Low ROR reading

I have just got my Bullet and from day 1 a it has had a low ROR reading, It climbs to 150 degrees then starts to drop. On all post with pictures I have seen that most people’s ROR goes up to around 200 before starting to fall. Is this a fault or does something need cleaning.


Probably too much info but…

RoR is derived from Bean Temp data from the roaster and is read using the Y2 axis on the right side of the graph (“Derivative”). It tells you the speed Bean Temp is rising in C°/min and is the ragged looking curve. I’m guessing here, but it seems to range (in this graph) from a high of about 18C°/min at about 2:00 min down to about 8C°/min at about 8:00 min. The curves you see in your graph are very dependent on the batch size vs. your Preheat setting, Drum speed, Power setting and Fan speed… everything can impact the slope of Bean Temp curve (I think I see RoR most influenced in the short term by Drum speed changes during the roast).

I doubt there’s anything wrong with the plot of RoR which is (currently) a calculation based upon Bean Temp, but guessing at the temp at 1C on this chart, it looks like it happened at about 190°C. That seems a little low based on what I expect to see. For the beans I’ve been using I expect 1C to happen at 202°C - 204°C. The difference could possibly be attributed to sensor calibration or (more likely) a difference in how you and I identify the sound of 1C- very difficult to pick out under the best of circumstances (I wait till I’ve heard the 3rd or 4th crack before I mark it in RT).

The main criteria probably should be how your roasts compare with one another over a period of 50 roasts or 100 roasts when looking at 1C or 2C. If the temps your roaster displays are consistent for 1C & 2C, I would think that is the most significant criteria.

As long as the thermocouple inside the Bean Temp probe doesn’t lose firm contact with its surrounding metal jacket (the “probe” you see mounted inside the front plate) and that jacket is cleaned regularly, that sensor should be very reliable and repeatable. Thermocouples have been around for about 200 years and are generally well understood.


1 Like

Cheers Bruce, thanks for your time explaining in. It all makes a bit more sense.

Well, thank you, but after I re-read my reply I wasn’t sure that would be possible! :slight_smile:


if you change your patch size from 270g to 800g ,the cruve of ror will became smooth,When most of the space in the drum is filled with coffee beans, the temperature detector will obtain a relatively more average reading. When there are too few coffee beans, the detected ror will be affected by the fluctuation of the ambient temperature.