I've been a lurker for a little while, and finally wanted to get some feedback on my roasts and have some discussion around roasting on a FreshRoast SR800.
I'm running two thermocouples to Artisan and logging those values. Here's a photo of my setup:
I'm getting good BT curves, but some of my roasts are coming out horribly unevenly - all splotchy and mottled. A washed Guatemalan that I had was the worst, but I'm seeing it to a lesser degree in other roasts. Obviously, air flow is the key element to balance - enough for good bean movement, but not so much that you inhibit heat transfer.
Here's an example of that Guatemalan:
I'm also struggling with a smoothly declining Rate of Rise. I tend to get large increases in RoR when I lower the fan setting throughout a roast. That's all based on washed coffees. I have a natural Ethiopian, and while I've only done 3 batches, smoothly controlling RoR has been horribly difficult - much harder than the washed coffees I've roasted.
Here are a few roast curves:
The uneven Guatemala (Proyecto Xinabajul Chalum from Sweet Maria's)
A not too bad Rwanda (Nyamasheke Gitwe from CoffeeShrub / Sweet Maria's)
Two of the three not so great natural Ethiopian batches (Hambela Goro from Sweet Maria's)
I've tried batch sizes from 159g up to 215g. I've settled on the smaller side at 170g (basically, 6 ounces) in an attempt to improve airflow and bean movement at lower fan settings.
I've played around with a few different approaches, but generally I leave the heat at 9 for the entire roast and start with the fan at 9. Then I back down the fan one setting at a time, about every minute or so, until I end up at 6 for a 170g batch. I found that if I stayed at a fan setting of 7, I could get to FC, but the roast would often flat-line.
I was aiming for about 17-19% development time, but found those roasts to be super light and a little under-developed (though, I don't know how accurate any of my numbers are). Now, I'm aiming more for 19-22%. Generally, I'm seeing about a 11-13% drop in weight.
Here are my questions:
- What size batches are you generally using?
- How are you minimizing RoR spikes that result from lowering the fan?
- What, if anything, do you do differently based on processing method (washed, natural, honey, etc.)?
- How short is too short of a roast? How long is too long? Depending on how I was messing with heat and fan settings, I was hitting FC at ~5:00 or 5:30 on some roasts, but can lengthen out to as much as 6:30 or 7:30 before hitting FC on others
- The Delta Span setting in Curvers >> Filters is what controls the time interval for Artisan to calculate RoR / ∆BT, correct?
- And to make sure I understand the math correctly, it's averaging the rate of change over that 15-second span (or whatever Delta Span is set to), or is it simply calculating the delta between the data point at 0 seconds and the data point at 15 seconds? What's the default setting?