Coffee Troupe

Roasted by Rich Helms

Measuring Roasted Coffee CO2 Degassing

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Posted by Rich on November 24, 2011 at 7:36 pm

As I read more and more on how CO2 is released from freshly roasted coffee I decided to try my own experiment. Basically the experiment is to measure the captured CO2 as it is released. A basic experimental approach is to use an eudiometer.

Eudiometer as shown in Wikipedia

My setup is not quite as elegant.

First Degas Measurement Experiment Setup

The purpose of this test is to try the setup. The flask is 500 ml with 211 grams (~7.4 oz.) of medium roast Costa Rica coffee. The beans were loaded 5 minutes after dump with a temperature of 94oF. The graduated cylinder is 250ml and the tubing 1/4″ OD flexible copper. I am concerned that the inside diameter is large enough that air will escape up and water flow down. I will add a water dropper on the next version to keep water from going in and the air bubbling out. Also the tube should be shorter so that it is easier to get into the graduated cylinder.

12 hours into degassing

Hours ml CO2
1.4 20
3.7 29
11.7 76
13.0 80
19.0 100
22.0 112
24.0 122
24.6 124
26.0 129
36.0 152
37.0 154
46.5 172
48.0 176
49.5 180
59.5 194
61.0 200
71.0 214
84.0 224
94.5 236
104.3 246
108.0 250

ml CO2 Released vs Hours

The papers I found said the degassing would continue on whole beans for 7 days. Now that the output reached 250 ml, the capacity of the graduated cylinder, I am going to end this experiment and set up one comparing whole bean and ground coffee. To avoid the 250ml capacity I will put in 100 grams of coffee.

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  • On February 20, 2013 at 2:41 am Divine said


    I think you are a genius to customized this practical degas equipment.



  • On August 19, 2014 at 2:36 pm Jon said

    Thanks for conducting this experiment and sharing the results. Should you do anything to take into account the solubility of CO2 in water? I haven’t studied chemistry since grade school, but I recall that CO2 has a relatively high solubility in water. From the web (e.g. it looks like water can hold around 1.5 to 1.7 grams of CO2 per kg, at room temperature and pressure. It’s possible that you are losing some proportion of the collected gas by it being dissolved into the water in the collection cylinder and then released as gas again into the atmosphere via the air above the water bath. If there is indeed such loss, things that could help reduce or eliminate it include: putting the water-containing part of the apparatus in a closed container (to make the experiment a closed system w.r.t. CO2 gas); eliminating air from within the closed system (I think); and using a liquid other than water, in which CO2 is less soluble. Is it less soluble in cooking oils, for example? How about just a barrier of such a liquid, at the top of the water column within the cylinder? (Assuming it floats on water.) Anyway, you have at least established a lower bound for the amount of CO2 released over time. Great stuff!

  • On August 19, 2014 at 2:51 pm RichHelms said


    CO2 absorption didn’t seem to be much of a factor as the pure CO2 in the cylinder did not vary with time (ie it did not reduce in amount.) I suspect the potential amount of CO2 absorbed is small in comparison to the amount released.

    The other possibility would be to use some fluid that does not absorb CO2 but this is in my house so it has to be something that is not dangerous or flammable.

  • On September 13, 2014 at 11:02 pm Bill said

    A great little research project.
    Thanks for sharing from all of us at Bills Beans and The SanFranciscan Roaster crew

  • On February 20, 2018 at 10:24 pm Rich said

    From Coffee Guy

    How did you determine the composition of the gas that you collected, or did you just assume that it was carbon dioxide?

    Rich Helms

    I just assumed it was CO2. There is plenty of literature out there to explain why it is CO2. My work was just looking into degas rates.