Length of time and how deep (increase in degrees above FC) to go into development

Hey Bullet Community,

I hear a lot about DTR percentages, total time in development, and stretch degrees beyond FC. Often I don’t know if the suggestions I hear from more established roasters can be taken literally since I’m mostly using the IBTS to monitor bean temperature. (Still haven’t figured out how to practically use the IBTS for RoR but that’s another post).

In your collective experience, how do you choose how many degrees deep to go beyond FC? If say FC is 200c, how in general do you see stretch degrees beyond 200 affecting the end experience? Why/when would I choose a drop temp of 202, 210, 220 ? We hear a lot about TIME after FC, but rarely is the discussion how long AND how deep ? How does a 90 second DTR with an end temp of 205 differ from a 90 second/212 drop for example ?

Looking forward to hearing some thoughts on the matter,



Not using DTR to decide the roast degree due to different batch size may end up with different DTR with the same variance of bean…not to mention there are different variance of beans will also influence DTR.

Most of the time, for Bullet, I will use IBTS to monitor the FC since IBTS is very consistent on FC with different size of the same bean. It provides accurate temp of FC and the timing to adjust the power needed in different phases.

As to decision on when to drop the beans after FC…I like to use BT …say FC @200c then +2~3c when BT reached 203, I will then drop the beans.
If someone like me going mostly for an extreme light roast, the power after FC can drop down to P1 and if you still using delta IBTS after the FC, it will sometimes gives - delta or just a minor +0.5c delta. This will make roast degree decision difficult

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Based on my personal observation, given an FC temp, the SC generally takes place around delta temp 25°C. So, a bean with an FC of 200°C will have a SC between 225 - 228°C. Using that as a general guideline, I drop at delta 15°C for light, 20°C for medium, 25°C for medium dark and 30°C for dark - this is given a degree or two here and there.


Thanks for sharing Fred, I completely agree regarding DTR. Altering your Drying/Yellow times will change your DTR percentage even if you stay at a 2 minute DTR for example.

I’m not sure I fully understand though what you mean by the Delta on the IBTS post first crack? Are you referring to the The I-RoR value getting unreliable at such low values post FC that it’s more difficult to accurately predict your stretch development degrees if going for a super short DTR? I have yet to actually use the I-RoR and instead opt for the bean probe RoR in general, but perhaps I’m missing out on a great tool.

Hey Cash, that’s a really helpful guide you laid out there. I’m assuming you’re speaking exclusively about IBTS temps. Interesting to read you go 15 degrees post first crack and still consider it in the light realm. I imagine the trick is to have enough momentum to meet that target within 30-90 seconds post FC correct?

Personally I think the highest I’ve taken the final IBTS drop temp on a roast so far is 212, and that was for a 3 minute development and it was definitely in Medium territory, MAYBE medium light but just eye-balling the beans it was a darker shade. I did notice though that the flavor in the cup was a bit more muted than I would have liked. Tamed acidity, and actually surprisingly lacking in the Milk Chocolaty Guatemalan flavour I was aiming for, almost under-developped in a manner of speaking but not referring to anything grassy or biscuity. Do you think that the tame acidity is because of the 3 minute development (acid being cooked down), and the lacking in chocolaty flavour is because I didn’t get hot enough in that time before dropping to manifest them?

It was IBTS temps that I was referring to. I find IBTS very reliable and consistent. I started off using DTR for roast level but there were so many variables affecting it. As of now, I use drop temp for my roasts. Meanwhile, roast level appears to be very, very subjective. In my side of the world, dark is oily, way past SC. My dark is a few seconds into SC which is quite lighter than what a lot of folks expect. My light, I guess, is a tad darker than yours. I have moved up slightly from 1Kg to 1.05Kgs, so two batches yield a little over 1.5Kgs. I have given up on a decreasing ror curve right through for my dark roasts - the development time extended for way too long. As of now, even for my dark roasts, the development time rarely stretches beyond four minutes.


Hi Jeff,
Sorry the “delta” confused you. I am using final BT temp as the decision to drop the bean. Because IBTS higher sensitivity/quicker response time, during the post FC period IBTS dropping while BT still increasing in most of my roast style. Using BT during post FC with the final BT temp to decide the drop is easier for me to control with enough “delta” (FC BT - Drop BT) to identify what change if needed to make my next batch…hope that helps

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Hi Jeff, Fred, Cash,
I find the development time is the factor that has the most influence on flavour, but IBTS drop temperature above 208C brings some roastiness. My experience is restricted to development time around 1:40; longer than that seems to quickly flatten the flavours, to my taste. Also you can almost dial up the acidity by making that time longer or shorter.
With faster or slower roasts, I end up at the same absolute development time, around 1:40. So I don’t find DTR (%) relevant. I know Scott Rao says DTR is the important factor and best around 20-25% but my roasts end up with development time consistently shorter than that. Maybe these observations are only applicable to the light roasts I do.
With RoR (IBTS RoR) steady decline avoiding big swings seems to give best results, and the BT RoR doesn’t give different information.


It seems we could have a characteristic of development related to post FC time and temps to better communicate and measure.
Perhaps, Development Time Delta (DTD)
One could describe the slope of the ROR (linear regression) post FC [assuming you have a declining ROR] for example (7.3-5.2 ROR / 90 secs). To me this seems much more informative of the post-FC conditions. For example you’d know that (2-1 ROR / 230 seconds) = .0043DTD = Baked with a 203.8 drop temp (given 200FC). Plotting DTDs with time, a chart split to 4 quadrants may suggest Low DTDs are underdeveloped or baked, high DTDs are over developed or ‘scorched’, and perhaps a central range or trend of ideal DTDs exist.

By further exploring the continuum of DTDs and combining that with DTRs, one could better correlate and communicate favorable roasting techniques.

Notably, the post FC trend of ROR would commonly require a polynomial regression with an equation that is much less readable or useful to the typical roaster.

Any other thoughts about describing the ROR trend better?

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Hi ryweller,
You’d need a lot of data with comparable tasting to analyse so many parameters. Does the shape of the curve vary much, for a given development time and drop temp? I can’t imagine having so much control over a roast to shape the curve during development.

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Good…looks like you have find a way…but the only thing is your development time is RoR related…if both roast with 1:40 post FC to drop the bean…where one roast with 5c RoR and the other is 10c RoR. The end temp will be different and the roast degree will be different. That will end up with different taste.

I am on ryweller side. With DTD in mind, in a way, one will have to consider both time and RoR. For sure, I don’t have the capability to use DTD during roasting to make the decision but it is a good way to decide what will be the optimized profile after the roasting…Personally, I would like to use end temp rather than time if I have to make the decision during just 40" or 60" of my final stage. RoR on the bullet fluctuate a lot (unlike Artisan or Cropster) It’s not a stable factor and it differs between batches. And I use BT temp to make that final decision. not IBTS temp.


absolutely, I know what you mean!

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I like that framework. I always consider temp change from FCs to drop in relation to time as they have a definite in-cup relationship.

Going through my logs and doing some simple math I tend to aim for a .10 DTD or less (8C temp delta over ~90 sec).

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I think it probably got it too hot with a 212C drop temp and maybe too flat a ROR resulting in a baked roast. That’ll kill all nuance.

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Hey Brian,

That was definitely the case, I have since roasted the same Guatemalan and dropped at 208 IBTS after 1:40 and there was way more milk chocolate toffee goodness to be had. I am slowly learning that the amount of time spent in DEV, for me, is best between 1:30 and 2:00 minutes, regardless if the bean tastes best between 206 and 212 drop temp. I do want to try and achieve a 215 drop temp in less than 2 minutes and see what experience can be had in the cup.

I’ve been spoiled with amazing light roasts from other roasters over the years and anything above 210 usually tastes dark to me lol.

There’s a ratio/formula describing this that’s been kicked around a bit.

Its the total temp change from 1C to drop divided by that time period. It isn’t definitive though as a stand alone number is incomplete but it is illustrative.

It also is somewhat roast dependent as probe location in the mass effects its results. IE, in my Huky with charges of less than 200 grams all temps are high high high as the bean probe is reading more air and less beans. I’d suspect the same might be said with the Bullet.

Like you, too-high drop temps seem to result in roasts that are overdone for my tastes. Glad you’re finding your sweet spot with that Guat. Sweet milk chocolate toffee coffee is a joy.