Controlling Temperature (Low Voltage Environments)

Controlling Temperature in low voltage environments and some thoughts on dry processed coffees

Just a few thoughts around this area, that may prove useful or not to people with Gene Cafe roasters…oh you do any of this at your own risk!

The max capacity stated in the Handbook of the gene is quite large and I will probably not often roast such large batches…however, for those people with low mains voltage, increasing batch size, may be their only option to bring roast times into an acceptable window (for taste reasons). Now with non chaffy beans no problem, you can keep dialling up that batch size, but with chaffy beans:

230g is the capacity for chaffy (dry processed) beans, I think for 4 main reasons

  • Chaff that burns makes smoke
  • More beans means bigger thermal gradient across roasting chamber and higher temps at inlet, possibly causing chaff to burn and smoke
  • Chaff could potentially block airflow is there are huge amounts of it
  • Chaff could catch fire in roasting chamber

I don't think it's really going to be anything else special about the bean. If your voltage is a little low, I suppose it's worth trying increasing the limit (I use 250g for chaffy, dry processed beans anyway and have not had a problem, but again this might depend on the beans). Of course if the voltage is low the heating element won't be so hot and you MAY be able to use slightly more dry processed beans. Of course you should watch the chamber like a hawk, be ready to lower temperature if need be and you see the roast getting out of hand. Also mains voltage can go up as well as down, rather like shares!

Just one last reminder…..when reducing temperatures, to control roast times/profiles, less is more. You should vary by 3-8C increments at the most. Too large a variation will simply turn the heating element off for so long, that (simplification follows) one end of the roast is getting cold air whilst the other is still releasing heat into the exit temperature sensor!

Also if you want to control a roast, reduce the temperature from the highest point reached, not the highest point set e.g. roaster set to 245, only reached 228 (1st crack came fast), for a 5C reduction you might want to reduce to 223…NOT 235, which of course would achieve nothing.

Highest point reached is also important….not from what's currently shown! e.g roaster set to 240, it reached 240, element switched off and it's now at 235 (because element hasn't switched on again yet) roast needs to be slowed by 5C you DONT knock it down to 230, just because 235 is showing, you knock it down to 235, the highest point reached!

Obvious I know, but worth covering. You may have seen the Gene roasting and it might look easy (but the operator may have had a lot of experience with the Gene and other roasters). It's not hard, but an understanding of the thermal dynamics is essential (luckily they are quite simple).