CO2 capture: track fermentation?

i did some basic calculations today, and found the amount of CO2 produced (per %ethanol per volume of beer).

That got me thinking... couldnt you capture the CO2 from the airlock to track the fermentation process?

Im thinking of building a eudiometer (sp) setup like is used to measure gas volumes in HS chemistry.

There would be roughly 68 gallons of CO2 at atm pressure produced per gallon of beer at 5%vol alcohol.

That may seem like a ton to capture, but given that you would empty it say, 2x a day (less as fermentation continued) a 10 gallon tube could be 6" diameter, and roughly 6' tall.... or a 1' diameter tube that's roughly 1.5 to 2' tall....

This would also be an effective way to capture CO2 for the people who wanted to keg with captured CO2 (another thread... although this seems like excessive work)

Do you think this would be an effective way to measure progress of the fermentation?

You consider this easier than just taking a gravity reading?

possible. the gravity of the wart would affect how much CO2 you got. and you know how much alcohol you can potentially get from a batch. so you should be able to estimate how much CO2 the fermentation should put out.

and putting a hydrometer in the fermenter is really not an option because of the karasen. this seems like alot of work but it should work.

well,i cant take a gravity reading every time i walk by the fermented... im an instant gratification kind of guy....

This sounds like a fun idea, but it doesn't seem entirely practical.

There are a lot of factors to consider that would limit the viable information you could obtain about fermentation (gas solubility in the wort, gas solubility in the solvent you are displacing for the measurement, temperature, effects of dissolved sugars on gas solubility, etc.).

It might be interesting to look at C02 evolution on a small scale at various time points during fermentation and compare that to your hydrometer reading.

i suppose another option could be micro-controlled... if you did time based gas releases, where every say.... 30 min the airlock would be opened and then resealed... you could do a pressure reading before, and calculate how much gas was released each release (from pressurized to roughly atmospheric pressure). given the amount of head-space, the volume could be calculated from that too... this would probably be easier and you could do data tracking of fermentation rate too... might be a bit more error, but less work an floor space than a 10gallon eudiometer....

The traditional airlocks used for brewing do not allow a significant pressure to build up, that's kind of their purpose.

You would need to completely seal the fermenter, thus creating the 5-gal equivalent of a dry ice bomb. :rockin:

You could try looking into flow gauges and some recording device. I've seen flow gauges for CO2 infusion for planted aquariums.

i use corny kegs as fermentors, so they should be sound up to several atm's of pressure, i would also be able to set up the micro controller to release at a pressure limit...

if you think about it, even airlocks add some pressure... i dip a tube into about 6" of water, so theres a decent back-pressure (~0.2atm)... the controller wouldnt be all that much different if you set it to release at 0.5atm gauge....

i dont think they make gas flow meters for the volume flow rates that a home-brew produces... maybe if you were brewing 50 gal instead of 5...

How are you going to compensate for the varying amounts of CO2 absorbed into the wort as the pressure and temperature changes during measurment cycles ?

if the pressure was low... 1/2 atm gauge, i dont think the co2 would be particularly variable in solubility...
The equilibrium reaction for co2 dissolving into water occurs orders of magnitude faster than the co2 leaving water. So as long as i dont have a pressure change large enough to cause bubble to spontaneously form, the co2 should stay where it is while the pressure is released. I think it would be a reasonable assumption for small pressure changes (~1/2 atm) that the dissolved CO2 is steady state and can be neglected from any calculations...

Maybe this is a big assumption, but this should at least give rough data so that estimated mass flow's can be calculated, and thus the speed of fermentation.

Rushis said:

The traditional airlocks used for brewing do not allow a significant pressure to build up, that's kind of their purpose.

You would need to completely seal the fermenter, thus creating the 5-gal equivalent of a dry ice bomb. :rockin:

You could try looking into flow gauges and some recording device. I've seen flow gauges for CO2 infusion for planted aquariums.

Click to expand...

bah, with the standard 3 piece plastic airlock you could modify it with a trip switch so each time the piece in the middle comes down it would get counted. You'd just have to make sure you have a suitable amount of water in the air lock, not too much and not too little.

when You have this number of airlock falls you could either compare it with hydrometer readings, to predict the correlation, or allow some known quantity of C02 to escape through such a setup, and figure what volume based on that.

as for accuracy in measurement of % ethanol, it should provide you with fairly accurate numbers, at least accurate enough to satisfy your curiosity. plus you don't waste any beer/work in the hydrometer flask.

One thing you might try is removing the airlock and replacing it with an empty plastic bag. Secure it with a rubber band. Measure the time required to fill the bag, before it builds any kind of pressure. Divide the bag volume by the time and you've got a CO2 production rate.

I'm curious about this myself. I found this site while searching for the bubble volume of a standard carboy/airlock. I did not find it. I wanted to use the volume to help estimate the fermentation rate.

Cheers