For some of my coffee roasting experiments I wanted a scale I could connect to a PC or Mac. I looked at many scales and the Ohaus Scout® Pro Balance series was a nice blend of capability vs price. This series is designed for educational applications. RS232 (part 71147376) and USB (part 71147377) interfaces are available. This article documents the use of the USB interface. I assume the RS232 is identical as the user manuals appear identical except for how to connect to the computer.
The degassing experiment three was drawing to a close. To recap 100 grams of dark roasted beans were put in one flask, 100 grams of the same beans but ground were put in the other flask. After 24 hours 294 mls of CO2 were released from the ground coffee. Even after 3 days the ground coffee maxed out at 300 mls supporting the literature (1) that ground coffee degasses in 12-24 hours depending on grind.
The whole beans were a different story. The 130 ml of day one grew to 290 mls in nine days. The literature said about 7 days for most degassing. I was getting ready to clean up the experiment when I had an idea. Just for “shits and giggles” why not grind the nine day old beans. They had stopped releasing CO2 but was there any inside that grinding would release? Using the same grinder settings as previous experiments I ground the 100 grams and quickly returned to the flask and stoppered. I was surprised to see gas released with a similar curve to freshly roasted coffee.
In one day 112 mls of CO2 were released. Like fresh roast beans almost all of the release was in the first 24 hours. While only 38% of what a fresh roast grind release, the total release was 406 mls versus 296 for fresh ground.
I have not found any literature on CO2 degassing in older coffee. I am going to continue other degassing experiments to open up the parameters of cause/effect.
My color spectrometer has not arrived yet. Really looking forward to experimenting with it.
Experiment three was a chance to apply all of the lessons learned in measuring CO2 degassing of roasted coffee.
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.
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.
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.
Lesson 5: Track as many variables as possible. By using Artisan I could compare degas roast 2 to degas 3 roast.
Ground ml CO2
Whole ml CO2
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.
In this experiment, I roasted Costa Rica coffee to Full city. I dropped the roast at 450oF. While I normally do not roast so dark, I knew from documentation this would result in more CO2 to be released.
I placed 100 grams of ground coffee in the the left flask, while 100 grams of whole beans were placed in the right flask. I loaded the ground coffee into the flask as quickly as possible, but the degassing speed surprised me. In one hour of capping the flask, 120 ml of CO2 was already released. This is much faster than whole bean degassing. In the previous whole bean experiment with a medium roast and twice the coffee it took 24 hours to release 120 ml.
Another change from the previous setup was to add eye droppers to the end of the tubes. This made it easier to see the bubbles form. Play the video to see how fast the ground coffee released CO2.
Roast profile from the Artisan tracking screen.
This shot image was captured with a Celestron digital microscope. The scale on the right is 1/16″. The beans were ground with a Macap MC4.
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.
My setup is not quite as elegant.
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.
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.
On the commercial coffee LinkedIn group, there was a question on vacuum packing freshly roasted coffee to keep it fresh. When I was at roasting school, we learned how freshly roasted coffee gives off CO2. This is why you need a can or bag with a gas relief valve. Recently, I decided to get a hand vacuum bagging system. It is a low-cost unit available in Canada from Home Hardware for only $20. For a small cost I could experiment with vacuum packing coffee. The bags are reusable but not cheap, at about $1.25 each. As I just want to use the bags for my coffee at home, the price per bag is not a factor. If the coffee was for resale, a much lower cost per bag would be needed.
The Vac N Store kit comes with three bag sizes. My sample roaster does 1/2-pound roasts that fit nicely in the small bag. By sealing the bags, the coffee is not exposed to oxygen, which is what contributes to making coffee stale. What surprised me was how much gas is released by the beans. Here is a bag of just-sealed, freshly roasted coffee. The little hand pump does a fair job of removing air, but is not commercial grade.
Here is the bag 5 days later.
I was surprised how much air was in the bag. This is not from leaking. Here is a large bag of decaf green coffee beans that I packed several weeks ago. The vacuum seal is still tight.
I put the bagged roasted coffee in my grinder this morning, and it was very nice. Did it hold the freshness better? I am not sure. I need to do a side-by-side on the same coffee, one roasted a week ago and stored, the other roasted the day before.
My question coming out of this is how do companies like Illy vacuum pack coffee? I believe theirs stays tightly packed because the coffee is ground. Perhaps on the next roasting batch, I will bag 1/2 as beans and in a second bag, 1/2 ground and see how it compares.