Ok, so I've had my Huky for a few weeks and have logged about 20 roasts. I feel like I'm getting the hang of it and am starting to hit the roast milestones in a more predictable fashion. My question is what is the goal of delta BT. Are you looking for rapid change during charge followed by slow change to demonstrate roast development? Is the a goal delta BT ramping up to FC, or after FC? On the videos produced by the guys at Mill City, they comment about shooting for a ROR of ~ 15-18 degrees per 30 seconds. Is this what others are going for? Finally, I've added some graphs. As this is new to me, any constructive criticism would be much appreciated.
Thanks.

In Scott Rao's book (which I believe agrees with many other's roasting philosophies) he suggests a steadily declining RoR through the roast. Others suggest targets like:
30F/min during drying, 20F/min during browning, and 10F/min during development.

The dip you see at 1st crack has to do with the water vapors given off at that phase and the natural cooling from that process. Some would suggest bumping the heat just before 1st crack to counter that.

Those look like very dark roasts. There's no real goal with ROR necessarily. Think of it as how fast your roast is accelerating or decelerating like a speedometer. Have you tried dropping at the end of first crack before your ROR increases again? It might be worth a try.

Tonefish wrote:The dip you see at 1st crack has to do with the water vapors given off at that phase and the natural cooling from that process. Some would suggest bumping the heat just before 1st crack to counter that.

Rob Hoos suggested otherwise in a class last year. He said the release of water vapor at 1C creates an anomaly in the reading but BT continues to rise. Thus he recommends against cranking up the power with that changed reading.

On the other hand, I've read that for some coffees like Ethiopian naturals, where you want to develop the coffee but drop it mid 1C, it helps to have enough power going into 1C so temperature climbs at a good pace during that process. Added: I found the article where Christopher Schooley recommends roasting throygh 1C. It's here, scroll down to the roasting part.

On both of the roast profiles posted above I see a flick, where ROR hastens instead of declining starting near the end of 1C. The flick is said to add bitterness, yet taking some coffees into 2C changes unwanted funky flavors into more desirable roasty ones. I was doing a dark roast today of a Mysore Nuggets coffee sourced at Coffee Bean Corral, where I intentionally wanted to take it to the start of 2C. At the end of 1C the roast started to take off. Those are large beans and at this point the roast is exothermic, meaning the chemical changes in the beans are releasing heat. Seeing this happen I turned the gas off and turned the fan way up and moderated the flick, dropping when I saw BT at 437°F. An earlier roast of this same bean with 500 gm charge instead of today's 1 Kg, the flick was minimized by a similar maneuver and the roast came out extraordinarily sweet with little harshness when brewed at 175°F. Here are graphs of those roasts. The first is from December 3, the other is from today, December 13. The graphs don't mark 2C because I'm too busy managing the roaster to indicate its start in the low 430°F range.





To the original question, this is speculation from a non-chemist who used to be a technical writer communicating others' knowledge. I am guessing that as the roast progresses, the chemical changes that result in flavor complexity and muting of raw tastes are newly formed molecules with chemical bonds that you don't want to disturb with increasing temperature. Declining ROR may preserve some of that complexity while developing additional molecules with their own desired flavors. In this sense it would be an increasingly gentle application of energy/heat. Perhaps someone who knows the underlying chemistry can comment on my speculation.

drgary wrote:Rob Hoos suggested otherwise in a class last year. He said the release of water vapor at 1C creates an anomaly in the reading but BT continues to rise. Thus he recommends against cranking up the power with that changed reading.

+1 from Joe Marrocco from every time I roasted with him. Gases coming off the bean create a looser mass, lower temp. Don't crank the heat.

I don't share the opinion Gary has read about goosing the heat on Ethiopian naturals to prevent this though I am willing to play with it in my cellar lab.

Boldjava wrote:I don't share the opinion Gary has read about goosing the heat on Ethiopian naturals to prevent this though I am willing to play with it in my cellar lab.

I got this second hand but it was attributed to Tom Owen at Sweet Maria's. I'll be interested to learn what you find. Added: No, it was Christopher Schooley.

drgary wrote:I got this second hand but it was attributed to Tom Owen at Sweet Maria's. I'll be interested to learn what you find.

Tom's roasting stuff can be pretty odd at times. He has users of the Gene Cafe taking the temp up to 482*
and leaving it there. Good heavens, that is VERY bad advice. I find his greens selection better than his roasting advice.

Gary, from your graphs, especially indicated by the ET RoR, it looks like you've got a heck of a lot of smoothing (or very low sample rate) going on there. I think you may see a different picture if you dial that back a bit.

And I agree that some say to bump heat before 1C and others say not to. I'm not in a camp yet. Thus far I have typically cut heat (or actually increased damper) to lower RoR then ... along with the temporary natural vapor driven reduction. I'll probably try it the other way too. As soon as everyone figures out who is right, we won't have any fun anymore.

Tonefish wrote:Gary, from your graphs, especially indicated by the ET RoR, it looks like you've got a heck of a lot of smoothing (or very low sample rate) going on there. I think you may see a different picture if you dial that back a bit.

I checked and the sampling interval is set at 4 seconds. What is recommended?