Roasting - Batch to batch equilibrium

Hey guys, I was curious as to the different routines that everyone used for stabilizing roaster temperature.

I feel like it’s generally accepted that you want to run the roaster at temperature for a while when you first start it up in the morning to allow the drum to absorb all of the necessary heat. I know that Rao recommends charging 50 degrees above your intended charge for 20 minutes or so, and then dropping to your desired temperature. This makes sense to me, but I was wondering what routine people instituted in between batches, especially if a change in charge temperature is involved due to roasting a different coffee or batch size. Is there a point of diminishing return where any stability benefits are overshadowed by energy waste by keeping the roaster burning longer?

It’s a bit of experience, a bit of guessing and seeing if your intuition works out.

If I’m roasting batches of the same size all day, I just run air until I get back to my charge temp for that weight and then dump into the roaster. My thinking behind this is that if I warm up in the AM with 50° above (or in my case 40° above) my charge temp, that’s very similar to my finishing temp for most of my roasts. I charge at 370°-400° depending on my batch size. If my batch finishes between first and second crack with good development it’ll be a nice 430-435 when I dump. So that’s pretty similar to where I was idling before 1st batch anyways, so ideally my thermal energy should be pretty similar to where it was when I was idling up there. So, assuming my next batch is the same size, I’ll drop back down to the same charge temp I used for my first batch and dump my coffee in.

As we all know, probes don’t tell the whole story… so I try to never go from a large batch to a smaller batch. I normally try to always go up in size. I think this is a good practice as it helps me estimate my charge temp better throughout the roasting session. As the roaster’s thermal energy gets higher and higher throughout the roasting session, I’m only ever putting in the same size batch or larger batches.

Through experience I can now fairly accurately estimate my charge temp and get with 2-3° of my goal turn temp without much trouble. However, if I dump in a smaller batch halfway through, I’ll generally have a turn temp that is way too high and I’ll be roasting hot the whole time.

I’ve been trying to leave about 10 minutes between roasts to try and let the drum come back down and settle out from the finishing temp, but that make a lot of sense to just think of it as replicating the conditions before the first roast of the day.

That also makes so much sense to work your way up in batch size through the day. I’ve definitely had some issues with runaway roasts on smaller batches before. Time to start planning out my production days a little better…

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