Bean Temp vs Drum Temp during Preheat

Is it normal for bean temp to rise faster than drum temp during preheat? If so, is the selected preheat temp drum or bean temp?

The preheat temp is always the drum temp. You will see that when the red curve (drum temp) starts to flatten out at the preheat temp.
You ask to the speed of the two temp rise? Can you elaborate? The final drum temp is typically higher that the bean temp - but the delta depends on the level of the preheat temp.

My bullet is currently showing a higher bean temp during preheat. The difference is around 50 deg C. I believe the IR sensor is not functioning properly even after cleaning the glass.

Yeah, it seems that either the IR sensor is faulty or still needs to be cleaned - even behind the round IR glass there is the naked sensor that can be cleaned if you really roast deep into 2nd crack often.

Btw, if you pre-heat to like 200-205C the the bean temp will end up higher than the drum temp. Reason is that the measured drum temp is on the inside of the drum - the outside (close to the insulation) can be much higher and this air will be pulled into the drum and measured by the bean temp probe at high pre-heat settings…

Has this problem been correct? If so, how did you correct?

My Bullet R1 is doing this. I am preheating to 190 C and I am getting around 200 C been temp and only 160 C drum temp. When I tried to roast, it did not go very well. Everything was fast and at 189 C I hit beginning of 2nd crack when this is when I would normally begin to hit 1st crack.

I dont know if I should take the actual sensor glass off and q tip inside or how better to diagnose the problem.

Any guidance would be appreciated.


You need to contact Support for some guidance. I think this is possibly an issue with a dirty IR sensor (IBTS). When the sensor gets dirty it reads a lower temperature than is actually present. And, since the IR sensor is used to set Drum Temp during Preheat, that means the drum is hotter than you think it is when the Bullet f/w says it’s time to Charge. In the extreme case Bean Temp can have higher readings than Drum Temp and that’s generally not possible, especially after about 2 minutes into the roast.

If I’m right, you’ll have to do some maintenance by removing the front plate (which needs to be supported during cleaning), clean the roasting residue from the inside of the plate, then use a cotton swab with alcohol to clean the IR sensor inside the black silicone view port. You need to keep track of the screws and the shims on the shaft of the drum (they look like thin washers; there were 3 of them when I received my Bullet).

Here are a few photos of the sensor as seen using a fiber optic camera. The lens usually looks about the same before and after cleaning yet there has always been a difference in the Drum Temp vs. Bean Temp.


Pretty sure this is in reference to a V1 Bullet, so there is no IBTS. It has the original IR drum sensor, which has the (germanium??) glass that needs to be cleaned regularly.

To the original poster and anyone with the same issue…you need to clean the glass before it becomes an issue.

Mmm… he says R1, not V1, but this is a 2 year old V1 thread and he refers to the sensor glass. So it appears I’m full of the wrong info. Mea culpa!