Coffee Degassing Experiment 3 – Ground vs Whole Bean

Experiment three was a chance to apply all of the lessons learned in measuring CO2 degassing of roasted coffee.

Degas 3 Setup

Lesson 1: A photo copy stand was used to support the graduated cylinders. Fill the cylinders with water and place upside down in the tank. Lower the photo rack then support the cylinders with square wooden rods, hold with several rubber bands then raise the attached cylinders with the camera holder adjuster.

Eye Droppers on Tubing

Lesson 2: Using eyedroppers is very effective but you have to slightly point them downhill or the air will escape, just slower. The most effective dropper has a turn on the end pointing down. This made it easier to prevent gas escaping and water filling the line. The eye droppers were purchased at Walmart for $2 a pair. Keep the eyedroppers as close to the cylinder bottom without touching. Water pressure becomes a factor if you put them deep in the water.

Flask with Funnel on Scale

Lesson 3: The critical timing is from grinding the coffee, place in the flask, weigh and stopper. By putting a funnel in the flask on the scale ground coffee could be scooped quickly and accurately.

Lesson 4: I wrote a trivial program to log the time vs the readings. This meant recording readings was just typing in the levels. The program tracked the time. For the time value I used a Unix Timestamp, the number of seconds since January 1 1970 00:00:00 GMT. So to calculate offset is simple subtraction from the first reading. The data was then copy/pasted into a spreadsheet for calculations and graphing.

Costa Rica Degas Exp 3 w Degas 2 in Background

Lesson 5: Track as many variables as possible. By using Artisan I could compare degas roast 2 to degas 3 roast.

Hours Ground ml CO2 Whole ml CO2
30 0
0.05 45 0
0.10 58 0
0.12 62 0
0.13 66 0
0.18 75 0
0.20 80 0
0.27 90 0
0.34 100 0
0.44 110 0
0.51 118 0
0.53 120 0
0.65 130 0
0.75 136 0
1.04 154 0
1.17 160 0
1.28 165 0
1.76 183 15
1.94 190 18
3.79 226 37
11.69 270 89
12.12 280 94
22.12 290 124
23.36 290 126
24.04 290 128
24.58 294 130
25.61 296 132
27.25 296 135
35.65 296 145
36.87 296 154
46.35 300 170
47.62 178
48.65 182
50.75 182
59.44 188
60.89 194
72.75 198
85.32 210
91.38 220
100.10 227
108.91 236
111.60 240
114.28 243
117.01 246
120.31 248
155.70 264
157.01 267
166.09 270
Hours vs ml CO2 Ground (Blue) vs Bean (Red)

Conclusion 1: Ground degassing is pretty well complete in this experiment at 12 hours. 280 ml of CO2 released at 12 hours while 300 by 48 hours. After day 3 the whole beans are still degassing but slowing down.

Next experiment is to repeat this setup but with a medium roast (430o drop.) I also ordered a school grade color spectrometer and am investigating roast colour analysis.

Most Important Conclusion: Crawling into the raw science basics of roasting is really fun.

13 thoughts on “Coffee Degassing Experiment 3 – Ground vs Whole Bean”

  1. Hi!

    i was really excited to see the data you had collected and i wanted your input since i am trying to do an experiment that follows your procedure.

    If possible, it would be very beneficial to get your thoughts on the following =):

    1) Since CO2 dissolves in water. So if we were measuring CO2 emission, will some of it not dissolve into the water? And our numbers might be a little off. If that is the case; is there a way for me to account for that? e.g. in literature it states the ground coffee will release CO2 and CO. My experiment is not focused on ‘what’ it releases, just the total amount of gas released upon roast vs ground. If that is the case, how can i account for the gas that perhaps dissolves in the water? Use something other than water? Or maybe any other solution. Would love to hear your thoughts on that.

  2. Salman

    That is an interesting question. I do not believe the amount of CO2 or CO absorbed by the water would be significant but I have not done a literature search either. Using an inverted graduated cylinder for a eudiometer is not a very precise way to measure gas output. The other factor would be the evaporation of water into the gas in the cylinder. The key question is to what accuracy do you want to measure.

  3. Thank you so much for the speedy replies! 🙂

    1) That is a very important point you mentioned which i had not considered, about the evaporation of water into the gas. Do i still have to consider that if water is at room temperature?
    2) Eudiometer so far is the best thing i could find, and your experiment was what sparked my interest in doing research on this. The question of accuracy, is that i am only concerned with ‘gas output vs time (hrs)’. Not too worried about many significant digits. e.g. 22.1, that many sig figs would make me happy. But i am willing to settle for 22 for now.

  4. More so it would make me more comfortable if somehow i could entirely block off any release of gas into the water. Maybe using a type of water that is not very friendly to CO2 dissolving inside it. Just a thought.

    I am open to ideas. Would love your input in this.

    1. Interesting thought. I don’t have any idea but let me think on it. Some inert fluid would be nice.

  5. I wonder if distilled water would work better. I seem to recall impurities in the water aids in CO2 absorption

  6. Ok.
    I will check back again later.
    Thanks for entertaining my questions!

    Lastly i will mention one more idea i had. What about somehow measuring the pressure of water, or weighing it before we allow the gas to escape into it? Dalton’s Law of partial pressures to somehow solve the issue.

    Thanks again =)

  7. I was looking at pressure to compensate for not lowering the tube to the base water level. Any idea how this would work – ie if the column of water is 10cm high above the water the effect on the volume of gas showing.

  8. True.

    It might be a good idea for me to just somehow understand how the CO2 dissolving in water is perhaps an insignificant amount compared to the the total CO2 released.

  9. It should not be an issue, i don’t think (if i understand the question correctly). Because what you are measuring is the distance water level is moving down, as gas is entering the cylinder. What the interest is in is the volume of gas forming. I don’t think it should make a difference to your data.

    In response to: ‘I was looking at pressure to compensate for not lowering the tube to the base water level. Any idea how this would work – ie if the column of water is 10cm high above the water the effect on the volume of gas showing.’

    1. From what I read the volume shown is not correct as the pressure is reduced, thus the gas expanded, from the force of the water in the column above the water line pulls down. I am not sure if the effect is significant or the effect small enough to be part of normal error associated with reading the gas volume.

      1. I believe there is something even more interesting here to see. Following your question, and having validity in the data.

        Have you tested the same coffee (ground), but different masses with the current equipment. Take a look at those results. I wonder if you will be surprised.

        You can feel free to shoot me an e-mail, to continue this conversation. This blog is getting way too big, haha.

        Sorry, could you please reinstate the question, or modify the response “From what I read the volume shown is not correct as the pressure (are we talking about pressure of the gas coming off the coffee, or the pressure of water vapor formation, or something else, or Ptotal?) is reduced, thus the gas expanded, from the force of the water in the column (is this the force of the water at time 0 vs time 20 hrs maybe?) above the water line (which water line?) pulls down (below the level of the water that is in the container vs level of the water in the column?).” with the following info. Thanks

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