Egholm Senior Member Joined: 24 Oct 2007 Posts: 55 Location: Denmark Expertise: I love coffee
Roaster: iRoast2
Posted Wed Feb 13, 2008, 12:15pm Subject: How does the optimal temperature profile look like?
Hello there,
I've got my hands on a thermocouple - for starters just for fun (sanity checking the temperatures). But now it has got me wondering: Everywhere you write "don't stall the roast", "keep the roast moving through the stages", etc. How much should the temperature rise around first crack - is 4-6*F pr. minute too little/much?
Below I've attached a profile for my iR2 with a T-probe inserted from the bottom, and 1 inch from the chamber's edge. Would you characterize this as a steady increasing profile, or what should I aim at?
Posted Wed Feb 13, 2008, 1:38pm Subject: Re: How does the optimal temperature profile look like?
I don't use a IR2 but 4-6*/min rise at 1st is generally a good amount, Any slower and you would risk stalling and dragging out first any faster and you'll tend to run towards 2nd too quickly. Keep charting and cupping to adjust to your liking. farmroast
Egholm Senior Member Joined: 24 Oct 2007 Posts: 55 Location: Denmark Expertise: I love coffee
Roaster: iRoast2
Posted Thu Feb 14, 2008, 4:49am Subject: Re: How does the optimal temperature profile look like?
Farmroast,
farmroast Said:
I don't use a IR2 but 4-6*/min rise at 1st is generally a good amount, Any slower and you would risk stalling and dragging out first any faster and you'll tend to run towards 2nd too quickly. Keep charting and cupping to adjust to your liking.
Posted Thu Feb 14, 2008, 1:36pm Subject: Re: How does the optimal temperature profile look like?
Nice data/chart! A couple things: from your 'setpoint' and 'bean' temp it would appear that the heaters are full on for the entire 12 minutes. (or does the heater cycle on off at any point?) Also, at what point do you reach first crack? Is 12 minutes the end of roast? (...Just curious....)
Egholm Senior Member Joined: 24 Oct 2007 Posts: 55 Location: Denmark Expertise: I love coffee
Roaster: iRoast2
Posted Fri Feb 15, 2008, 2:37am Subject: Re: How does the optimal temperature profile look like?
Hi Frost,
Frost Said:
Nice data/chart! A couple things: from your 'setpoint' and 'bean' temp it would appear that the heaters are full on for the entire 12 minutes. (or does the heater cycle on off at any point?) Also, at what point do you reach first crack? Is 12 minutes the end of roast? (...Just curious....)
No no, the heaters are definitely not full on for entire period - it does indeed run up and down. If you look closely, you can actually see a small increase in gradient when a new step is passed/begun. The profile has been chosen so that the change in gradient is so small as possible. I have some charts where you can really see the steps kick in - but I figured the best profile had a somewhat constant gradient!? First crack was at 8:00/8:30 - although I really have a hard time hearing them with these slow roasting profiles! It was way easier back when I hadn't mod'ed the machine (and first crack was at 4-5 min). And yes, the roast ended at 12:00 - I have stopped charting the cooling cycle (stupid?)...
Maybe one should be more concerned about getting a good tasting cup of coffee and not cool looking graphs !!!
I have not read anything in your post about the coffee ??? Will you arrive at a good cup of coffee when you make the most accepted graph or when the cup taste the best ?
This does not seem clear in your post ? Sounds like your working backwards.
Posted Fri Feb 15, 2008, 7:00am Subject: Re: How does the optimal temperature profile look like?
DarkMajestic Said:
Maybe one should be more concerned about getting a good tasting cup of coffee and not cool looking graphs !!!
I have not read anything in your post about the coffee ??? Will you arrive at a good cup of coffee when you make the most accepted graph or when the cup taste the best ?
This does not seem clear in your post ? Sounds like your working backwards.
I totally disagree. Charting is a great way to learn how beans react during different times of the roasting process. By Egholms charting he was able to ask a very important question that is, what approx. rate of degree rise/min should I generally be looking for at 1st crack. By looking at the chart I was able to see what temp. 1st happened at without it being mentioned. A chart will show how the beans actually reacted to certain levels of heat being applied at different phases of roast development. After the roast is finished one can examine the roast for scorching, colour, evenness of expansion and then look back to see where and how it occurred and adjust. Then one cups the roast to see if it's too bright, too flat, proper desired flavor development etc. and adjust temp and time at appropriate points to improve. All of the best pro. Roasters I've watched roast record/chart their roasts. This is not to say that a more Zen approach to roasting is wrong but more that there are many different ways of achieving success and consistency with roasting. I'd bet in the future Egholm will not only have great looking charts but will also be able to produce great tasting roasts! farmroast
Posted Fri Feb 15, 2008, 11:53am Subject: Re: How does the optimal temperature profile look like?
Egholm Said:
Hi Frost,
No no, the heaters are definitely not full on for entire period - it does indeed run up and down. If you look closely, you can actually see a small increase in gradient when a new step is passed/begun. The profile has been chosen so that the change in gradient is so small as possible. I have some charts where you can really see the steps kick in - but I figured the best profile had a somewhat constant gradient!? First crack was at 8:00/8:30 - although I really have a hard time hearing them with these slow roasting profiles! It was way easier back when I hadn't mod'ed the machine (and first crack was at 4-5 min). And yes, the roast ended at 12:00 - I have stopped charting the cooling cycle (stupid?)...
The data looks Yummy! How is the coffee? How dark is the roast? (410F would be City on my roaster, you must be closer to actual bean temp than me. Looks about 10F difference: first crack at 390F vs. 400F. So likely all my numbers below are off by at least 10deg.... (first disclamer ;^)
The temp ramp looks so smooth! (like you are using a Variac ;^) Is this really an on/off thermostat? I think smooth constant temp change is better than steps or dips.
My thoughts on 'slowing the roast' at this point: (...keep in mind I use a poppery and I promise to update here if I change my mind in the next year...) You are entering the graph at a nice steep rate (...and you mention first crack at 4-5min with your roaster before...!) I keep the heat rate steep(er) right up to around 370F (hmmm, maybe 360 for you) or so, then back off on the slope to 'stretch' the final approach to first crack. One advantage of air roasting is the ability to pump the heat quickly into the beans during this phase. I take full advantage of this, and I have found no real benefit in taking this step longer. (... As long as the beans can keep up and take the heat and are not being scorched or heated unevenly! These things can ruin a roast and are much worse than heating slower here! Allow a margin or ruin a roast to see what your margin is.) With most beans I will reach this 370F point at 5-6 minutes.
Any 'stretching' I do is after I cross that (somewhere around 370F) range. (This phase usually has a sweet/toasty smoke smell.) I think of this as where the 'pre-heat' is done and the full 'roast' development begins. (...I know it's really going before this...) First crack for me is around 400F and at 7-8 minutes. I rarely encounter a bean that wants to be in first crack before 7 minutes. I have to push too hard for that. My total roast time to City+ to Full City range are usually 10-12 minute.
......anyway, this is where to many roasting experiments have brought me so far. Hope it is useful to someone. See if it can put more 'snap' back into your first crack....
Just another note about temperature and how useful it is for roasting and brewing coffee. ( I'm such a proponent of thermometers, I should signature it with every post!)
If everyone with a roasting issue/problem came to this site with this kind of temperature data, it would sure eliminate alot of guessing.
Using a thermometer for roasting is not about being a slave to an absolute 'temperature profile', it is only another point of feedback about the roast progress( I think a most important one though...). To me it is the difference between leading and following the roast (Uh... assuming you can control the heater!) With respect to all the other sensory clues you have about roast development, there is a cause/effect relationship between the temperature/heat the beans are subjected to and the observed (smoke chaff color cracks) results. Knowing the temp (and controlling the temp!) in advance of these effects allows you to control the roast. Simple.
This is how I get consistent excellent professional quality roasts from my lowly Poppery I.
Egholm Senior Member Joined: 24 Oct 2007 Posts: 55 Location: Denmark Expertise: I love coffee
Roaster: iRoast2
Posted Fri Feb 15, 2008, 12:05pm Subject: Re: How does the optimal temperature profile look like?
DarkMajestic Said:
Maybe one should be more concerned about getting a good tasting cup of coffee and not cool looking graphs !!!
I have not read anything in your post about the coffee ??? Will you arrive at a good cup of coffee when you make the most accepted graph or when the cup taste the best ?
This does not seem clear in your post ? Sounds like your working backwards.
DarkMajestic, I agree: The cup is the important thing in this business. But in the search for this cup, I wanna investigate the temperature profile a bit. That must be my best tool to reproduce a perfect cup... Furthermore, and this was where the question was born: I find there is so many parameters in getting a good cup, so if there is a "do this, don't do this" approach to temperature profiles, why not harvest the knowledge from this guide?! Btw. the cup was fantastic - both the Guetemala Antiqua Finca and Kenya AA+ that has been exposed to it :-)
farmroast Said:
I totally disagree. Charting is a great way to learn how beans react during different times of the roasting process. By Egholms charting he was able to ask a very important question that is, what approx. rate of degree rise/min should I generally be looking for at 1st crack. By looking at the chart I was able to see what temp. 1st happened at without it being mentioned. A chart will show how the beans actually reacted to certain levels of heat being applied at different phases of roast development. After the roast is finished one can examine the roast for scorching, colour, evenness of expansion and then look back to see where and how it occurred and adjust. Then one cups the roast to see if it's too bright, too flat, proper desired flavor development etc. and adjust temp and time at appropriate points to improve. All of the best pro. Roasters I've watched roast record/chart their roasts. This is not to say that a more Zen approach to roasting is wrong but more that there are many different ways of achieving success and consistency with roasting. I'd bet in the future Egholm will not only have great looking charts but will also be able to produce great tasting roasts! farmroast
Thanks formroast! Now I have even more reasons to keep charting ;-) Hopefully I will be able to do those things in time - it's a fun sport this coffee roasting!
Egholm Senior Member Joined: 24 Oct 2007 Posts: 55 Location: Denmark Expertise: I love coffee
Roaster: iRoast2
Posted Sat Feb 16, 2008, 12:00am Subject: Re: How does the optimal temperature profile look like?
Frost Said:
The data looks Yummy! How is the coffee? How dark is the roast? (410F would be City on my roaster, you must be closer to actual bean temp than me. Looks about 10F difference: first crack at 390F vs. 400F. So likely all my numbers below are off by at least 10deg.... (first disclamer ;^)
It's a full city, and it's fantastic! Though, I think I'll stop the roast a minute or so earlier next time, to get it a degree brighter - it's almost too fantastic :-)
Frost Said:
The temp ramp looks so smooth! (like you are using a Variac ;^) Is this really an on/off thermostat? I think smooth constant temp change is better than steps or dips.
No, sorry I wasn't clear about that - the iRoast2 has number of heating elements it control, and further it controls the fan speed, as well. So, I guess it can really produce smooth curves...
Frost Said:
My thoughts on 'slowing the roast' at this point: (...keep in mind I use a poppery and I promise to update here if I change my mind in the next year...) You are entering the graph at a nice steep rate (...and you mention first crack at 4-5min with your roaster before...!) I keep the heat rate steep(er) right up to around 370F (hmmm, maybe 360 for you) or so, then back off on the slope to 'stretch' the final approach to first crack. One advantage of air roasting is the ability to pump the heat quickly into the beans during this phase. I take full advantage of this, and I have found no real benefit in taking this step longer. (... As long as the beans can keep up and take the heat and are not being scorched or heated unevenly! These things can ruin a roast and are much worse than heating slower here! Allow a margin or ruin a roast to see what your margin is.) With most beans I will reach this 370F point at 5-6 minutes.
That's kinda like me profile. If I do it any slower, I won't be able to keep the roast within the programmable 15 minutes of the iR2. Further, it can only have five temperature stages in a profile, so if I start lower, I loose control in the upper area (having wasted a stage there).
Frost Said:
Any 'stretching' I do is after I cross that (somewhere around 370F) range. (This phase usually has a sweet/toasty smoke smell.) I think of this as where the 'pre-heat' is done and the full 'roast' development begins. (...I know it's really going before this...) First crack for me is around 400F and at 7-8 minutes. I rarely encounter a bean that wants to be in first crack before 7 minutes. I have to push too hard for that. My total roast time to City+ to Full City range are usually 10-12 minute.
......anyway, this is where to many roasting experiments have brought me so far. Hope it is useful to someone. See if it can put more 'snap' back into your first crack....
I will actually experiment with a little faster start - based on your explanation about air roasters in the above. Maybe I can get my first cracks a little more audible...
Frost Said:
Using a thermometer for roasting is not about being a slave to an absolute 'temperature profile', it is only another point of feedback about the roast progress( I think a most important one though...). To me it is the difference between leading and following the roast (Uh... assuming you can control the heater!) With respect to all the other sensory clues you have about roast development, there is a cause/effect relationship between the temperature/heat the beans are subjected to and the observed (smoke chaff color cracks) results. Knowing the temp (and controlling the temp!) in advance of these effects allows you to control the roast. Simple.
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