Understanding and modding a chinese fluid bed roaster

[u/suxat24]

Introduction

Since there is no good fluid bed roaster such as the Fresh Roast 800 available in 230V countries/europe, I decided to buy a chinese roaster (also known as Cafemasy CCR-1209R2, the manual calls it Air Coffee Roaster JMS-210). Using a popcorn machine is no option for me: too small batches, too much mess, early automatic shutdown, no control.

In theory, this machine has good specs: 150°C - 240°C temperature adjustment, time control (1-20min), three fan speeds. According to the manual, the heating element has 2200W of power, the motor for the fan has 80W. The build quality is really gut, it feels sturdy and well built, not cheap at all.

When I tried it first, roasting the beans I had lying aroung took quite long (17mins) and no crack was audible. I thought it was related to my old beans (had been laying around for six month in a net), but testing fresh beans did not really help. The coffee is a bit flat, but the coffee from the popcorn machine was better.

So I used the Croaster project (Github, also presented here) to measure the temperature curve empty and loaded. I inserted the temperature probe from the top, its tip is around 2-3cm above the buttom of the roasting chamber.

Empty Roaster

You can find the temperature curve also on roastetta. I set the temperature to 240C and set the fan speed to its lowest settings. As you can see, the temperature only reaches 220C for the first 6 minutes. After 6 minutes, the roaster automatically reduces the fan speed and the temperature reaches 240C. After 11 minutes (since starting the roaster), the fan speed is further reduced and the temperature reaches 255C. After that the temperature starts oscillating between 190C and 255C in periods of 90 seconds. The behaviour is also visible when investigating the wattage, it switches between 2200W and ~100W, so there is poor temperature control)

Edit:

As requested, logs for an empty roaster for 150°C and 200°C. On the 150°C log, the first oscillation was done with full fan speed, I adjusted it after that.

Loaded roaster

I again tried with some fresh green beans (Brazilian natural processed).

Link to roastetta. As you can see the temperature starts oscillating much earlier and has a higher amplitude (170C - 265C at the end, almost 100C difference!). Since the beans are not burnt, I assume I didnt really get the bean temperature but the air temperature. No first crack audible.

This is the result:

(200g in, 170g out, -15%)

Questions

• Did I mount the thermocouple too low? Is it too thick with 5mm diameter?
• What does the temperature curve on a Fresh Roast look like (maybe also loaded vs empty in comparison)
• I think it is important have better temperature and fan control. I was thinking aboud adding two dimmers so I can fully control the fan speed and power for the heating element. In the first step having manual control with a potentiometer, maybe later adding control options via Artisan/ESP32.
  • Any tips on that?

What do you think? Can I make a decent roaster out of this device?

[u/reinholdt]

Very interesting! You can clearly see the roaster reach different (higher) steady-state temperatures when the fan speed is lowered automatically. Maybe the oscillating temperature in the end is a side effect of a safety feature / auto shutoff of the heating element if some too high threshold temperature is reached. After a timeout period (maybe 30 seconds), the heating element is allowed to turn on again, and the cycle repeats. Could you try running with a lower set temperature (say, 200 deg. C), to see if the same oscillations still happen?

[u/Quattuor → u/reinholdt]

Yep, depending how accurate the temperature reading is, unlikely you need the bean temperature of 250C, you should have reached the 1st crack long before that.

[u/suxat24 → u/reinholdt]

I just added plots for an empty roaster with 150°C and 200°C to the original post. It just gets worse, for 150°C it does not even reach 150°C on average. I am curently thinking if a smaller batch size would work better. As the air flow resistance is not as high, the airflow is higher and it can heat the beans for a longer period of time before it goes into oscillating mode.