Anyone have an IBTS drop temp chart for roast levels from city to full city+?
Here’s something from Sweet Maria’s that I found to be pretty close to what I see on IBTS with 450-550 gm batch sizes even though it’s created from thermocouple data. I recently tried an 800 gm batch and a 1 kg batch- at these batch sizes the correlation was not there so tread carefully.
Bruce
Edit- I just reviewed the 0.8 & 1.0 kg roasts and now realize that IBTS data does correlate across all batch sizes I’ve tried. What is different is that at both these larger batch sizes Bean Temp is higher than what I expect to see at my usual 550 gm batch… BT is very close to IBTS at the end of the roast with 1 kg batch.
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So, to get to FC+. you are dropping at 454F on the IBTS? That sounds awfully high to me.
It is awfully high. So I have had to drop at 441-442°F for FC+. 454°F is more like Vienna as I see a lot of oily spots. I started out treating the SM article as gospel then adjusted to my own set of standards.
The issue is the subjective nature of C/C+/FC/FC+… etc. When I was given a link to Roast Vision I finally saw a decent way to get an objective measure of roast color. Unfortunately the measurement is post-roast. But at least I now have a way to confirm some of the temps I use for dropping the beans. The scales don’t match so I had to adapt for my own use.
And I’m finding there are additional considerations that affect the roast color such as the batch size and the rate at which you approach the target temp. So it’s a work in progress.
Bruce
Hi Bruce,
Are you still using the Roast Vision device?
Is it something that you would reccomend?
I find your last statement interesting where you mention “the rate at which you apporach the target temp” . I have been curious about this for some time. Part of my post roast procedure is to break open several roasted beans and look at the color to make sure that the internal color of the bean is as close as possible to the outside of the seed.
Yes, I still use the RoastVision colorimeter (probably measures grey scale vs. color). Works great for my purposes and has been rock solid. Before I was pointed toward the RoastVision I was faced with my subjective impression of the color of what I had just roasted and I was inconsistent at best. That’s been eliminated.
RoastVision uses the USB port on the laptop for power but has no other functionality. That led to an issue where RT3 would close if I disconnected the RoastVision USB cable. That has been corrected.
There are alternatives to the RoastVision and they are all $$$.
There can be an issue with blends especially if they include robusta. A roasted pre-blend can have a range of color as some beans will have a different end-color than others for the same drop temp. The best you can do is to grind some of the roasted beans and stir the grinds before measuring. Single origin roasts shouldn’t be an issue except possibly in the lightest roasts. I’ve found the readings from RoastVision are very consistent. For a given variety, if I roast to the same drop temp I know exactly what the reading will be. If it’s different than I expect it’s because I was off on the drop temp or the IBTS sensor is dirty.
Chaff can be an issue because it doesn’t darken the same as the bean. So I put a little extra work into getting rid of the chaff as best I can.
Bruce
Edit- after I wrote the post above I read in NY Times that, thanks to crop failures with arabica varietals we will probably see more and more robusta in the coming year(s). Probably not among roasters here so I assume (?) it refers to consumer pre-roasted buying options.
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Thanks Bruce.
I ordered one today. They are having a $50.00 off sale until the end of the month. (ends today)
Another update re: RoastVision… I mentioned roasting to 454°F and calling it FC+ in a post above (Dec 2020). The RoastVision has its own scale which runs like this-
There’s no specific correlation between the usual reference to C(ity)/C+/F(ull)C/FC+/V(ienna)/FR (French Roast) so you have to provide your own equivalence. My favorite roast drops at 449°F which is Dark on the RoastVision scale (6-9). Using info from Sweet Maria’s, FC+ drops during the first few snaps of 2C which can be as high as 454°F. My roast drops at about 20-30 sec into 2C or about 20 sec longer than FC+. So there’s some correlation issues with the temp data gathered by Thompson Owen of Sweet Maria’s in his paper on temps vs. color vs. sound and what I see using the Bullet’s IBTS.
I’ve come to accept that I’ll use the RoastVision scale above and (kinda’) ignore the C/C+/… scale. My roasts include color info in the title- usually “Dk” or Dark on the RoastVision scale. “Dark” happens to appear in the Rating info for Roast Comments in RT3. I’m not sure the notation was originally intended for that RoastVision value for color but it works for me!
Bruce
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I’m sure mine works better since I paid $50 more! 
Good job shopping!
Bruce
LOL,
(I found that Espresso Vision has offered the $50 off Code a few times over the past couple of years on their FaceBook page)
I have also been using Espresso Vision for several months now and prior to that I labeled my roasts using a combination of data, time after 1C and ending temp, plus visual inspection through the window prior to dumping. Now with this little jewel of a device I am able set a standard of roast levels indicating the digital read out on the Roast Vision Scale that Bruce provided. One point of caution though, if you are setting up a standard to follow from batch to batch make sure you grind the roasted beans the same each time. Different grind settings will change the color read out of the roasted beans even though they are from the same batch.
Larry
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Thanks Larry,
It is probably overkill, but I ordered a 20 mesh and 30 mesh sieve from Amazon. That should help keep me in the range for SCA cupping protocols and help keep the clumping down.
“If something is worth doing, it is worth overdoing” 
Another thing that I wonder about is: Are people removing the obviously different colored beans after roasting? I have seen machines that the professional roasters use that automatically sort the roasted beans by color and remove any that aren’t in the color range programmed into their machines. The dry process Ethiopian beans seem to have a lot of color variation after roasting. ( “Oh look, another rabbit hole” LOL)
The ones that turn yellow but not brown? Definitely. Those are “quakers” and they taste horrible. 
After each roast I routinely do a scan for quakers & defects which eliminates the outliers that are hugely different (and the occasional rock), but I’m not rigorous.
Chaff is the biggest issue and I deal with that by shaking & swirling the beans in the cooling bowl a lot before winnowing the roasted beans.
Beyond that the only thing I do is stir the sample of ground coffee before measuring with the RoastVision- trying to blend the variations in color as best I can. My dark roasts have a range of 7-9 and it’s repeatable from roast to roast.
Something that may not be apparent is that, since RoastVision requires a ground sample for measuring, you are measuring color from both the outside of the roasted beans as well as the inside of those beans.
Single origin roasts haven’t been an issue for me. It’s a blend that can have a spread in measured values especially if it contains robusta.
Bruce
Edit- if an outlier in color (a quaker) is really light it can be because one or more greens didn’t drop from the chute when you charged the roast, then dropped into the drum late in the roast and aren’t properly roasted. Pays to give a quick look after charging.
Thanks Bruce,
I learned to slowly charge the drum and always check for beans sitting on the little bar.
That is also why I painted the Trier half blue so that I can see that the cup in the trier is facing down. A “friend” told me that he got caught a coulple of times with the cup facing up and ended up with some hard, under roasted beans in the final drop. (okay, it was me…)
I understand about quakers and check for them.
My preference these days are Ethiopian natural process beans and when I see “Heirloom varietal”, I pay closer attention. Also: when I see “heirloom varietals”, I assume it is like a pre-roast blend and the beans may not roast at the same rate and roast to the same color. It is the same thing with first crack outliers. Sometimes the first ones will start cracking at 386 F. I usually mark 1C at 393F. That is usually where the rolling crack is just getting underway.
On wet process beans from Central and South America, the first crack and color is much more consistent.
I haven’t been worrying too much about the chaff. but I did buy some 20 mesh stainless screen from Aamazon and cut it to fit in front of the cooling filter. It seems to be catching most of the chaff that normally passes through and makes a mess behind the Bullet. It doesn’t help with the removal of chaff from the final product.
I expect that I won’t have to change that filter as often. I have a small shop vac set up and vacuum up the chaff.
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That’s a good idea! (in ref to last pic) I have left over window screen I will cut
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