Rao on the Development Time Ratio

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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Boldjava
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#1: Post by Boldjava »

Scott Rao has a new blog and I thought I would tag it here.

In his initial blog, Rao posits that the best Development Time Ratio is 20-25% of roasts (notable exceptions). He bases this on thousands of cups from some of the best roasters.

DTR is the time from 1st crack to drop as a percentage of total roast time. I use the same ratio for most of my roasts. When I roast a WP for the first time, I always apply this approach, letting the bean determine drop time. Dry or natural coffees are always in the 18-20% DTR.

Your thoughts? http://scottrao.com/blog/development-time-ratio/

PS. Joe Marrocco terms this phase "post first crack" phase in that the coffee is developing throughout a roast.
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keno

#2: Post by keno »

I learned a lot from reading Rao's book and his approach was particularly helpful in learning how to control a few different roasters as I tried to adhere to his principles, but I'm not so sure I agree with him about DTR.

Consider that most of the profiles from the 2016 World Coffee Roasting Championships don't adhere to his 20-25% range and are well under that range.

That the 20-25% guideline works for his palate is great for him, but those who really like light roasted coffees may find themselves with smaller DTRs and those who prefer darker and more full bodied roasts may prefer roasts with a DTR greater than 25%.

As Rao encourages in his blog experiment with this, find out what you like, and then go with it.

Bak Ta Lo

#3: Post by Bak Ta Lo »

After reading about the Rao% here on HB only, and also now that Roastlogger shows the Rao% on the graph, I followed the rule with my last session. 7 150gram batches on the Quest. It was a high grown washed Panama. I think it is some of the best espresso roast I have ever got out of my Quest.

In the past I had had way to small of a % of development time. Maybe 15% max. I was spending too long in the post turn to first crack phase. I'm developing around the same amount of time now, but it is a higher percentage of the overall roast, around 25%

Is this the basic idea of applying the Rao% concept?

(Edit: Just went and read the blog post, very good stuff!)
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Randy G.

#4: Post by Randy G. »

I had read Scott's book and found much of it very useful in improving my roasts. While working in a booth at the SCAA exhibition in Atlanta I got the chance to ask a number of professional roasters about it and their reaction was always a slight roll of the eyes and a bit of a laugh. When asked why many were not impressed by his use of the word "Commandment" in reference to his rules. When I mentioned that, as I recall, Scott called them this because these things worked for him. It was generally agreed upon that it was a good foundation for a starting point and documenting one man's success, generally speaking..

I would add that the Roaster School - Ep #1 - Turning Point and Roaster School - Ep #2 - Drying/Yellowing - make an excellent addendum (at least) to Scott's book as they get into some details which I found easy to understand and quite educational.

I only mention this to illustrate that anyone who has ever roasted coffee probably has some good information or anecdotes to share that could be of value to you. And they stated (in other words) what I have said for some time, "When you stop learning about roasting you should just start buying roasted beans and sell your roasting rig."

EDIT - repaired links
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Boldjava (original poster)
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#5: Post by Boldjava (original poster) »

Randy G. wrote:... "When you stop learning about roasting you should just start buying roasted beans and sell your roasting rig."
Kindred spirits. Mine is, "When I come to the shop, if I don't learn something about coffee in any given day, my boss should fire me."
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SAB

#6: Post by SAB »

Boldjava wrote: In his initial blog, Rao posits that the best Development Time Ratio is 20-25% of roasts (notable exceptions). He bases this on thousands of cups from some of the best roasters.
I made out a table that I use that gives me a quick estimate of where to drop the roast to get to 22.5 % DTR based on the beginning of first crack. I think having that number in mind has helped me save some roast s that might otherwise have been botched. As I have learned a new roaster, I have sometimes come in to FCs with too much or too little momentum. So, I will sometimes change my planned drop temp to reach an appropriate DTR.

Probably the greatest utility of this is if I've gone in to FCs with too little momentum. By stopping the roast at 25-27% DTR, rather than waiting to get to a my higher planned drop temp, I think I've been able to avoid some of the baked flavors that can come along with a stalled roast.

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hankua
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#7: Post by hankua »

Scott's DTR makes sense if one hits all the markers along the way, charge temperature, turning point time/temp, and ramp to first crack. In a commercial setting it probably gives another level of consistency from batch to batch. We're roasting on tiny machines with little mass and beans compared to shop/industrial versions where the opposite is true.

Development time is another area where a lot of people including me though it started at the onset of first crack, we now know it begins a lot earlier. What happens if one uses a very short ramp to 1C, or an extended ramp to 1C? Does that mean the roast should be dropped solely by the DTR?

Here's a blog post by Neal Wilson who is also a contributor here at HB, regarding the subject and his Typica software. I hope he doesn't mind, if so we can delete the link. It presents a different opinion and I'm sure was never intended to start an argument.

https://typica.us/typica/2016/08/13/dev ... rmful.html

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[creative nickname]

#8: Post by [creative nickname] »

I thought Scott's post was very helpful, thanks for linking to it. I agree that naturals often taste best with a slower start and a faster finish than Rao normally suggests. I also think that his clarification that you can get away with lower DTRs in a drum that is charged well below capacity is interesting, and might explain some of the differing experiences people have had regarding this issue.
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N3Roaster

#9: Post by N3Roaster »

Here's a blog post by Neil Wilson who is also a contributor here at HB, regarding the subject and his Typica software. I hope he doesn't mind, if so we can delete the link.
It's always okay to link my stuff, though it would be nice if people started spelling my name correctly :D

The point of that post was more about explaining why this shouldn't be used as a quality assurance metric (tl;dr - it's going to excessively flag in spec [sensory] batches while at the same time being easy to game to avoid flagging out of spec roasts) as many people who manage people who roast coffee seem to want to try. The concept is fine as a starting point, but harmful as a straitjacket.

edtbjon

#10: Post by edtbjon »

hankua wrote:Scott's DTR makes sense if one hits all the markers along the way, charge temperature, turning point time/temp, and ramp to first crack. In a commercial setting it probably gives another level of consistency from batch to batch. We're roasting on tiny machines with little mass and beans compared to shop/industrial versions where the opposite is true.
...

https://typica.us/typica/2016/08/13/dev ... rmful.html
This is very true. Hank has thought me a lot on "charging lower", which actually is quite a challenge on the Huky. But it's also the key to getting a much more controllable roast. I.e a roast where I don't feel like having to just slow down and push the brakes all the time. As always, the proof isn't in the profile, but in the cup and an approach with charging even lower than what Hank recommend a year ago have given me easy to control roasts, easy to tweak roasts and last but not least ... a much better tasting coffee.