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 How accurate is BT thermocouple and why is 428? the limit?
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| TimPiazza |
Posted on 05/19/2016 1:34 PM
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 Newbie  Posts: 22 Joined: April 24, 2016 |
On my first roast after upgrading to the 2K+, 2nd crack started at 397? according to my BT probe. I carried the roast a 1:27sec past the start of 2nd crack and dropped at 408?. No problems there, but others have suggested 2nd crack typically starts around 428?, the same temp that the HotTop is configured to drop at as a safety measure. My newbie conundrum is this discrepancy. I can accept that BT accuracy is going to be difficult with a small batch on a light roaster, but I wonder why there isn't a way to calibrate this to more closely match actual temperature? Of course, I'm assuming that 428? for 2nd crack is pretty darn close to a universal truth. If it's not, then it still comes back to why is 428? the HotTop upper limit? Why not 448? or 458?? |
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| RobertL |
Posted on 05/20/2016 10:54 AM
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Newbie Posts: 22 Joined: February 16, 2012 |
I don't own a B2K+ but I've noticed temperature differences on other owners profiles in various forums. I think it's due to the probe placement. It's disappointing that Hottop didn't get this right this time. The good news is as long as your temperatures are consistent and repeatable then your good. |
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| TimPiazza |
Posted on 05/26/2016 11:32 PM
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Newbie Posts: 22 Joined: April 24, 2016 |
I wouldn't be so quick to assume HotTop didn't get it right. I previously had a K thermocouple extending about 2" into the bean mass and that was more accurate, but still off by 10?. If I add 35? to my BT readings, then both 1st crack and 2nd crack fall in line with what others say, 395?/430? respectively. It may be that Artisan has a way of tuning the BT value for accuracy. |
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| TimPiazza |
Posted on 05/27/2016 12:13 AM
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Newbie Posts: 22 Joined: April 24, 2016 |
A quick addendum to my accuracy notation. a legacy article on sweetmaria's points out that actual internal bean temperature is around 40? lower than probe readings, which makes sense because no matter what, a bean mass probe is going to be reading the exterior of the beans and inevitably some amount of the environment temperature, so you would expect it to be higher than if you were to stick a probe right inside of a bean. Perhaps the HotTop has adjusted for this variation? I could find nothing in Artisan that enables a calibration of the probe input values. Tim |
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| snwcmpr |
Posted on 05/27/2016 8:30 AM
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 1 1/2 Pounder  Posts: 925 Joined: March 03, 2011 |
If I recall correctly.... the temperature you are reading is a combination of the beans and the wall of the HT. Intentional design, I understand, not an error. If what I have read here is correct, your 10? difference with the 2" probe may be a result of placement, separate from the HT temperature factors. --------------
Backwoods Roaster "I wish I could taste as well as I wish I could roast." As Abraham Lincoln said "Do not trust everything you read on the internet". |
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| Randy G |
Posted on 05/27/2016 9:20 AM
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 1/2 Pounder  Posts: 398 Joined: February 17, 2010 |
You cannot compare temperatures from different brands of roasters and/or different thermocouple types and installations. What you will find with the Hottop is that the event temperatures from batch to batch are very consistent. And the 428 limit? If you are hitting that you likely assassinating your coffee. Not much further than that is on the cusp of ignition and it could get there in a hurry. I usually do a city+ at about 395 or so. Second begins at about 400 or so. I did test the new 428 max temp and it makes quite an oily mess and creates a lot of smoke with 250 grams. How did the coffee taste? I had no desire to find out. I gave the test coffee away. The aroma of the beans was sufficient to want to dispose of the coffee, one way or the other. And the opinion of someone who has never used a Hottop has little value in terms of this discussion. Moving a probe 1/4" in most any small-capacity roaster will make a difference in the readings. The depth of the bean mass in the roaster is what? 2 or 2? inches? The "accuracy" of the data is not very important at all. The repeatability of the data is what you need for consistency. And consistency is way roasting is all about. If you always hit 1st at 368F (+/-1 or 2 degrees) it makes it very easy to control the roaster by predicting coming events. That's the bottom line. |
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| turtle |
Posted on 05/27/2016 5:37 PM
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 1 1/2 Pounder Posts: 652 Joined: November 06, 2013 |
Once again Randy is spot on. roast to roast consistency in temp readings is important. I.E. FC occurs at the same temp with the same bean time after time. It does not matter what temp reading you are getting as long as it is consistent. It is not the actual temp reading that is important, it is the roast temp at that point in development that is important. If you get "your roast" @ 395 degrees this is the magic temperature you shoot for every time. Mick - "Drinking in life one cup at a time"
"I'd rather be roasting coffee" Roaster 1: San Franciscan SF-1 Roaster 2: Hottop B-2K+ Roaster 3: 2 kilo Chinese drum Grinders: Mazzer Major - Forte BG (x3) Pour over: Hario - Bee House - Chemex - Kalita - Bodum Drip: Bunn CWTF15-1 & CW15-TC (commercials) Espresso: Pasquini Livia 90 auto Vacuum: Cona - Bodum Press: Frieling - Bodum Colombia |
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| TimPiazza |
Posted on 05/29/2016 10:58 PM
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Newbie Posts: 22 Joined: April 24, 2016 |
No worries from me on the actual ? that things happen at, I'm just curious about the correlation between HotTop temperature values and numbers that others discuss. True that it does not matter what temp reading you are getting as long as you are consistent on your machine. It's when you try to discuss your temp readings with someone else on another machine that things get complicated. It's like the railroad timetables before they came up with a way to standardize time. Locally, it wasn't a problem. But across the continent, everyone marked the same moment differently. I couldn't be more pleased with my HotTop investment. So far, every single roast has been enjoyable. I probably need to force myself to make some light roasts, just to see what I end up with. |
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| RobertL |
Posted on 05/30/2016 12:37 AM
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Newbie Posts: 22 Joined: February 16, 2012 |
Quote Randy G wrote: And the opinion of someone who has never used a Hottop has little value in terms of this discussion. If you are referring to me then I wasn't clear in my post so let me clarify. I said I didn't own a B2K+, I never said I'd never used a Hottop. I've been roasting on a HT-B2K since 2011. Also if you read my post again you'll see where I said the temp doesn't really matter anyway a long as it's consistent and repeatable. |
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