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Homeroasters - Home Roasting Coffee Community » THE ART OF ROASTING COFFEE » Roasting Coffee

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Page 2 of 2: 12

Convection, Conduction, Radiation - Heat Transfer Ratios!
dBndbit	#26 Posted on 09/06/2009 7:48 PM
1/2 Pounder Posts: 268 Joined: January 13, 2007	Stuart, Don't trust me! I'm just an amateur who reads a lot. I have zero experience with professional roasting machines. My background is electronics. Why do people assume that IR absorption depends on color or darkness in visible light? Visible light is a tiny band of frequencies covering just a 2:1 range of wavelength. IR covers more than a 100:1 range. The coffee bean may look completely different across that wide spectrum. I gotta say that when somebody from Ambex says: "You can neither measure [IR] nor control it..." and "The rate and ratio of radiation in a roaster is an unknown", I have to suspect the person just doesn't know the answers and is trying to make me concentrate on something else: using his machines rather than understanding them. In fairness I'm sure that engineering details were beyond the purpose of the document. I have no doubt that Ambex roasters are fine machines, but those comments are very unsatisfying. IR can certainly be measured and controlled by design, if not by the knobs and levers on an Ambex. In the past I once purchased and use some very fine lab equipment for measuring IR. But for some reason when I retired they wouldn't let me keep any of them. I wonder why I couldn't make my own sensor from a set of filtered IR photodiodes from Digikey. Sensitivity could be crude and I could probably work up my own calibrator with a piece of metal of known emissivity and a temperature probe. I need to think about this more. You are asking the right questions. Don't stop just because the answers (or people who already know the answers) are hard to find. Jim 11 years old... forever! ReeferDoor.com >home-built roasters and fair trade
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seedlings	#27 Posted on 09/06/2009 8:22 PM
1 1/2 Pounder Posts: 4226 Joined: June 27, 2007	Quote stuartgrant wrote: Hey Chad - just a quick one. Can you provide a link to the ducted-HG roaster you mention? I've done a fairly comprehensive search of this forum but couldn't find anything... what can you tell me? It sounds great! Cheers Stu. Sorry, Stu, but it's imaginary. I can imagine pictures of glorius wonders, but get bogged down in reality. You should be able to make something like that. Bigger tube, smaller tubes...? Oh, and great links, Marshall CHAD Edited by seedlings on 09/06/2009 8:26 PM Roaster: CoffeeAir II 2# DIY air roaster Grinder: Vintage Grindmaster 500 Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover


stuartgrant	#28 Posted on 09/07/2009 7:04 AM
Newbie Posts: 36 Joined: September 01, 2009	Hi all, #Marshall - thanks for those links. The Ambex roasters article (The Heat is On) was one of the main triggers in getting me thinking about these issues. Great read. The other link was also a good read. #Jim - you're humble, too?? ;) Thanks for the opinion on the article's failure to address IR heat transfer. If I were to hypothesise why that's the case, I guess it would be one or both of: 1) total radiated heat transfer is too hard to measure (for the reasons you stated), and/or, 2) they consider it too low a proportion of the total heat transfer to bother measuring properly... Not sure which! #Chad - aah, imaginary. Oh well; you're right about the general principle being fairly easy to replicate. What about a stirring paddle with jets of hot air streaming out of it as it spins?? Ok, that would be a nightmare to pull off! Someone posted today on Coffeesnobs about an experiment they tried with their Corretto where they managed to get to FC in 5-6 minutes by starting the roast with just the BM element (to 50C/122F), then with the HG on low (for another minute), before proceeding as normal (HG on high etc...). They managed to avoid any tipping by doing this. There's no way our HG-only Corretto could do that without tipping. In any case, I'd prefer to reach FC around 10-12min, but the principle is very useful! I think it (anecdotally) suggests that using a non-convective heat source (or by limiting air flow) at the beginning of the roast, the beans have a chance to dry out more evenly and are less prone to tipping later on. I think this is what happens in a drum roaster; most of the conductive heat transfer happens fairly quickly at the beginning of the roast - and the convective heating takes over from the point of equilibrium onwards. Hot air (especially early in the roast) would tend to dry out the tips, leaving them prone to tipping. That's my theory. How does that sound? Cheers Stuart. Edited by stuartgrant on 09/07/2009 7:05 AM
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Koffee Kosmo	#29 Posted on 09/07/2009 8:19 AM
Administrator Posts: 1620 Joined: December 31, 2008	I have found that everything works at its peak on a sweet spot With a car its a certain RPM Its my belief that roasters work the same way as our bodies do Lungs to fan and stoke the fire Stomach to roast and change a chemical state Intestines to remove the chaff So The sum of all working parts must work in harmony for best results Did I just come up with a quotable quote B) KK I home roast and I like it. Designer of the KKTO Roaster Build information https://homeroast...ad_id=1142 https://docs.goog...lide=id.i0 Blog - http://koffeekosm...gspot.com/ Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex, (KKTO) Turbo Oven Home Roaster.
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stuartgrant	#30 Posted on 09/10/2009 11:08 AM
Newbie Posts: 36 Joined: September 01, 2009	Hey KK, Yeah, I'd say that was quotable. ;) There are so many factors involved: - amount of heat - type of heat - directionality of heat - air flow - thermal mass of roaster itself - volume of roasting chamber So you're right - it's always going to be a matter of balancing these things in a design. --- Another tangent, then. What did you say the volume of the roasting chamber is in your TO roaster KK? And what volumes did the previous (perhaps less successful) iterations have? Anyone else... what roasting chamber volumes do you use and what % of it is filled with green beans? Cheers Stuart.
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stuartgrant	#31 Posted on 09/11/2009 12:17 AM
Newbie Posts: 36 Joined: September 01, 2009	Just another FYI: Been looking at air flow of heat guns. Most are: 250 l/min on low setting (if applicable) - 8.8 cu.ft/min 500 l/min on high setting - 17.7 cu.ft/min I was surprised to discover that the HG we use (Ryobi 2000W LED) can be used on the lower fan speed at up to the 550C setting (ie. 90% of full heat). Might have to try that. Carefully... as Chad pointed out above. I'd love to know how this compares to turbo ovens, but this info isn't easy to find. Does it say on the box anyone? I might email someone at Tiffany! Cheers Stuart.
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Koffee Kosmo	#32 Posted on 09/11/2009 6:47 AM
Administrator Posts: 1620 Joined: December 31, 2008	Quote Another tangent, then. What did you say the volume of the roasting chamber is in your TO roaster KK? I have calculated my current roaster volume with false floor it is * 11 litres Go to this site and find out what is your roasters volume http://www.online...volume.php Quote And what volumes did the previous (perhaps less successful) iterations have? 15 litres in volume at the start of the modifications Don't forget that insulation has been a contributing factor as well as the speed of agitation as noted below Just today I roasted a 900gr batch just as an experiment As I have been testing different power supplies for the new Kit Roaster The original roaster that everyone knows with the window winder motor is not fused and the more amps you give it the faster is spins I used a 12 Volt 5 Amp lap top power supply 70RPM was the agitator speed Single batch 900gr of PNG Kinjibi AA First snaps 10.30 min Rolling FC 12.10 min Second snaps 18 min but slow Building to good SC at 20 min Did it without a hiccup Quote I'd love to know how this compares to turbo ovens, but this info isn't easy to find. Does it say on the box anyone? I might email someone at Tiffany! The Tiffany TO fan is very gentle It is softer than a regular fan forced oven If I was to guess at the RPM of the chaff spinning at the bottom it would be approx 50 rpm so not fast or forceful at all but it is a closed system so the heat penetrates the beans with a little help of pressure Here is a photo of that 900gr batch KK Koffee Kosmo attached the following image: Edited by Koffee Kosmo on 09/11/2009 8:29 PM I home roast and I like it. Designer of the KKTO Roaster Build information https://homeroast...ad_id=1142 https://docs.goog...lide=id.i0 Blog - http://koffeekosm...gspot.com/ Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex, (KKTO) Turbo Oven Home Roaster.
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farmroast	#33 Posted on 09/13/2009 11:01 PM
1/2 Pounder Posts: 295 Joined: December 20, 2006	Agitation is to heat transfer as the grinder is to espresso. Well designed aggressive agitation greatly improves heat transfer. Mechanical agitation is the easiest to keep consistent but the design needs to be complex. Fluid bed are tough to get the bean action just right. Higher bean agitation makes more noise and harder to watch and for off the shelf roasters I think are common complaints and why many are too tame. Hearing first crack tells little to me anyway. Bean temp and roast chamber temp ET will tell you more about how the beans are reacting to the heat being applied. The Loring roaster uses a fixed drum with moving paddles. I went the convection oven top for it's direct heat application. Spread out evenly over a decent sized area. I supplement a lower plate heater to balance the heat application top to bottom. Then added high speed bean bats to get the beans airborne. The heat gun is direct application but the application is small in area. Ed B. DreamRoast 1kg roaster, Levers, Hand Mills http://coffee-roa...gspot.com/


Koffee Kosmo	#34 Posted on 09/14/2009 6:13 PM
Administrator Posts: 1620 Joined: December 31, 2008	Thanks for that input & nice to hear from you again Ed I had a gut feeling that if the agitator speed was increased it was possible to roast a larger batch Just goes to show the tweak-ability of this TO design. It's one of my favourite things about it However apart from the great roast results, another one of my favourite parts is the chaff separation I love to tinker KK I home roast and I like it. Designer of the KKTO Roaster Build information https://homeroast...ad_id=1142 https://docs.goog...lide=id.i0 Blog - http://koffeekosm...gspot.com/ Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex, (KKTO) Turbo Oven Home Roaster.
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