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allenb
12/04/2022 9:18 AM
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Heat Shield Question
rbisch
Hello, I've been a long time lurker here to build a roaster that will be for my school project. My question is, if I put a heat shield between the burner and the drum will it reduce the effectiveness of the roaster? I saw that most roasters have heat directly hitting the drum. My assumptions are that the beans would cook more evenly if the drum wasn't directly above an open flame. I will be using an 8"x12" drum with some perforations, a propane burner made out of a 1" pipe, and I was planning on using a 9"x13" baking pan as the heat shield. The heat shield would also act as a chaff tray. Cheers
 
Mad Mac
A heat shield keeps the heat inside and around the drum. That's its purpose. The rotating drum evens out the roast.

Heating outside the heat shield is not a good idea because you'll be wasting heat. You can get the inside hot enough but you will use more heat than necessary because the heat shield dissipates heat directly to surrounding air.
 
Koffee Kosmo

Quote

Mad Mac wrote:

A heat shield keeps the heat inside and around the drum. That's its purpose. The rotating drum evens out the roast.

Heating outside the heat shield is not a good idea because you'll be wasting heat. You can get the inside hot enough but you will use more heat than necessary because the heat shield dissipates heat directly to surrounding air.



Good answer and correct MM

For RBisch
Keep us in the loop with build updates and photos
We will make a coffee roaster out of you and your enthusiasm

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.
 
allenb

Quote

rbisch stated: The heat shield would also act as a chaff tray.


If the heat shield is horizontal, has heat from the burner hitting it and has chaff collecting in it then we've got a problem. You'll have the chaff smoldering for a while then will ignite into a nasty chaff fire. As posted above, you'll be better off with a shield if the flame will contact your perforated drum but use an upside down V instead of a pan so chaff and other particles can slide off. Make it a little wider than the pattern of the flame.

Ideally, for solid drum, it's better if the tips of the flame are slightly below the drum surface but I've done quite a bit of roasting with the flame touching the surface of my solid drum and have not had any problems with heat distribution. On the other hand, my burner has a very constant output throughout its length. Flames touching the surface of a perforated drum will roast nicely but will require a totally different approach since this will be direct flame roasting and from all I've read, it is difficult to master.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
rbisch
Thank you so much for the responses! @MadMac the heat shield, drum, and burner will all be enclosed in essentially a box (a didn't make that very clear) so it was more of a question of hitting the perforated drum directly with heat. @allenb your response really helped! Would letting the chaff burning be a serious problem? I roasted in a whirley pop over an open fire and I'm assuming that this burned the chaff as well? If the chaff fire is more of a smokey, smell issue then it won't bother me as the roaster is designed for outdoor use. But if the chaff being burnt will cause an issue in taste is this what you are suggesting (picture)? It seems that the chaff may still smolder on the base metal.
 
rbisch
Sorry, picture was too large and didn't attach. Here it is. http://imgur.com/...
 
Mad Mac
Nothing is stopping you from pursuing your design. Just keep us posted. Build pics will be nice.
 
Koffee Kosmo

Quote

rbisch wrote:

Sorry, picture was too large and didn't attach. Here it is. http://imgur.com/...


With a perforated drum - there is nothing stopping you from placing the heat source at 25 past or 25 to on the clock

I like breaking all the rules ThumbsUp
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.
 
Ringo
I can note exactly remember the story or what company it was taking a bought. They were explaining how there drum roasters work. They had two conventional flame under drum burners and and one with the burner outside the drum. They said different coffees are better in different roasters. I believe the company was Inteligenzia.
All you need in life is ignorance and confidence, and then success is sure. Mark Twain
 
allenb

Quote

rbisch wrote:

Would letting the chaff burning be a serious problem?


Yes it would. Burning (not deep browning) produces a nasty smoke that would alter the coffee's taste. Also, once in flames, your ET would be all over the place and most likely cause barbecued, flame broiled coffee.

As long as you keep the inverted V width not much wider than the flame path and keep the angles steep, then stuff should slide off pretty well. I like KK's idea, to place the burner off to one side (the side the coffee will not be traveling upward on the drum wall). If you do that then I wouldn't bother with a shield at all.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
allenb

Quote

Ringo wrote:

I can note exactly remember the story or what company it was taking a bought. They were explaining how there drum roasters work. They had two conventional flame under drum burners and and one with the burner outside the drum. They said different coffees are better in different roasters. I believe the company was Inteligenzia.


Their Gothot's have the burners discharging into the upper side of the drum enclosure instead of underneath. The "belly dump" machines required this at least with the Gothot versions. For this type of design to function properly, there's a limit on the minimum allowed negative draft into the roaster to ensure the combustion gasses travel an optimum path into the side opening and around to the back side of the drum. Very nice roasters!

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
rbisch
Great thanks for the help and ideas! I will do a little redesigning then. I'm not sure if I am going the inverted v, the offset, or both yet. As far as keeping you gents in the loop should I just keep posting in this thread or start a new one?
 
allenb
I would start a new one to cover the complete build project. Place the new thread under Building a Roaster - Drum Roasters and include in the title your intended batch size in kg. Everyone loves to see new builds here! woohoo

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Erik

Quote

rbisch wrote:

Great thanks for the help and ideas! I will do a little redesigning then. I'm not sure if I am going the inverted v, the offset, or both yet. As far as keeping you gents in the loop should I just keep posting in this thread or start a new one?


I don't know if it is a good idea but my new roaster has a removeable copper sheet wrapped around the perforated drum.
Erik attached the following image:
dsc07051-2.jpg
 
rbisch
Alright, I'll make a new thread once the build starts up! That copper is in interesting idea. Must just be to transfer more heat to the beans? Have you noticed a difference between your copper rapped drum and a normal one?
 
Erik

Quote

rbisch wrote:

Alright, I'll make a new thread once the build starts up! That copper is in interesting idea. Must just be to transfer more heat to the beans? Have you noticed a difference between your copper rapped drum and a normal one?


No. I just got this roaster, my first step up from a whirly pop, yesterday, so I don't have any idea. The instructions show that you can remove the copper if desired (at least I interpret it that way - it is in korean and the picture shows them taking off the copper).

I will say that the roaster seems to heat pretty quick and hold heat very well.
 
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