DIY drum roaster - in a HARK gas smoker

[habahabanero]

So - 1st roast: 250g (It can easily tumble 4-500g but a small test first up) The temperature measured by the probe in the centre of the cylinder ramps as expected from my popper experience. Get to 235C at around 12min. I can't hear popping but assume its because of the steel door masking the noise. I open the door, pull the cylinder out and tip the beans into a collander to see they're yellow. How can a probe 1 inch from the beans' surface be reading 235C and the beans be green/yellow/tan.

Why are the beans not heating at the same rate as the air around them? Any thoughts or possible solutions? I'm guessing it has something to do with no fan forced airflow - maybe?

The simple answer to this question is thermal inertia - the beans will eventually catch up with the air temp you're measuring, how quickly they do this depends on rate of heat transfer. Heat is transferred to the beans by conduction, from the drum, and convection - higher airflow will improve convective heat transfer.

Ideally the probe should be in contact with the beans, to measure bean mass temp. I use an IR thermometer to do this, but my roaster is specifically built to enable direct view of the beans. Going from popper to experimental blind roasting is going to require quite a bit of trial and error, but providing you have enough heat you should get there in the end.

I'd love to see some pic's if you can post some.
Good luck.

[Artimus]

I've designed and built an experimental roaster based on things I had lying about. It's based on this HARK GAS SMOKER - Master Butchers Cooperative as a roasing chamber and I built a rotating cylinder with internal paddles from s.steel mesh I had about. I mounted a bbq rotiserie motor to the back of the smoker and the cylinder therefore sits front to back inside the chamber. Using a tip I got from the uglyroaster (thanks), the front axle of the cylinder is hollow (actually a modified kitchen funnel) so a temperature probe can be inserted into the centre of the rotating cylinder for accurate readings and this axle also serves as a bean entry/exit point so I don't have to built doors/hinges into my cylinder design.

I'll post photots if anyone is interested but the point of my question to follow is different.....

I've come from popper roasting, and this was all about more volume for a low budget. I could have gone coretto but had the parts for this design in my shed, and I thought it had merit.

So - 1st roast: 250g (It can easily tumble 4-500g but a small test first up) The temperature measured by the probe in the centre of the cylinder ramps as expected from my popper experience. Get to 235C at around 12min. I can't hear popping but assume its because of the steel door masking the noise. I open the door, pull the cylinder out and tip the beans into a collander to see they're yellow. How can a probe 1 inch from the beans' surface be reading 235C and the beans be green/yellow/tan.

Why are the beans not heating at the same rate as the air around them? Any thoughts or possible solutions? I'm guessing it has something to do with no fan forced airflow - maybe?