Coffee Roasting Varying drum speed during roast
@Markdmclucas
Posted in Coffee Roasting
Varying drum speed during roast
This topic was inspired partially by my own ongoing curiosity and partly by looking at the charts Meg shared via the Blkcity website (they have sample profiles for each offering, which is a really cool idea). Under the notes of one coffee, she suggested increasing drum speed during the roast, which is something I have yet to personally experiment with but have been really intrigued by the idea of. I've varied drum speed based on batch size and even processing method*, but left it static over the course of the roast. To my knowledge, drum speed is a relatively new variable and the conversation around it is still developing.
Has anyone here tried it? If so, what results have you noticed, if any? Mill City folks: I'm asking you guys, too. I've seen how open and encouraging Derek is to experimentation when it comes to roasting.
Two side notes:
1) Meg, I really appreciate how transparent you are about your process. I think some folks on here would agree. I ordered some coffee from you guys today and can't wait to try it.
2) At risk of turning this into a larger discussion, I've found that increasing drum speed for fruit-forward naturals has yielded some positive results. For example, I keep the drum around 50 rpm for a 16lb batch of washed. For a natural batch of the same size, I'll bump it to ~59 rpm, then increase the heat input and airflow overall, relying more heavily on convective heat. My line of thinking is the increased agitation/tumble means less conductive heat. I've worked my way around to figuring this out, and the sort of final word on it for me has been an older natural El Sal that has been really, really difficult since it came in last year. While it's definitely aged and still showing some of the flaws we've experienced since Day 1, it has responded really well to the changes in roast (direct trade + difficulties during export meant the coffee sat in a warehouse in El Sal for a bit too long and it came straight to us from Oakland with no post-shipment cupping. It's been rough).
Hi Mark,
I have a weekly Q & A session with Derek where I bounce questions like this to him and I type up the answers. It's a nice method because it saves him from digging through emails and forums, and in the process I get to learn a bit more. He's out of the office this afternoon but I'll put this one on the list for tomorrow morning and post his feedback here.
Thanks, Lauren. The more I keep digging, the more it seems like a pretty divisive topic. It'd be nice to have some input from folks I know.
OK, reporting back! Derek has experience roasting on two machines that utilized automation and a change in drum speed during the roast was part of the programming (one profile increased by 10rpm at first crack, another would slow down by 10rpm at dry end). Both, he says, make sense in terms of thermodynamics
Increase at first crack: less chance of roast defect due to decreased convective heat, also forces beans out of the drum quickly during drop which affords you more control (think of it like blanching veggies and shocking them in an ice bath).
Decrease at dry end: They found this setting to be better for high grown washed coffees that you may have a hard time getting to take on energy, gives the coffee more of a chance to absorb heat. The profile was intended to make the dry end happen sooner so a faster drum speed to get there was effective.
Derek hasn't compared these changes at the cupping table, but he's planning on a tasting of several roasts with different settings (i.e. fast, medium, slow, start fast then move slower, start slow then move faster, etc) and I will share our tasting notes here in the forum!
Yesss! This is the kind of stuff I was looking for. I'm excited to hear about the results.
Learning new equipment and the pressure that comes with producing while not botching a lot of coffee in said new equipment hasn't afforded me time to experiment with a variable I'm not already familiar with, but as I said: I'm curious. As soon as I feel more comfortable with it overall, I'll do my best to reciprocate and make some (hopefully) worthwhile contributions. Thanks, Lauren.
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