Hi & welcome to HR endlesscycles

The only one I know of is a commercial roaster
Called the Chinook Air Flow Roaster

http://www.coffee...ourmet.htm



KK

Welcome Marshall! I'm on a very similar quest, only Im content to stop at a 2 pound batch. If you have an entire day and some coffee and snacks, check out:

http://forum.home...ead_id=984

Where I've documented my excursion thus far.

To sum up, I'm very convinced you can loft 5 pounds of beans with a vacuum motor (I use a Kirby). Second, you can get more than enough heat with a propane torch. I know these facts from RoasterRob over in New Zealand who has been the forerunner home-air-roaster. Check out his roasters in this thread:

http://forum.home...#post_6964

Be prepared to be amazed.

Do you have any plans drawn up?

CHAD

Here is how the 500gr / 1.25 pound Sivetz hot air roaster works

May help some people
KK

EC, Check out my lofting spreadsheet in the Downloads section.

Five pounds is trickier, like you say, but not impossible for a DIY. A buddy of mine is roasting commercially on a 20# homebuilt unit. Generally speaking, tou need enough pressure to loft, but not so much volume that you are wasting heat.

A large vacuum motor (Shop Vac) should get you enough pressure and flow when you use its exhaust as a prime mover. Or, a high pressure centrifugal blower running at elevated speeds.

To answer your question, here are some rules of thumb I have discovered or remembered:

Generally, keep your bean depth no more than your roasting chamber diameter. Make the perforated disc about 1/4th the diameter of the roasting chamber. A 30? funnel shaped bottom is good.

Good luck, Dan

Dan, how does your friend heat 20#?

CHAD

He uses electricity. Specifically, an industrial, self-contained heater called a heat tube. The heating elements are housed in a 4" diameter, 24" long (approx.) steel tube. The air from two vacuum motors funnels through it on the way to the roasting chamber. A PID controls the heat.

Thanks, Dan. I just came across this roaster, too. He has a turkey fryer propane burner on the blower inlet. Interesting.

http://coffeewisd.../photo.htm

CHAD

That looks too easy! What sort of fan can actually handle that kind of heat? While a $20 used vacuum motor sounds great, I'd rather spend a little extra to simplify the design.

It just so happens that I have the exact same blower this guy is using in the video. It should be able to tolerate all sorts of heat - the only catch being how much travels along the motor shaft to the bearings. If you rigged a coupler and/or a "heatslinger" (thanks Dan for the lingo), that should be plenty of isolation for the motor, but the guy in the video uses neither.

The reason I did not pursue this arrangement after I bought the blower and motor was that the universal vacuum motor can be easily speed controlled by a timer/triac circuit, pulsing the AC. The AC motor with start/run cap requires a Variable Frequency Drive motor control, which was more than I wanted to invest in the project.

If you're interested in this blower/motor I am willing to sell it. I think this is the blower and motor I have:

http://www.graing...tems/7D747

CHAD

That rocket will fly!

What's that in the middle? Heat source? And, you say "2lb stovetop version", will the stove provide the heat?

Questions, questions, questions.

(Your Kirby will ship on Monday. Sorry for the delay!)

CHAD

I expect the general weight of the beans will keep the unit from blowing off the stove and becoming a hovercraft.

CHAD

Hi Marshall

Probably not much that i can add that you can't read in my posts in other roaster threads.
I would encourage you to have a go at building the asymmetrical roast chamber like mine. Reason being it requires less energy to loft the beans than the cone type. My current RC is 6" dia and roasts 2.3kg (5lbs) comfortably. Not sure how much i have roasted with it but it would be well over a 1000 roasts by now.
The bean to bean contact in the cone type chamber creates more resistance between the moving column of beans and the surrounding beans. The bean column in the asymmetrical RC has shiny stainless steel around it for over half the periphery of the moving column.
JMO but this type of RC is easier to build than the cone type.

my 2c worth.

cheers

Rob vL
NZ

Hi Marshall,
I've said it before and I'll say it again, we should listen to what Rob has to say. He is very methodical. Lofting 5 pounds of beans is dead easy. There are other things to worry about.

Hi Rob, I have an almost finished copy of your 5lb roast chamber sitting in my shop. The basic work only took an hour. As you say, very much easier than a cone bottomed RC. I'm hoping to build a dump door into it like the one you made for a friend. I really need to finish it as I have concluded that there are a few reasons why your design is better than mine. Why are you building a cone roaster?? We could just trade ;)

Hiya Dan, I don't think Wes is using his PID yet to control heat. But I could be wrong, most of the time I don't return his phone calls(bad me). Yes, he is able to loft 20#s with two motors. I use 1 motor that is an upgrade from his and am able to loft over 12#s. I happen to (respectfully)disagree with your statement about bean bed depth related to chamber diameter though. The reason is this: I have only had enough available electrical power in my shop to roast 6 pound charge in my 12 pound roaster. My roast chamber is round with cone and is 11" diameter. The result is that my bean bed depth is pretty shallow. This causes two things to happen. 1- erratic bean spouting(yes, this is related to perf hole size and number. Remember that this was designed as a 12 pound roaster). 2-(Most important) heat transfer sucks. I am wasting a lot of heat/power because of this. Both Wes and I have TC's to measure air temp just before entering the roast chamber and we are both WAY high for the best sort of roast and flavor profile(I shamefully disclose my air temp to be over 750F for a bean finish temp of 444F. The ideal is to not be over 560F air temp). Pay attention to this!! A deeper bean bed like Rob's WILL result in lower roast air temps to get your coffee to FullCity which DOES make for better tasting and slower staling coffee. There is probably a practical limit to the bean bed depth(incidentally, pressurizing the roast chamber has some very real benefits). I use a non-contact IR Thermocouple to read the spouting bean temp and compare it to roast air temp and bean bed temp which gives me an idea of the heat transfer. The closer bean bed and spouting temps are, the better. And the lower the roast air temp for a given ramp the better. The funny thing(easily explainable) on my roaster is that subsequent roasts after roast #1 and #2 require a lower roast air temp to achieve identical roast profile.

Oh yeah, one other thing. Keep your blowers as close to the roast chamber as possible! Wes with his air roaster actually mounted his blowers in another room and piped the air to the heater tubes. This allows the air to be compressed to the point where the pressure finally overcomes the weight/resistance of the beans and results in a big "hop" of the bean bed. Then it collapses until pressure is built up again(Even Sivetz' 1/4 bag air roaster, which the pic in the second post is based on, has bean bed hopping). Wes and I were both pretty perplexed by this as it did not always happen(more on his than mine) but was bean and temp dependent (bean screen size and density). Simply put, the air acts like a spring, coiling and uncoiling. The beans are literally bouncing on a column of air. The resultant bean hopping is kind of cool to watch and I think actually results in a better heat transfer, but it's not really the way we want to do things since I have found it difficult to do it all the time on purpose. Especially keep the volume between your heat source and the entry to the roast chamber to a minimum because hotter air is less dense and is easier to compress(Dan, am I right about that?). Of course, if you are burning propane you don't want the flame too close to your beans either, so you will have to find a happy medium. Rob would know how close you can get.

And as far as the angle of the cone, simply pour a bunch of beans on the table and measure the angle the beans come to rest at in the pile. Make the cone the inverse angle but a bit steeper(or a lot) than this "angle of repose".

Sorry, I very rarely check in here(which is terrible) and have just walked in and brain dumped on you all. Feel free to throw mud and discredit me as you are able. I am just an empirical roaster slowly slogging my way towards automation and good tasting coffee. I never seem to get it all figured out. Right now I'm getting my behind kicked by the densest Panama I've ever seen. I can't seem to keep it from stalling half way through first crack, even at FULL POWER and a very steep ramp of 30F/minute coming into first. EVEN with air temps of 780F!! I've tried longer drying phases etc. This is why I need Rob's roast chamber design with a very deep bean bed and super heat transfer. Oops, I'm getting verbal diarrhea here. Better stop;)

Happy roasting to you all,
Erik

Hey, Rob and Erik! Great to have you poppin back in!

With regard to bean bed hopping, I've found it to snuff the torch out on occasion too.

Is the asmetrycal roast chamber something like this:

CHAD

I've just read everything rob has posted on this site. Wow.
Back to the drawing board.

Hi Erik

Most of what you posted made sense to me. Will reply longer when i have a bit more time.

Hi Chad

Yup thats the one on mine the flat part with the perfs is 'D' shaped and approx 1/5 the diameter wide. The sloped plate is 4/5 of an ellipse. Parts are easy to cut even in stainless using a 1mm cut off disc and a sanding disc to finish the shaping of parts. I was gob smacked how smooth the flow of beans is using this setup.

Hi Marshall

If you want any more details on mine let me know.

cheers

Rob

I wanna be gob smacked.

CHAD

Before you try to patent your roaster, check out
http://www.sivetz...patent.htm

I have no intention of patenting.

I am well aware of of the various Sivetz roasters and the patent relating to them. It was much discussed on A.C earlier this century. Ted Simpson made a 1 lb version of the asymmetrical roaster first with electric heaters then with gas.

Are you sure that is the url you were looking for? That's Sivetz patent regarding freezing coffee.

Rob

Hey Chad,

Yes, that would be the cross-section. The top view could be either circular or rectangular.

Cheers,
Erik

Sivetz' patent ran out long ago. I actually talked my way into his shop past the gate keepers. He wasn't there. A very crotchety and suspicious old man. He should be with guys like me poking around.

By the way, the conical roast chamber is not his idea. That came long before him. His is the asymmetrical design.

Rob, I'm sure that at least some of my post lacked any sense whatsoever. Just help me out and tell me which parts, eh?

Hi Rob,

Thank you for being open with your roaster design. I am concerned that even if my venturi design works flawlessly, the air temperatures may be irregular and difficult to control. Additionally, I am much more interested in roasting 2-5lb batches of the highest quality beans than I am interested in being novel. I understand there are thousands of successful roasts using your design, so I can only assume that it works great. From your images posted on Homeroasters, I have a grasp of the general architecture.

Are there some design details that you are willing to share, such as photos and geometry info (angle, perf diameter and distribution) of the perforated bottom plate of the roast chamber?
Have you found a minimum standoff from the flame that is recommended?

Many thanks,

yup Ted Simpson alt.coffee about 7 years ago. go to google groups alt.coffee and search for gas roaster etc. He tried a venturi setup it didn't work.

Rob

more soon

After building the RC with the dump door i decided not to go there again it worked but was a bit leaky for hot air. Much better to keep it simple. I lift my RC off the roaster and dump the beans, takes 3 seconds. If you want a dump method I would look to do it the way that Wes does with his roaster.



I find the beginning of the roast goes faster on subsequent roasts. I actually cool the roaster between roasts with water. Even so there is still residue heat in the RC so I have the fan up higher and the gas setting lower for the first 3 or so minutes of roasts.



I think with higher pressure there is less bean hopping. Mine tends to do it if I roast the max load (2.3kg) but only in about the last 1 to 2 minutes of the roast. At this point the blowers turned down low so the actual pressure below the perf plate is reasonably low. With 2.2 kg or less I get no bean hopping at all. If the air control was to be via an adjustable valve just below the perf plate the pressure could be high with very little room between the valve and the perf plate for the compression/ decompression effect.



The gap from the top edge of the burner nozzle to the plate below the RC on an earlier roaster is about 11" which makes the total distance from burner to the beans about 13". On later roasters i have increased this by about 6". I would go for at least 15". Flame length is approx 8" at a guestimate. Ted Simpson used a small bowl or similar above the flame as a means of decreasing the direct radiant heat from the flame on the beans at the bottom of the RC.



I really don?t disagree with any of the conclusions you have come to Erik. I have come to much the same also by empirical means.

Rob vL
NZ

I've bee dragging butt on this project. Got sick about three weeks ago and have been very slow to recover.

Sourcing materials has been a chore.
Finding a burner that is in the right heat range is absurdly difficult. The fact that much of the design hangs on having the burner first, trying out options in-situ doesn't seem feasible.

Lesson: tubing over 2" is called pipe. It took me several weeks of internet searching for 6" stainless tubing to figure out it didn't exist, at least by that term. Ridiculous. I found a 24" section of 6" schedule 5 pipe for $140. Rolled and seamed 24guage sheet made to order is a cool $55.

or.....

$1 (one dollar) at the scrap yard: