- January 11, 2019 at 9:31 am #4296Ridge BrannonKeymaster
Hi, I have your 2 lb roaster and roast coffee in a natural gas bbq. At first, I used a variable speed drill as a motor. Initially, I was roasting at 60 RPM – with the correct temp in the bbq spit it took 10 minutes to first crack. Slowing to 30 rpm it took 8 minutes. Then I tried using my rotisserie motor (3rpm) and first crack was at 6 min, 2nd at 11 mins, finished roasting at 13 min. The roast was nice and even. Question – is 3 rpm too slow even though the timing of 1st and 2nd crack was correct? ie was there too much contact with the drum which offsets flavor?
-Ezra RabieJanuary 11, 2019 at 9:32 am #4297Ridge BrannonKeymaster
Ezra. This is perhaps the most fascinating question I’ve heard in a long time. So there are several discussion points here. Let’s talk about rotational speed first. I honestly believe that the slower you turn the drum the longer the coffee is exposed to the flame with every pass. It’s over the fire longer and on the hot metal of the drum longer. This equates to the coffee feeling the intense heat longer at every pass which translates to a faster roast time. Its always been understood generally speaking that 6rpm was the bare minimum give or take about 2rpm for getting a decent roast. This would be less pronounced in a 2lb drum since it’s such a relatively small mass as compared to the larger drums. But dropping into the 1-2rpm range universally it is reported unsatisfactory roasts.
Beyond this, there is the subject of airflow. You may have noticed that some roasters ln, particular of the commercial variety have some mechanism to recirculate hot air through the beans mass while it roasts. This feature has been attempted by a few RK’ers even in the grill by mounting circulating fans to move the air around. This is something that I personally attribute as fun gadgetry and fun experiments but largely useless if you’re spinning the drum between 40-60rpm since its generating a relatively high amount of airflow even without fans, as the coffee spins at 40-60 rpm through the roast chamber. This usually results in a far more even roast and some say that that increased speed translates to a better body in the coffee though I must say my palate isn’t quite so good to tell you for sure. Anything much more than 60 rpm will be excessive causing the coffee to pin to the drum walls from the centrifugal forces. We don’t want that.
Therefore, It is my personal belief that 40-60 rpms generates the best body, and evenly roasted coffee over slower roasted coffee.
What then about your acceptable roast times even though you’re at a slower speed?
It would appear to me that you are setting a temperature and then letting the time go where it goes. You’ll get a relatively good time regardless but I would suggest flipping those variables and adjusting your temperature up and down dynamically to target your prescribed roast time. So you spin for 40-60 rpm and then adjust the heat up to speed up the roast and adjust eat down to slow the roast so that you eventually are able to target the first and second crack times for the volume your roasting. That combination of speed and targeting time is generally the model I always go by and teach and get great results. With that said, I’ve never claimed to have all the answers. You just might have found a better way. If you think so, share your results because you’ll help all of us become better if so. Coffee is subjective. One mans treasure is another man’s dirt and vice versa. Explore and report back!
Shane D. Lewis
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