Huge rise in ROR everytime I increase airflow

#1: Post by **dannyco** » February 16th, 2020, 11:11 pm

I've been practicing roasting on a new 3kg "commercial" machine I recently got shipped to me from China.
I use artisan to track my roasts and they don't look like your typical roast graphs I've seen online. Everytime I increase my airflow, my RoR increases like crazy. The taste of the coffee is good, but to be honest I'm the greatest coffee taster, I can only tell is burnt or not (anyone want samples in exchange for feedback?).

Can someone let me know if this graph looks good and any pointers you might have.

Thanks!

Also, I'm willing to send out free samples of both my roasted coffee and the green coffee to know if I'm getting a good roast profile. Let me know!

#2: Post by **devlin2427** » February 17th, 2020, 7:16 am

There are many factors at play, but in the beginning, you should find the optimal charge weight and airflow setting, and stick with them for a while.

There's no point in juggling too many variables when you have no idea how they affect the roast.

#3: Post by **Beeroclock** » February 17th, 2020, 7:17 am

I'm guessing your Bean Probe is probably not sitting properly in the bean mass. Also you should check the air adjustment - is it via a damper or actual dial. This is most likely not linear in response. Have you done a lighter test at the trier to mark your weak, middle and high airflow settings?

February 17th, 2020, 7:23 am

What is the airflow control on this machine (Variable speed fan like on an MCR?) Overall your times look within reason. The BT jump is strange. What are you changing airflow from and to at the various change points? What was your batch size? Does this happen on all roasts?

The graph suggests you are introducing a lot of convection heat into the process with the air and I am guessing your batch size may be just covering the BT probe so that when you introduce more air, the BT probe is exposed to the air temp as well as the bean temp. If that is the case, you just need larger batch sizes.

Personally I like Genuine Origin for reasonably priced but decent greens in 65lb boxes. There is a list of vendors here:
Green Coffee Sources List - 2020 What is Wowing You?

Assuming this solves your problem, you may want to skip the DE air change while you are learning. Figure out through batch testing where you get the most convection at a batch size and stick with that until post FC. Easier to reduce variables while you are learning.

#5: Post by **Almico** » February 17th, 2020, 8:43 am

With a drum roaster you have a flame below that heats the drum, but it also heats all the air under and behind the drum. If your air setting is low, there will be excess heat around the drum that will immediately get sucked into the drum when you increase the airflow. That reserve heat will quickly dissipate and, if left on the same air setting, cooler air will start being drawn in and mix with the newly heated air from the burner.

One of the first things you want to learn about your roaster is which air setting allows the maximum heat transfer at your normal heat ramp heat setting. You might be able to figure this out without any beans in the roaster. Start a phantom roast, hit charge and watch your RoR. Play with the air settings and see which setting makes the RoR go up and which makes it go down. You will have to wait 30 seconds in between adjustments to allow air inside the roaster, but outside the drum, purge.

If you have your air setting too high, the ambient air will overwhelm the burner and your heat transfer will actually be less. If the air setting is too low, not enough hot air will be drawn into the drum and the heat transfer will also be less.

Once you find this air setting, just leave it there and control you roast with heat only. Once you get that mastered, then you can start playing with the airflow.

February 17th, 2020, 10:14 am

My Quest M3s does the exact same thing. I finally did the lighter test and found that <3.5 on the dial was basically no air, 3.5 was low. 4 was medium, and 6 was high. Above 6 didn't seem to make a difference. So what I do is start with my fan on 3.5 and make incremental adjustments up to 6 prior to first crack. Usually that means doing 3.5->3.6->3.8->4.0 at end of drying->4.5->5.0->6 at end of yellowing and then leave it there throughout the remainder of the roast. These small adjustments are made at least 30 seconds from each other, and allow me to start with low airflow and increase without causing a crazy RoR spike.
It also helps me keep roasts short while maintaining a nice looking RoR curve. By using what Almico was mentioning, I have reserve heat I can blow in when the RoR starts to sag after the initial RoR peak. Then I cut heat as I continue to increase the fan. This allows me to cut more heat than I used to, which means most of the energy that causes crashes/flicks is gone by the time first crack rolls around.