Posted Tue Jan 25, 2005, 3:10pm Subject: Modified iRoast Yields Consistent Roast vs. Time Results.
There have been many posts here regarding the difficulty of getting consistent results with the iRoast “as-is” out of the box. I agree. Being new to roasting, I read a lot before purchasing the iRoast and then tried to use the sight, smell and sound method to determine roast level. Even though I knew the roast would develop fast, I was still taken by surprise. The resulting “smoke damage” is fading to a musty incense odor a week after this first naïve attempt. I believe the first crack, second crack, oil and Italian Roast all happened simultaneously between 4.5 and 6 minutes. (150g of SM Monkey Blend; 350 for 3 min, 410 for 3min) Since then I have tried several ways to slow down the roast and get a consistent roast level vs. time; and to some extent they all worked. A chart of iRoast front panel temperatures showed that using less beans helped more than either the “gasket 8 hole rotation” or “coins under the cap” modifications. Yet my roast levels were still inconsistent and disappointing in the cup.
Then I tried a simple modification that has given me relatively consistent time vs. temperature results and totally eliminated thermal runaway. It involves removing the filter screen in the cap. Yes, this does allow some chaff to blow around the room and it was difficult to remove the pressed on heat shield from the cap, but the change is reversible if you wish. The cap screen getting clogged appears to be the major cause of the inconsistent results. Charts of the iRoast front panel temperature from the next 5 roasts with this modification are nearly identical for both high and low chaff beans. One of the five roasts shows some signs that the chaff collector itself is getting full and the temperature climbs about a minute faster, but not at thermal runaway speed. The other 4 roasts have matching temperatures within seconds of each other.
I was concerned about having enough heat to roast with the increased airflow resulting from this modification, but found I was able to achieve a Vienna Roast with a 350/5min and 410/8 min setting. Therefore 13 minutes was the longest time to second crack I was able to get with SM Monkey Blend, resulting in almost 6 minutes from start of first crack to start of second. The line voltage was 123.3VAC with the iRoast OFF, 119.6VAC with it ON. Time to second crack can be shortened to prevent cooked beans by using the third level temperature setting of 470 degree at the time of your choice.
Has anyone else tried this modification? If so, what are your results?
Posted Tue Jan 25, 2005, 5:44pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
I seem to remember someone replacing the screen with one that had a larger hole. Another option would be to remove the entire screen cap unit and replace it with some kind of damper. But from your data it looks like you are where you need to be.
Posted Thu Jan 27, 2005, 6:46pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
Randy, I will try a few roasts with this modification and see how they turn out. A damper sounds like a great way to fine tune the temperature ramp rate. For now, if the batch does not raise to temperature, I will try using an oven mit to cover the cap for the last few seconds. The two batches on the original chart came out as light french and french roast, so I know this unit has the heat. Too dark for my taste.
So far I have tossed more beans than I have brewed. Gave in and got an insertion probe TC. Installed it using the pics from Bob as a guide. What a difference! No more guessing when to push the COOL button. The next two batches roasted to 150dF with a nice brown color. The Donky decaf was slightly darker and entered second crack, the Monkey blend was at a Full City roast. This is a lot more fun when you can drink it. I admire the talent to get a good roast without this instrument.
I include a new chart below to show consistency of roast temperatures between a batch of high chaff Monkey Blend compared to no chaff Donkey Blend. I would expect to see some difference as the batch size gets larger.
My next challenge will be to try and modify the profile and compare taste. The next batch will use your 325/350/370 profile.
What is your line voltage at the input to the iRoast when it is ON?
Posted Thu Jan 27, 2005, 9:05pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
Wow you I-Roast is running hot! I’m surprised you can reach the temperatures you are getting in step 1 and 2 with such low settings and the screen removed. Looking at your results with your profile 4 min @ 325, 5 min @ 390 and 6 min @ 460. I would try to reduce the heat at the middle and the end of the roast. So I would try 4 @325, 5@ 370 and 6 at 390. This will flatten out the curve some and stretch the time between cracks. An external TC is the only way to go. Are you using a stiff of flexible TC?
At my house I have 123vac at the plug and it drops to 119 when the I-Roast is running. I assume with you living in Minneapolis you are roasting indoors. So variation in ambient temperature shouldn’t be an issue.
Posted Fri Jan 28, 2005, 4:05pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
Hairdog, The pics of the temperature probe modification are for a solid insertion probe and can be viewed at topic: iRoast - WoW! My new Probe and Thermometer - what a difference! by author Brokencup. 25Sept2004
Randy, Yes, you are right. I just went back to your 25 Nov 2004 post with chart and noticed that both of your iRoast bases were at about 325dF at 4 minutes. Mine is at about 370dF the same time after start with the same setpoint, about 45dF hotter, and now I know that they were both running at the same line voltage. And that is with the bennefit of increased airflow due to the cap modification; which should lower the cooking air temperature. In reality it should have no effect untill there is chaff present. Obviously these things are different from the factory. I don't know if the extra heat is good or bad. I will do more tests.... For reference, my iRoast serial number is 0490000991
I am using the stiff insertion probe by Fluke, their model number 80PK-22. My probe may be installed higher off the floor of the pot than Bob's; even with the bottom of the center cylindrical barrel. That makes it 3/8 inch away from the barrel, 1/2 inch off the floor of the pot. It is burried within the green bean mass before starting and about half way between the expanded bean mass after first crack.
Three questions Randy;
What is the ambient air temperature when you roast outside?
Does the fan ever change speed when you run your 325/350/370dF profile?
Posted Fri Jan 28, 2005, 11:04pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
daveyjo Said:
Three questions Randy; What is the ambient air temperature when you roast outside? Does the fan ever change speed when you run your 325/350/370dF profile? Where is your TC located in the pot?
The temperature here in Austin in the winter can be anywhere from 28 to 80F. I try to roast when it’s 50 or warmer. The 325/350/370 profile was dialed in when the temp was 70 –80. As the temp outside drops, the roasts get a little longer and/or I will increase the temps 5/10 degrees. I did some roasts on Christmas Eve when it was 35F without making much of a profile change. Needless to say I was having difficulty getting the beans hot enough. Next time I’ll bump the profile 50 degrees and or put the roaster in a box to retain heat.
With my profile the fan stays in fast speed all the time. The newer I-roast bases don’t seem to cycle the fan as the older units did. Any time the program is less than 390 the fan will run in fast. If its 390 or over it will run in slow. The mixing of the beans is very poor in the slow speed so I would prefer to keep the fan in fast. I’m not sure the logic behind the fan speed change. The constant cycling of the fan may have been causing some premature failures. With the fan in fast all the time it is much more difficult to hear the cracks.
My TC is routed into the chamber the same as Bob’s (Brokencup) and is the identical TC and data logger. I use a short length of SS tube to set the depth of the probe. The bottom of the TC is at the same height as the bottom of the glass. It is a little closer to the glass than the center of the chamber. I just widened one of the holes in the cap a little and went straight on into the chamber.
Even with no chaff in the screen the screen its self acts as a restriction to the airflow. More airflow will equate to better bean movement but will cause more heat loss. The S/N on my bast is 049002251.
CoffeeMe Senior Member Joined: 2 Jul 2004 Posts: 102 Location: Singapore Expertise: I love coffee
Espresso: Brewtus II Grinder: Rocky DL Roaster: GeneCafe
Posted Sat Jan 29, 2005, 5:11am Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
Daveyjo,
Diverting from the topic slightly, it's amazing you can hear the end of first crack or even the start of 2nd. I'm having lots of problems distinguishing start and end of cracks... Even using towel on the base won't help dampen the fan noise.
DEchelbarger Senior Member Joined: 12 Feb 2004 Posts: 416 Location: Negaunee, MI Expertise: I live coffee
Espresso: Solis SL-70 Grinder: Macap M 4, Rocky,... Vac Pot: Bodum Santos, Nicro Drip: pour over, Chemex, FR Press,... Roaster: RK Drum, I-roast, manual...
Posted Sat Jan 29, 2005, 7:12am Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
CoffeeMe Said:
Daveyjo,
Diverting from the topic slightly, it's amazing you can hear the end of first crack or even the start of 2nd. I'm having lots of problems distinguishing start and end of cracks... Even using towel on the base won't help dampen the fan noise.
Do you put your ear near the chaff collector? It is tough, but that works for me, it is very easy when you aren't venting it. Even with the vents, I can hear it -- in a way you learn what to listen for.
CoffeeMe Senior Member Joined: 2 Jul 2004 Posts: 102 Location: Singapore Expertise: I love coffee
Espresso: Brewtus II Grinder: Rocky DL Roaster: GeneCafe
Posted Mon Jan 31, 2005, 11:07pm Subject: Re: Modified iRoast Yields Consistent Roast vs. Time Results.
Dave,
I've tried ear near chaff collector, near glass, etc but finding it difficult to detect start & stop of cracks. Rolling cracks are much easier to pick up. Since I'm roasting mainly for espresso, going by sight is the only option. Once it hits 1-2 spots of oil, hit the cool button. But still would like to distinguish start/stop time to further improve my roast. Maybe my unit is super LOUD...
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