Development Time Ratio (DTR) Question

New Bullet roaster here (V2). I’ve discovered from reading the forum that Rao commandment about always declining RoR does not necessarily apply to the bullet to obtain good results. I have seen less information/thoughts/opinions about the development time ratio commandment. When I used the light roast recipe from Aillio for 500 g my roast curve looked very much like a Rao curve. Declining RoR and DTR between 20-25%. Now I’m trying to do a medium/city+ roast (IBTS probe 216-218 degC) and I’m having trouble getting the DTR sub 25%. Do the more experienced roasters here think that it’s important to prevent baking the beans, or does it not apply to the bullet?

I’d also appreciate if anyone has a good medium roast recipe/curve for 500g on a V2 machine to chime in so I can stalk your roasts. I’ve tried looking on the community for roasts, but there are way too many variables and not enough filtering abilities in the search.


As a newbie myself, and having read Rao’s take on DTR, I have now realized that roast level can be based on DTR, delta temperature as well as weight loss percentage. However, any/all of these can be affected by the ror at FC as well as the moisture content of the greens among other factors. So, over the many roasts I have done on the Bullet so far, I am roasting much better coffee now but am yet to hone on a silver bullet for reaching an ideal roast level indicator.

Going by DTR alone does not appear like a foolproof way to measure roast level. I have done 32% DTR and not reached SC due to a low ror at FC and likewise, I have reached SC at less than 30% DTR with a high ror at FC. Going by DTR alone the former was safely in the dark realm which it was actually not while the latter was much darker than medium dark (as per the DTR).

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Well I see from your roast profile you’ve almost got 200 roasts under your belt, so I would say you’re starting to get some experience :slight_smile: . I see you’re mostly doing 1 kg roasts though, so I don’t think I can copy any of your profiles.

Do you notice any of the baked flavors Rao talks about when your DTR goes past 30%?

Not so experienced here, especially not with 500g batches, but FWIW check out p.33 of Coffee Roasting Best Practices. Seems to me Rao interprets DTR as a guideline rather than a rule. Overall, CRBP has been a very useful book!

Hi all!

I’ve found the 20-25% DTR to work perfectly for light roasts - which is what I recall Scott Rao saying was the target for his guidance.

I’ve roasted plenty of times beyond 25% and up to 30% for a solid medium and I haven’t ever noticed baked flavors. For those longer roasts I have started with fairly high preheat temps and kept a steadily declining ROR - trying to not let it bottom out or stall. So following his other two commandments there, just not the 3rd.

I think most of Scott’s guidance is for how to make “exceptional” light roasts.


Thanks for the feedback everyone.

@Matt_M I checked some of your city+ roasts and they look pretty good. Are you using a V2 machine?

With my 1KG batches, by strictly following a declining post FC ROR I have seldom managed to reach SC and at 30% DTR the batch has emerged medium dark at best. When I have gone beyond 30%, the coffee has ended up flat and lifeless. (My initial attempts at roasting dark)

As of now, I follow an increasing ROR a minute after FC and that has helped me salvage the flavour at the cost of a few craters. For my dark roasts, I now aim for a 35-40° delta temp after FC that I manage to attain within 32% DTR. With this regimen, I’m hitting SC consistently and not dragging my roasts for too long. While saying that I also am keep tracking of my Bean and IBTS temp, making sure not to run free beyond 240℃. Quite a bit to keep track of I should say.


Hi - Yup, I have a V2. My Ethiopian natural roasts all have some odd ROR curve to them because I roast those with high heat & kinda blast right into first crack, then kill it right at the end of first crack. I do that because it was the best way I could preserve the acidity & finish with a fairly short (2 min / 20ish%) dev time to keep it light.

The other beans are all washed & the city+ roasts for those follow a fairly steady decline ROR curve. I’ve been super happy with the results.


@cash0612 do you monitor weight loss %? I’ve been trying to correlate weight loss with that “flat and lifeless” flavor. Seems like, depending on the bean, exceeding 14% for light roasts and 16% for dark roasts are signs of trouble. What do you think?

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After reading a post by someone here, I am more conscious now about weight loss. However, since I roast local small farmer coffee (very small lots between 5 to 50KGs of greens from different places and processed in different ways) there are too many variations from bean density to moisture level, bean grade/size to origin to make an objective call based on it. For the same beans, an AA has lost less weight at a similar roast level as an A.

As of now, while recording the details on RT, I do take note of the displayed % weight loss, more as a means to keep track of the greens to roast conversion ratio than a roast level/flavour profile indicator.

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Interesting comments. How about WL% / DTR ?

I personally haven’t had a lot of success with trying to get >20% DTR on light roasts without baking it ( 1 to < 0 deg C ROR during development)
Let’s say 9 min FC at 8-3 deg C ROR with timing for a >20% DTR one would be likely be over 210 deg C and into a medium roast.

Haven’t looked at weight loss divided by DTR. It seems that weight loss can be influenced during the first part of the roast as well as the end. More early power, hence less weight loss, seems to improve flavor in the cup.

Sorry to digress from the DTR topic

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Hi Matt, Would you please share with me your roast profile for Ethiopians Yirgacheffe natural. All my target is to have a LIGHT roast coffee for pour over with clear acidity

Hi! @HadiB

I don’t have a profile for Yirgacheffe specifically. But I have a few other Ethiopian naturals that may be a good starting point:

Each one is slightly different - for example, with the Hambela I ended up using a P1 for 1 minute right at the beginning of the roast because I found too much uneven heating of a City roast. This worked well for the Hambela but wasn’t necessary for the Dambi Uddo or Shakiso.

Let me know if you have any other questions or ideas. Thanks!


Thanks Matt for your kind reply.
It’s crazy I am not able to open your sent roast profiles.

Thanks for sharing. I think we need to obtain a sharable link in the top-right corner in order to share our roast profiles?


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Hi , I would also appreciate a Ethiopian profile for a full city on natural. I have a V1 and roast 500gms each time.