Roasting dark: 'S' curve vs constant declining RoR? - Page 2

August 9th, 2022, 2:47 pm

N3Roaster wrote:As for the book, it's finished aside from another editing pass, but I'm holding off until Typica 2 is out because some of the material is easier to put into practice with better tools which I want to make sure are freely available.

Great to hear. I had tried Typica in the past, but my laptop back then wasn't up to running PostgreSQL.

#12: Post by **N3Roaster** » August 9th, 2022, 2:54 pm

In 2.0 I'm adding SQLite as a storage option so that should work a lot better for home roasters.

#13: Post by **Almico** » August 11th, 2022, 8:46 pm

drgary wrote:The idea is to preserve flavors and characteristics like sweetness and acidity inside the bean developed earlier while developing the outside of the bean for darker roast flavors, like disillates. Neal says that the rising BT ROR toward the end of the roast cups better in his classes than roasts to the same level with steadily declining BT ROR. We're not talking about a first crack crash that reduces sweetness followed by a flick that creates papery astringency. Consider the BT ROR increase at late stages of a dark roast as not an extreme change. I expect that the optimal curve is tuned by taste and the look of that curve will differ by coffee and the characteristics of your roaster and sensors. Added: I don't think you want to flatten the curve while approaching the end of roast, because that would go against the intention of preserving internal flavors. I would also think that adjustments to achieve increasing ROR would be small.

I wonder if anyone has ever tried to measure this. It should be easy enough. Make two identical roasts, differing only with one roast having a declining RoR and the other where the RoR tips up at the end. Both roasts ending at the same drop temp, but the uptick roast obviously ending a bit sooner. Measure whole bean color as well as ground color of both roasts. If this theory is valid, then the roast where the RoR tips up, theoretically roasting the outside of the bean more than the inside, should have a wider color differential from ground to whole bean.

From my experience, the darker a roast goes, the lower the differential number, to the point of being vitally the same after 10 seconds into 2nd crack. I really doubt you can get the outside of a bean dark enough to produce distillate flavors while leaving the inside light enough to retain acidity and sweetness by only manipulating the very end of a dark roast.

#14: Post by **drgary** » August 11th, 2022, 11:04 pm

Is it a matter of differentially making the outside darker or having a wider mix of desired flavors? My speculation on inside versus outside of the bean may be incorrect. Neal's post that followed mine suggests that he thinks of this differently.

N3Roaster wrote:There's a lot that really just comes down to the specifics of the coffee and your preferences, but in terms of the question of how much you should let rate decline, I would recommend looking at this more from the perspective of how much time do you want to spend prior to first crack, between cracks, and after 2nd crack.

#15: Post by **mkane** » August 12th, 2022, 9:02 am

And I thought the darker you roasted the bigger the difference in color from out to in.

#16: Post by **Almico** » August 12th, 2022, 10:16 am

drgary wrote:Is it a matter of differentially making the outside darker or having a wider mix of desired flavors? My speculation on inside versus outside of the bean may be incorrect. Neal's post that followed mine suggests that he thinks of this differently.

For a wider mix of flavors, it is far easier just to blend. Adding some light-roasted natural Ethiopia to a darker Sumatra is just wonderful. Your palate first gets clobbered with the bold peppery spice notes of the Sumatra, and, as it lingers, the subtler taste of the Ethiopia surprises, kind of like the prize in the bottom of a Cracker Jack box.

mkane wrote:And I thought the darker you roasted the bigger the difference in color from out to in.

Nope. Early on you have water to keep the heat down internally. Once that is gone, heat transfer in undeterred. That is why we start with high heat and gradually turn it down to almost nothing to keep a roast from running away.

#17: Post by **drgary** » August 12th, 2022, 10:50 am

Yes, but we're trying to see what we can achieve with a variation in roasting technique. What if the Sumatra component in the blend you suggest is more flavorful than roasted with a steadily declining BT ROR. Have you tried that and tasted it?

August 12th, 2022, 11:46 am

Only when I made a mistake. Yes, I've tasted it. No, I won't serve or sell it.

#19: Post by **drgary** » August 12th, 2022, 1:12 pm

Did you take your steadily declining BT ROR roast into second crack and compare that with a roast into 2C with a rising BT ROR at the end?

#20: Post by **Milligan** » August 12th, 2022, 4:10 pm

Almico wrote: Nope. Early on you have water to keep the heat down internally. Once that is gone, heat transfer in undeterred. That is why we start with high heat and gradually turn it down to almost nothing to keep a roast from running away.

To add a bit to your response, I believe they call that the evaporation front that travels edge to the core as more water is driven out until the cellulose tissue traps the remaining moisture that is then explosively evaporated during first crack as the structure breaks due to embrittlement. Then you get the release of moisture causing the dip and subsequent rise back to "steady state" ROR.

mkane wrote:And I thought the darker you roasted the bigger the difference in color from out to in.

Here is an excellent graph of the exterior vs interior bean temperature delta compared to roast time and temperature.

The Coffee Roaster's Companion Scott Rao pg20

PS I hope it is okay to share this graph for our educational purposes. If not then I or administration can remove.