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Commercial Drum Design
sdcoffeeroaster
I found this on an Aussie coffee site. I think it's Diedrich drum.
sdcoffeeroaster attached the following image:
diedrichDrum[975].jpg

Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
dBndbit
Plenty of stirring vanes, and all of them slanted to move the beans sideways in both directions! Any idea how full the drum is with a maximum batch loaded? Looks like there are slanted vanes to stir beans around the axle. Also it looks like the outer vanes are moving the beans sideways opposite to the "higher" vanes around the axle, so maybe the beans cycle from the front of the roaster to the back? Any idea what the rotating speed is?
Jim
11 years old... forever!
ReeferDoor.com
>home-built roasters and fair trade
 
Dan
Neat picture, and a window into stationary drum roasters.

I would imagine that these drums are filled a little fuller than most if the vanes around the axle (moving the mass to the back of the drum) are going to negate the action of the vanes on the inside of the drum (moving the mass to the front of the drum).

Note how severely angled the drum vanes are, about 45?. Many of the home built drums are not angled. While angled vanes reduce lofting the beans as high in the drum, there is a good reason for these vanes to be angled. They help to empty the drum when the dump valve is opened.
 
sdcoffeeroaster
I knew you guys would find that one interesting like me. My vanes are angled, but more like the Behmor. And with a riveted assy, it tends to flatten sections of the drum if the angle is too severe. But I tested its mixing with red and black colored beans in a load and they were moved all over the drum within about 15-20 rotations.

I can almost picture the beans in the diedrich roaster being pushed to the front, piling up, and then tumbling back to mid drum. I'm just not sure about the middle vanes and would have to see how deep the beans are in the drum or the drum capacity. But diedrich is noted for being able to roast fairly small percentage of the drum capacity with good results. Oh and the Diedrich is noted for higher than normal air flow I think. Maybe it help direct that flow into the bean mass...just guessing here.

Here's another larger one...and different. I think it's US Roasters
sdcoffeeroaster attached the following image:
USRoastersDrum[977].jpg

Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
Spresso_Bean
I have never seen pictures of how the drum fits against the front plate (where the trier and hoppers usually are) - is there some sort of groove or lip that the drum rides against? I can't imagine there's a groove because that might affect the beans going down the drop chute, but I could be wrong. I am looking to try and build a small version of something like this, but I'm still not sure how to design the interior which isn't very common to see in pictures. I like the pictures up above of the commercial drums, though.
 
sdcoffeeroaster
You probably noticed how thick the first drum looked for its size. And how perfectly round the drum is. My guess is that they run the drum right up to within 0.05" of the front plate which is very flat and held relatively perpendicular or normal to the shaft. Everything looks very rigid and so there's not much flexing.

I know some have stationary drums and just the vanes turn too. Figure you have to keep the gaps less than 0.100" or so to avoid trapping beans, especially peaberries. And of course the design has to allow for the usual machining and sheet metal tolerances depending on the parts. But I'm just speculating to be honest and I too would love to see more of the inside of a commercial roaster. I might have to buy one someday to do that and will probably end up doing just that anyway at the rate I'm going, lol...might be cheaper for me too.
Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
Spresso_Bean
Haha, yeah I was thinking the same about buying one but I don't roast enough to make that worth the cost - it would still be fun to have, though. Thanks for the info, and I figured that it could just be so precise that there isn't much of a gap at all. I just haven't found much information about the internal workings of the big roasters yet.
 
Dan
From what I've heard and seen, the drum butts up to the front plate and is adjusted until it almost touches (when heated). If so, this means that those welded drum assemblies pictured above have to be mounted on a lathe for truing then ends.
 
sdcoffeeroaster
Yes Dan and given the price of the roasters, that would not be that out of the ordinary. And it's easy to fixture given its shape and the bearings. And since the inside of the roaster grows some too when it gets hot, I bet they know just how to shim the drum and how much clearance to allow for expansion differences and tolerances. It's probably not all that much.
Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
Dan
Fred, Yeh, par for the course, and its not a big deal if you have the right sized lathe and a small hoist, and like you say, it is easily fixed between centers. Heck, I could do it!

However, the heat expansion for the entire drum is substantial, about 0.090 (3/32") for a 36" long drum. But, if the drum was constrained by the front bearing, then the expansion between it and the front of the drum is much less, probably only 2-3 thousandths, and could be ignored like you say. Personally, I'd put in shim washers between the drum and bearing and be done with it.
 
seedlings
A local coffee shop uses a small Diedrich drum roaster. Their coffee tastes horrid. Ownership has changed, staff has changed, but the coffee is still very bad. My roasting buddy has asked them before to sell some of their green coffee so we can see if it's the coffee or the roasting, and the previous owner wouldn't sell, but now they'll reluctantly sell the greens for the same price as the roasted per pound, $11.50-$12.50. I figure it's not worth my time and money. They now only have 4 origin coffees, a couple of blends, and about 15 flavored coffee beans for sale.

So, all that said to ask a question about these commercial drum roasters... are they equipped with preset ramps where anyone with opposable thumbs could roast decent coffee, or is there technique required at all levels?

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
Dan
I suppose you could get a number of controller options on those units. The one time I watched someone roast in a store was a half-bag in a drum. He got the thing up to temperature, dumped the beans. Their thermal mass brought the temps way down and then began creeping up, creating their own curve. I didn't see him adjust the temperature once. He did turn on the exhaust fan part way through. I didn't see the PID change its setpoint, so it looked fixed, to me. Near the end he checked the roast constantly with the trier. Not much help, I know, but it does indicated that some roasters don't use a lot of finese in their craft.

 
sdcoffeeroaster

Quote

seedlings wrote:
A local coffee shop uses a small Diedrich drum roaster. Their coffee tastes horrid. Ownership has changed, staff has changed, but the coffee is still very bad. CHAD


Is the just the brewed coffee they serve bad or are the roasted beans the issue? A local roaster I know has this tendency to roast too dark for my taste but sometimes stops short of a fiery 2nd crack. They had this Peru I loved and when I went in last it tasted just like something from Starbucks but fresher.

Yes now that I've been dumping my beans into a hot drum I see that turn temperature that Dan is talking about for commercial roasters. If the drum is too hot that temperature is too high and beans can get scorched or too hot instantly. A nice turn temp is around 200 or so but I've hit 230 or 240 a time or two while trying to get used to this technique. I need to be more repeatible with initial temps and opening the BBQ doesn't help. And I don't pour on the heat even at that point but ramp it up gradually watching the bean probe all the time.

How dark do they roast? I wonder how much time they take between 1st crack and when they stop the roast? So many things to pay attention to including brew temperature it's almost like golf!
Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
seedlings
The beans taste bad when I or my friend brew them as well as how they're served in the shop. Since I'm not very interested in their roasting, I don't really know their methods, but the beans are always shining with oil Like you, this is darker than I prefer but there must be bigger problems because a proper dark roast is good none the less. Maybe I'll stop in today and ask them. I'll probably walk in with my travel mug, full of my Huehue, and sip it as I talk to them :@. Tact? What's tact?

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
MarkBart
That's not tact, That's the perfumed hankie over the nose to ward off the smell of the unwashed masses. (Think of Harvey Korman and Mel Brooks as Count DeMonet and the The King in History of the World Part 1) (It's GOOD to be the King!) hehehehehehehehehehehe
I'm so Bad, I'm Good! www.homeroasters.org/php/images/smiley/cool.gif
I'm putting the small back into Small Business!
 
sdcoffeeroaster
So I was looking at the first smaller drum made by Diedrich. Did anyone notice the impeller or screw like features in the center? Looks like the outer vanes drive the coffee into the face plate and then the center ones pull it to the back to create a sort of tumbling effect. You can even see some similar features in the larger drum but it's pretty obvious in the smaller one. This isn't something I ever knew about commercial drums, until now. Interesting design and I can now see why it's so easy to empty it by opening the front hinged door.
Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
seedlings
I find it amazing that the drum must be half full of greens! That is just a huge bed of beans! I'd love to see one in operation with a clear shell, not a computer simulation.

Have you figured out how the Diedrich drums successfully roast a smaller load? Seems like there would be a stuck pile of beans at the door, only tumbling part way back to the middle of the drum.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
sdcoffeeroaster
Yes good point. I'm not sure about the capacity of the smaller drum or even how low you can run it. But I have heard that a lot smaller than max loads can be a problem to roast evenly in some commercial roasters. Maybe this is why. If you visualized it turned on end, the bean motion is sort of like an air roaster, something we don't do in a normal bbq roaster...yet that is.

Wish I could quit experimenting but I'm compelled to at least try? I just finished a DC 24 volt big big gear motor with PWM motor speed control only to find out that faster is better. It was limited to 60 rpm and 45-48 just slowed the roast down too much. Might be a good way to control a "too fast" roast though.

Now I'm trying 80 rpm in my 9" drum and finding it is slightly better and faster. I think that's getting a bit close to the max for this size drum though and the beans, in theory, should begin sticking rather than tumble, at around 88+ rpm.

So far I've found lots of things that slow down the roast and few that will speed it up without scorching the beans.
Fred
Fresh Roast+, I-roast, and 2 BBQ roasters, one with IR back burner (Blue Ember grill from Fiesta)
Espobar Brewtus II
 
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