I started working in commercial breweries many moons ago, I was taught that prior to taking a gravity on a fermenting/fermented beer that it was necessary to de-gas the beer. It was demonstrated to me that the beer that had not been degassed would read a lower SG... I had assumed it would be higher, with the bubbles lifting the hydrometer... in actuality it is lower because the beer is less dense with CO2 dissolved in it


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Old 06-28-2013, 01:24 AM   #3
Wynne-R
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Challenge accepted. I have a batch ready to bottle, and I just put out a sample to go flat. Stay Tuned!

 
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Old 06-28-2013, 01:38 AM   #4
wailingguitar
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Quote:
Originally Posted by Wynne-R View Post
Challenge accepted. I have a batch ready to bottle, and I just put out a sample to go flat. Stay Tuned!
Takes a long tine to go flat on it's own... SOP is to vigorously pour the beer back in forth between to containers many times (50 pours was the norm), allowing it to foam up as much as possible and release the gas
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Old 06-28-2013, 02:38 PM   #5
travis0123
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I kinda figured the gas suspended/bonded/? in the liquid would decrease the density/sg, but I just wasn't sure to what extent. I suppose I could measure the sg of my next beer, force carb it, and then measure again. The bubbles acting on or against the hydrometer should stop at some point, giving a better reading. Let me know if anyone tries this or if it makes no sense

 
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Old 06-28-2013, 04:07 PM   #6
Wynne-R
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Mine went from 1.014 to 1.013 overnight (14 hours).

This is not temperature corrected, at a constant 27 C. I used a precision hydrometer that goes from .980 - 1.020. I can read a half point standing on my head and can probably guess pretty accurately within .0002, a fifth of a point.

So, for people who care about precision, I could state it like this:
1.014 .0002 Right out of carboy
1.013 .0002 After two hours, and same reading at 14 hours

I tap the hydrometer before I take the reading, there are no visible bubbles on the hydrometer.

Based on my sample of one, Id say the dissolved CO2 is much less significant than the effect of the out gassing bubbles.

 
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Old 06-29-2013, 12:04 PM   #7
travis0123
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Nice job! Will you do the same with the beer after it's carbed now that you have the base line out of the carboy. This is where there will be a more significant amount of dissol ed co2. The results i think we should see are again a lower sg with carbonation and a rise as it degasses. People are always measuring the sg of bottled beers to try to reverse engineer it for a clone brew. I think the readings are often incorrect because of the co2 content still in the beer.

 
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Old 06-29-2013, 04:34 PM   #8
VladOfTrub
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Flat beer contains co2. Other than in Fred Flinstone Brewing Companies, breweries use a brewers pycnometer with a de-gassing attachment, or the sample is poured through a de-carbonating filter. The test sample is cooled to the calibration temp of the hydrometer......

 
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Old 06-29-2013, 04:43 PM   #9
wailingguitar
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Quote:
Originally Posted by VladOfTrub View Post
Flat beer contains co2. Other than in Fred Flinstone Brewing Companies, breweries use a brewers pycnometer with a de-gassing attachment, or the sample is poured through a de-carbonating filter. The test sample is cooled to the calibration temp of the hydrometer......
Very few use such a device, in all the breweries I have worked for since the late 80s, including some 30k bbl+ regionals, I have never seen one... nor have I ever heard a single colleague mention having one.
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Old 06-29-2013, 04:51 PM   #10
Hex
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I have one and never use it! He must be talking about 'real' breweries like duff inc.



 
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