Thanks for posting your impressions Chert. This Onyx Gem Guatemala was a great learning experience for me. I'd never had a coffee want to take off during FC as much as this one. I ended up getting a well mannered roast with very low heat levels. I still ended up with mild tipping that showed up slightly in the cup. The sugar-rich surface seems to "burn" and stick to some coffees instead of releasing as chaff. I did not have any tipping with my Ikawa. Funny enough, Hoos just talked about this with his recent publication so that was very timely. I plan to do another roast using his recommendation of higher air flow to see if I can indeed eliminate the tipping. Otherwise, it is a nice coffee with fruity notes. This roast ended up at a 22-23 roast vision so a solid medium-light. It isn't quite there yet, it was tastier though the Ikawa.

As for this specific roast, I handled it as delicately as I could while not stalling. I went in with low heat, lower maximum heat at the turn, and lower air flow to start to build some momentum. Around max ROR, I slowly adjusted air up for the rest of the roast to aid in pulling heat out toward the end. Slow dry, average Maillard, and it still went a bit higher temp than I wanted during FC. The graph has all smoothing disabled. I think for the next roast I'll not reduce air flow at the start and possibly increase it around FC to reduce tipping. I can't reduce heat much more than I did. I went into FC at the lowest possible gas and completely killed gas around 30-45s in.





Chaff that stuck.



What appears to be slight tipping. To put it into perspective, this is the most delicate I've ever been with heat on a coffee before and there are still some roast defects.

pcofftenyo wrote:I've been working through a sack of an Anaerobic Colombian the last couple months.

With this one and most other anaerobics I get more structured clarity with less funky glob when I take it just a touch slower. My max ROR is a little lower after TP resulting in a modestly flatter ROR slope. That allows me to take it a bit longer (10-15 sec) with less temp change than with a natural. Roast is around 9 - 9:30 total, 10C temp change in development.

With that bean, which I assume is high grown like this Guatemalan, you use a bit less heat at end of dry relative to a natural?

My roast did that ET flip under thing that puzzles me so. (The washed Pacamara I roasted this week did not flip throughout the roast but that it another tasty story). I can't inspect my roast of the Esperanza anaerobic for tipping becuase I am drinking the last of it as a chemex. hot cup has nice balance of acidity and sweetness and flavors I'm getting are chocolate, coffee a pleasant bitter finish that I think could be adjusted in future roast for greater fruit expression; something to aim for. / and if i weren't carefully tasting for it I would not probably consider it, but in the cool cup I think is where there be a bit of ferment, not sure about that.

I was able to roast the Onyx Gem Guatemala Anaerobic Natural on the Ikawa to compare the Cormorant roast to. The roast level ended up a 22 Roast vision so they are comparable. However, the Ikawa roast looks lighter on the surface. So that means the Ikawa roast is more uniform throughout than the Cormorant's.





Perhaps it is hard to tell from the pic but the Ikawa looks lighter in person. Again both read the same on Roast Vision.

Taste notes on the Ikawa: Balanced, clean, very low bitterness, some sweetness, slight undefined floral, slightly tart on the finish, flavors of brown sugar and malic acid (green apple without the sweetness). Not a lot of distinct flavor notes in this tasting but still very pleasant.

Taste notes on the Cormorant: Complex (compared to Ikawa roast), slightly more bitter, juicer with a bit less sweetness and no lingering tartness, no floral, flavors of caramel, much more fruit forward (stone fruit perhaps slight cherry), and more body.

Interestingly, I prefer the Cormorant version simply because it has more flavor and complexity. The Ikawa is cleaner but with less flavor. Same roast level, different flavor profile. Not worlds apart but noticeable in the cup. The Cormorant roast has 2 day rest instead of 1 day for the Ikawa. Perhaps I will revisit this after a week. I'd like to take the Ikawa to a lighter roast to see if there is pronounced floral to be found. I will likely shorten Maillard next time.

Caveat: Coming off of a sinus infection so my nose is probably not 100%

Nice! Thanks for sharing. On the Cormorant, was the burner diffuser open or closed? Or are you one of those lunatics that changes it mid roast

I keep it open. I've got enough variables to mess with! I remember a post saying that Rao suggested keeping it open when asked about the Cormorant. I plan to experiment with fully closed at some point.

Funny, I am the one that he told in an exchange that I had with him in an online class where he said to keep it open. Since then I have done some A/B tests and I just seem to like it better closed. Go figure. Then again I don't think he understood that closed means more convective heat because I did not understand the roaster well enough to know that at the time. Considering he is a Loring fan (no pun intentded) I would think he would like more airflow and convective heat with the diffuser closed.

Funny..I'm one of the lunatics and have been roasting for a while exclusively in a blended format: open at first then closed after DE. Mixed results.

I love the concept but found the huge change in inlet air temp too tough to manage without spike and dip in ROR. I have no idea how that impacts taste but don't imagine it is a good thing let alone repeatable. That said, you may have figured out how to spin the gas dial to keep things in line. If so, please share your secrets!

Chert wrote:With that bean, which I assume is high grown like this Guatemalan, you use a bit less heat at end of dry relative to a natural?

I'll have to pull the graphs and check.