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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Building a Coffee Roaster

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Drum Questions
pollywog	#1 Posted on 03/14/2006 11:57 AM
Newbie Posts: 28 Joined: February 18, 2006	I am building a drum roaster, and I've got a couple of questions. Perforated or solid and why? If you prefer perforated drums what is the recommended hole size?


ginny	#2 Posted on 03/14/2006 12:19 PM
Founder Posts: 3476 Joined: October 24, 2005	I would suggest perforated given the fact that you want the air flow and even heat throughtout you roast. Most of the drums I have seen, using BBQ for heat are perforated. There are more experienced drum maker who I am sure will give you great ideas. ginnyB)B)


metal	#3 Posted on 03/14/2006 1:53 PM
1/4 Pounder Posts: 81 Joined: February 05, 2006	pollywog, I have a few schools of thought here. If you have a closed system i.e.. open end drum is close tolerance within 5/32" to a solid fixed head plate (front of the roaster). I could suggest both for many reasons but will make this as simple as possible. If you choose a solid drum in an enclosed or semi enclosed atmosphere make the back of the drum perforated 3/16" hole size works well (you can roast peaberry and still lose chaff). In this case allow for some sort of air control through the front of the drum (on a 5 lb roaster or less have a high temp 60 cfm control fan with no larger a line than 2 inch round will give the velocity at this cfm that you will need. If you do this you will have awesome control over roast profile. If you build this system with control of the air through the drum you will be able to stall the roast at will, or pull heat chamber convection air into the drum when you want it. You will have control over pulling chaff out of the drum at will or letting beans baste in their own chaff broth. in this same air control system it is nice to have control of removing heat from the heat containment chamber quickly also. with these items you can push the chemistry of the bean beyond imagination. If you can't build the above system and are after the bbq type roaster I suggest as Ginny does to have the body of the roast barrel perforated 3/16" holes. No more than 40% open area made of high carbon steel will allow for toughness with little deflection from heat effect (stay the hell away from stainless steel, how people have fallen into this idea that stainless steel is the ticket is beyond me. Just plain bull and I promise to write an article on just this alone) @ 30 to 50 rpm with drum diameter under 10 inches at this speed (over 10 inches is a little different math on rpm). Having perf in this situation will give at least some convection and remove most chaff with the roast chamber being more responsive to the heat containment available. If you like the Smokey coffee vs. clean aspects forget the perf and baste the beans in their own smoke and chaff with a solid drum. Or you may want a drum made of both? ---hope this gives food for thought-- Good fortune to you and happy roasting... oh, my reason for perforated 3/16" hole size is you can roast peaberry screen #14 and still lose chaff without bean loss.


ginny	#4 Posted on 03/14/2006 1:57 PM
Founder Posts: 3476 Joined: October 24, 2005	Bart: Thanks so much for your post; I knew there were wiser folks around to discuss drums. Thanks again, ginnyB)B)


metal	#5 Posted on 03/14/2006 4:54 PM
1/4 Pounder Posts: 81 Joined: February 05, 2006	ginny not wiser s:3 just adding a little to your input. I think I have built all the roasters that won't work so it would be nice to save some the trouble s:8


pollywog	#6 Posted on 03/15/2006 2:07 AM
Newbie Posts: 28 Joined: February 18, 2006	Thanks for the info deleted s:1 You are the only builder that I've read that doesn't recommend stainless. I would like to read more of your thoughts on that when you get around to posting them. I think that probably where most of the hobbyist/builders (at least myself) are coming from is that we are adapters. By this I mean we don't have the tooling (means?) to do a total fabrication so we adapt what we can find which is mostly cookware. Realistically that's gonna be stainless or aluminum. If you've gotta choose between those two stainless is the obvious choice. Metallurgically I'm sure you're right (I'm really new to this but I bet this is an area of much debate), but at this stage of my development as a roaster (22 roasts so far) I'm simply not good enough to spend too much building this roaster. Is there some place where one can obtain a reasonably priced small high carbon steel drum? I'm really ignorant here.:) P.S. One of the reasons that I asked about perfed or not is this page http://www.sweetm...e_pro.html which says this"These are the sample roasters I purchased while traveling in Brazil last year. They are basically a Jabez Burns design, very straightforward. The improvement over a Burns is they have solid drums, not rolled perforated metal." Edited by pollywog on 03/15/2006 2:26 AM


metal	#7 Posted on 03/15/2006 11:28 AM
1/4 Pounder Posts: 81 Joined: February 05, 2006	pollywog, Thanks for the link. Did you notice the drum has holes in the back for air control (not enough holes in my opinion)? Also I see this is a gas unit (cool) that may have direct flame contact with the roast drum. This brings up an interesting point. In my testing and repair of gas units of many types, I find some trouble with perf and direct flame contact if the rpm is to slow (especially if the design is such that the beans are pushed by vane design to one end). What tends to happen if the unit has less than full load is the flame rises into the bean flow where mass is lower and can cause anywhere from "tipping" to a random mix of burnt beans. If I was asked to improve the design you see in the link I would change a couple things. More air control including full perf on the back of the drum. I would improve on burner design (a pipe with many holes drilled in it is poor at best). Chaff will fall from the holes in the back and do two things. 1 plug the burner since this has no flame spreader or protection from the chaff plugging the burner. 2 as the chaff falls out the back and burns on the flame you may have trouble with combustion air loss as the chaff burns up. Since impinged jet is more expensive and not a recommended application on such a small roaster. You need to allow for more, or possibly even forced combustion air in this atmospheric burner situation and this unit seems or looks pretty closed to me. When the combustion area is in situation thats has moisture from the beans flooding the fireplace so to speak it will certainly effect the flame. First the flame will be blue, then as moisture builds the flame becomes inefficent, yellow..For a commercial unit, this one looks like a third grader put it together. Welds are awful and the bearing design is welded into place so as to make it impossible for the average person to replace. I can see why the people a SM decided to not warrant this unit for future repairs. It is a little scary! I think they could take a lesson from "Homeroaster" his is a better design and aplication. I like yer roaster dude, and forget making changes if it's working. One of the problems I have is never giving up the tweeking when it works s:8 Edited by metal on 03/16/2006 7:43 AM

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