Looking for reading on Diedrich Curve or slow start fast finish style

#1: Post by **Bell1-1010** » July 19th, 2019, 9:18 am

Hi Guys,
this is my first post over here, my apologies if I'm posting in the wrong section:

I have spent the past 2 years of my specialty roasting career following the "RaoR parameters" (always declining RoR

) with more or less satisfying results with a Nordic style approach.

Recently I decided to work with a more, for a lack of knowing a better term, old fashioned coffee roaster. So I could have a chance to learn the basics from some of the industry pioneers.

In this Roastery I have been introduced to what, I discovered here, is referred as Diedrich Curve ( I'm working on a Ghibli 15kg from coffee tech).
I love the results but I would love to know tons more on the theory beyond this style.

Would you know if there is any documentation around?
Book or anything else?
Or Maybe just point me in the right direction?
Thanks

Ps:
Regarding the term RaoR:
I'm fully aware that Scott Rao has not invented or discovered the always declining RoR, but it is safe to assume he's the one that has introduced it to me and to many others. And you got to admit RaoR is pretty cool as a name!!

#2: Post by **crunchybean** » July 19th, 2019, 10:02 am

http://community.ikawacoffee.com/t/frui ... ources/167

#3: Post by **another_jim** » July 19th, 2019, 4:58 pm

Bell1-1010 wrote:And you got to admit RaoR is pretty cool as a name!!

and sigh. To us folks who have been initiated into the mysteries of high school algebra, it's called a convex curve. It is nearly impossible to not have a convex roast profile, so this is one "rule" that is more physics than roasting craft.

Now to something you can control. In roasting articles from the 80s and beyond, the acronyms SSFF (slow start, fast finish) and FSSF (fast start, slow finish) were used to distinguish typical air roasting profiles (highly convex curves) from drum roasting profiles (nearly straight line profiles). These also differed in time, with airroasts taking around 8 to 10 minutes and drum roasts taking 15 to 18. As higher temperature drop ins became usual for drum roasters, the profiles got faster and more convex, closer to the older air roasting profiles. As craft roasters got better prices for their roasts, they could also afford lower charge weights and lower drop in temperatures on roasters, and thereby get faster roasts while maintaining a classic drum SSFF nearly straight line profile.

But this is certain -- a SSFF roast finished in 10 minutes in the middle of the first crack is going to be very aggressive tasting indeed. The total heat the beans see is refelcted in the area under the roast curve. For roasts of the same length and finishing temperature, a very convex FSSF roast will expose the beans to more heat than a nearly straight SSFF roast. So the more convex will also be more developed.

Below are some diagrams for visual reference. They are not actual roasting profiles, just a guide to the curve shapes (I've drawn the SSFF ass a straight line, but its actually slightly conveex in practice).

Notice the extra total heat (area beneath the curve) for the FSSF roast

Notice to have the same area beneath the curves, the FSSF (Sivetz) roast has to be shorter than the SSFF (Diedrichs) roaast.

#4: Post by **Almico** » July 19th, 2019, 6:44 pm

Here is there Deidrich roasting instructions. They begin on page 19.

https://www.diedrichroasters.com/wp-con ... l-2017.pdf

Highlights:
Low air in the beginning.
Dry target = 5 minutes average.
At yellow open air all the way to eject chaff
At cinnamon close air to 50% (340* in 9-11 minutes) fine tune heat.
1C in 11-13 minutes.
Sample frequently until done

July 19th, 2019, 7:34 pm

You might also find this old Roast and Learn thread of interest -- many of us tried to compare a SSFF and a FSSF roast of the same coffee and shared our impressions of the results.

Roast and Learn Together - May 2015

July 22nd, 2019, 3:44 am

Guys thank you very much for you help,
that's a lot of great stuff!

another_jim wrote:In roasting articles from the 80s and beyond

If I was looking for those 80s articles? Any idea where I could find them? Roast Magazine?

cheers..

#7: Post by **another_jim** » July 22nd, 2019, 3:30 pm

These are refereed articles in food science journals. The major ones were collected by R. J. Clarke into two early 90s volumes, which are still in print. A more up to date reference work is Wintgen's Coffee growing and Illy's Espresso Coffee. Sadly, these don't have anything on roasting. The current best academic authority on coffee roasting is Stefan Shenker. You can download his PhD dissertation, and search for his many subsequent publications.

July 24th, 2019, 3:19 am

another_jim wrote: The total heat the beans see is refelcted in the area under the roast curve.

This line has changed my understanding of coffee roasting for ever. It should have been obvious, but somehow, I never realise that. Thank you sir

I will experiment on this and maybe come back with some questions in a few days if that's ok?

I own a copy of illy book (second version) and there is actually a chapter on roasting. (chapter 4)
https://books.google.ie/books?redir_esc ... &q&f=false
Also I'm gonna get my hands on the R. J. Clarke books as soon as possible.

I really appreciate all your help guys!