Posted Wed Mar 2, 2005, 7:52pm Subject: How to Match Profile with Aging iRoast
To date I have roasted almost 5 pounds of SM Monkey Blend for both learning and trying to find a profile for the best roast. Looking back over my notes, the taste of Batch 12 was head and shoulders above the rest, with double the flavor. First to last cup was great; both brewed and espresso. Even good roasts to the same level tasted muted by comparison.
The problem is that I am having trouble duplicating that accidental success, and I can not find the characteristic in the profile that caused it. There are so many small changes to make in the roast profile, what should I try next? How sensitive is quality of roast to small changes in the profile?
The chart below shows the data from the great Batch 12 along with the data from two similar roasts that were OK, but not great. All were done at the same ambient temp; 67F and same line voltage; 119VAC with unit ON, and beans from the same bag with batch size of 120g. The stage profile is; LOW heat (high speed fan) for 4.5 minutes for warm up to about 370F; MEDIUM heat (medium fan) through first crack and slow roast to second crack; HIGH heat (low speed fan) if needed towards the end of roast to bring the beans to 450F in 5 to 6 minutes from start of first crack. First crack is very consistent for these beans at about 400F. Results are a Full City +, maybe a couple snaps into second crack.
I notice from the front panel temperature data that my iRoast is hotter than when it was new. In fact about 15F hotter in MEDIUM heat. This has made it difficult to achieve exactly the same profile, since I have less control to slow the roast below 450F in stage 2. Sometimes the surface bean temperature climbs to over 450F without the need for a stage 3. That is why Batch 15 was a 40second shorter roast than Batch 12. I suppose I could use an extension cord to lower the line voltage a few volts….
I have no way of telling if the aging iRoast effect is caused by the fan slowing down or the coils getting hotter. Has anyone else noticed their iRoast getting hotter with age?
Posted Thu Mar 3, 2005, 5:48am Subject: Re: How to Match Profile with Aging iRoast
You'll get lot's of opinions on this one, but I have concluded that small changes in the time it takes to get to the desired degree of roast has a large influence on the taste. So much so that I frequently do a melange roast where I vary the time to get to "say" full city from 9:30 to 11:00 min on four successive roasts and then blend the beans before using them.
Look to the timing of your best roast as a key to repeating it. (Adjust your program as required to achieve this.)
Posted Thu Mar 3, 2005, 1:08pm Subject: Re: How to Match Profile with Aging iRoast
Bob,
Thanks for the help. Trying 4 roasts at a time is a good idea to test the differences. I have only been doing one or two at a time.
Of course, I was looking for shortcuts. The basic profile above was inspired by the charts you have put on this forum. Thanks again. There are other good hints out there, but they are spread out. Over the last few weeks I re-learned the hard way that Sumatra is really more done than it looks, and that Yemen was into a rolling second crack at 435F; don't know why, smaller bean, different moisture.... It is hard to find a concentrated collection of info that pro roasters may consider their secrets.
Search out another_jim and BobY posts on roasting on this forum. They have published quite a bit of useful information. Your search will lead you to other knowledgable sources az well.
Posted Thu Mar 3, 2005, 9:25pm Subject: Re: How to Match Profile with Aging iRoast
I haven’t noticed and apparent change in the output of the heating element as the roaster has aged. I have noticed differences between identical roasts on the same day about an hour apart. These days I’m seeing as much as a 2-min difference in roast time across 3 roasts. One of the variables seems to be the temperature of the base unit and the roasting chamber at the start of the roast i.e. 70F vs. 50 F. There are many other possible causes for the time differences from roast to roast.
There are so many uncontrollable variables, about all you can do is pick your desired temperature to stop the roast and select a profile that gives you the rate of rise you desire. I think it was Tom of SM’s that said, as little as a 5-degree shift in the final roast temperature can make a major difference in the roast results.
Posted Fri Mar 4, 2005, 5:10am Subject: Re: How to Match Profile with Aging iRoast
So far the roasts have been mixed together for a larger batch. I take a pound to the office each week for drip. I don’t know if I would notice the difference but I’m sure others would.
Posted Sun Mar 6, 2005, 10:54pm Subject: Re: How to Match Profile with Aging iRoast
Here is a chart of 3 new batches of SM Monkey Blend compared with two old ones. The profile was 380F/4.5; 400F/variable; 420F/3. Stage 2 time was 3, 4, 5 minutes for batch 22, 23, 24. I have not done taste tests yet.
Batch 12 and 15 were done before iRoast calibration and show almost a 2 minute difference of time to 450F, even though all conditions were identical.
Batch 22, 23, 24 were done after calibration and the profile changes are clearly visible.
The batch of decaf was included to show consistency with no-chaff beans.
All test conditions were the same except that line voltage was 117VAC for Batch 22, 118VAC for Batch 24 and 119VAC for all others. The profiles of Batch 22 and 24 should have shown a low voltage effect, however the calibrated iRoast automatically compensated.
Batch 12 is the profile I was trying to match. It looks like there is more than one way to get to 450F in 11.5 minutes.
Posted Mon Mar 7, 2005, 8:00pm Subject: Re: How to Match Profile with Aging iRoast
Randy, I read that there is a calibration resistor under a cap in the bottom of the base and thought it would be nice to have the front panel readout match the under pot temps we measure.
So I replace the resistor with a potentiometer and ran a profile with fan on medium speed for 15 minutes, then adjusted the resistance until the front panel temperature reading matched the under pot measured temperature. Thats when something funny happened. I was expecting a more accurate front panel temp and the unit went into closed loop control. You know, like your early model with fan speed that jumps around to control temperature.
Guess they did not change the software, they just mis-calibrated them.
With some more work I discovered their control voltages and learned how to choose one and get some secondary influence on others. My work continues, but from the charts you can see that I have reduced my stage two temperature from 445 degree to 435 and stage 3 temp from 465 to 455. It allows me to stretch time between first and second crack again.
Closed loop control has added benefit of some compensation for ambient conditions. Notice the two volt drop in line voltage caused no change in roast curve of the beans. Also, in test runs, I have covered the cap on the top as tight as I can with tin-foiled covered oven mit (to simulate chaff) and the unit fan speeds up and drops out coil power to lower roast air temp. It's really cool. This is a whole new sandbox to play in. You guys who got the early units were lucky.
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