CoffeeAir - 1kg Indoor Electric Roaster Trial

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

By "waste heat up the vent" I mean the heat that goes out the top of the roasting chamber, and into the sky or a vent hood. Im trying to recirculate the heat, therefore requiring less energy.

Gday Chad,

I guess my concern with recirculating the Hot Air (and Evaporated Volatiles of the beans), purely from a roast quality perspective, is that you are effectively moving away from the principles that sets Fluidised Bed Roasting aside from the more conventional Drum Roasters...

That is, because you are effectively recirculating volatiles from the beans as well, these will inevitably get burnt and further transformed (carbonised & worse)) and more than likely adhere to the beans while theyre roasting.... Not too dissimilar with what happens in a conventional drum roaster actually. What I see as the great advantage of Air Roasting (Fluid Bed) is that any evaporated volatiles are carried away from the beans and will therefore play no further part in the roasting process and results in much "cleaner" roasts that seem to delineate the flavour spectrum more noticably. Most likely because the carbonised volatiles are going up the chimney rather than coating the beans and masking their intrinsic potential.

I played around with vacuum cleaner motors, blowers and gas fired heating methods for a bit when I was popper roasting, in an effort to come up with a practical design for a 1-2Kg home-roaster. While doing this I rigged up a splitter arrangement to recirculate a portion of the "used" heated air to see if this could be utilised to improve efficiencies. Well, it did but at the cost of losing some of the intrinsic flavours from the profile, which definitely seemed subdued compared to when the system was running as a total loss roaster. At around this time though, Belinda came up with the concept of the Corretto and after determining its operating constraints and the ability to produce very acceptable 1.0Kg roasts, my gas fired, fluid bed roaster was put very much on the, errr... back burner. :

Might have a go at resurrecting it one day but at this stage I dont have a workshop and probably wont until next year some time but will also be dependent on how my health holds up too as it isnt too flash lately. Anyway mate, thought I would just throw this into the mix for your consideration. All the best Chad,

Mal.

[Bill]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Im not sure Rob in New Zealand uses a cone, does he?  I was under the impression he uses a flat perforated plate because he likes the asymetrical flow rather than the "pretty" flow.  Rob said it seems more effecient to him.

Well he has used cone types, like this one of his: http://coffeesnobs.com.au/YaBB.pl?action=download;file=10inrc.jpg

But his other designs are like this other one of his: http://coffeesnobs.com.au/YaBB.pl?action=download;file=rc6in1_9kg.jpg

In both designs the perforations dont cover the whole area of the roasting chamber.

My roasters use only 25% or less of the roaster diameter perforated.

(Which he states further down the same page that your quote came from. Actually a photo of his cone type type design is also shown on that same page.)

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Mal, youve been a big help to me before and I do weigh your wisdom carefully!  What youre saying about the volatiles has been brought to my attention before I started the project.  One thing about this roaster is that ALL the air will be recirculated - a closed system.  All the volatiles will pass across the 2000F (1100C) coils over and over, and without added oxygen, hopefully will be burned away.

Actually, now that you mention the drum VS. air roast flavor... a big chunck of the roasting world might actually prefer the drum-styled profile over the fluid bed air.  Not me, though, as my coffee tastes originated with air roasted.  I tried the drum for a while, but dont prefer it.

My goals are:
1) All-in-one roaster/cooler/de-chaffer that will run off a normal 20amp 120VAC electric circuit.
2) Variable load size from 0.5 pound to 2 pounds and everywhere in between.
3) Able to reach first crack in 10 minutes at full load, 15 min to second crack.
4) Smokeless for indoor use.
5) Uncomplicated to load and unload into bags or jars.
6) Built-in chaff collection.
7) Less than $100 in new and used parts.

If it tastes more like a drum roast, thats OK by me if it does all these things well!  My primary goal all along is #4.

------

Bill, it looks like Rob uses a couple of different methods, then.  Id still love to see one of his beauties in person!  Thanks for your suggestions.

------

UPDATE: Im having trouble with the heat coils. Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked. In test runs there just wasnt enough heat as it is now.

CHAD

[JavaB]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Chad,

Whilst the concept of...

4) Smokeless for indoor use.

would indeed be great..... Im very much in Mals camp..... you will have lots of volatiles and/or smoke passing through the beans over and over again! These will taint the flavour of the beans I have no doubt.

In a true fluid bed roaster the smoke and volatiles are immediately exhausted and dont have a chance to affect the bean flavour.... in a drum roaster a significant portion is exhausted (under the control of the operator)...... and the flavour of the beans can be altered by the quantity of the airflow....

However in your design 100% of the smoke/volatiles will be passed through the beans - over and over again..... and this will certainly have an impact.

If you like the taste of fluid bed - Im sure you wont get it (or even close to it)- my guess is that they will taste like an extreme drum roast..... one with no airflow through the beans at all.

The resulting roast could be very nice (depending on your taste preference)..... but Im certain will be nothing like from an air bed roaster..... and will be even more "drum roasted" than you would get from a drum roaster.... if you get what I mean.

Good luck.... I will be interesting to hear the results.

[Koffee_Kosmo]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

UPDATE:  Im having trouble with the heat coils.  Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked.  In test runs there just wasnt enough heat as it is now.

CHAD

Chad
Have you considered an oven coil heat element that is used as an extra heat source for the fan forced oven?
It is small, compact, and I am sure bendable.
It also has the advantage of if it blows it is easily replaceable
KK

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

The resulting roast could be very nice (depending on your taste preference)..... but Im certain will be nothing like from an air bed roaster..... and will be even more "drum roasted" than you would get from a drum roaster.... if you get what I mean.

Yep, this is what I discovered with only a partial recirculation of the gasses/hot air... It has to be said though, I love a good roast, what ever method is employed but I do prefer the cleaner and clearer flavour spectrum of an air roast system....

Also, I shied away from using an electric element with this sort of setup as using a simple gas torch with various types of burners and gas flow, I was able to achieve a very useful arrangement, very easily. Chad has hit on the problems you experience with heating elements and air flow, very difficult to arrive at a satisfactory equilibrium that marries heat transfer/transport, an ideal fluid bed action and robustness of the element. The use of LPG gas heating simplifies the establishment of an empirical design in my opinion.

Mal.

[JavaB]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Also, I shied away from using an electric element with this sort of setup as using a simple gas torch with various types of burners and gas flow, I was able to achieve a very useful arrangement, very easily. Chad has hit on the problems you experience with heating elements and air flow, very difficult to arrive at a satisfactory equilibrium that marries heat transfer/transport, an ideal fluid bed action and robustness of the element. The use of LPG gas heating simplifies the establishment of an empirical design in my opinion.

Mal.

Agreed Mal, the amount of heat you can get from electric elements is very limited..... thats why you wont see many electrically heated roasters above about 300gms...... recirculating the air would, in theory at least, provide greater efficiency (just as long as the heat input was greater than the loss of heat from the roaster)..... Gas I would regard as the ideal heat source..... but wont work in a closed system.

The other problem would be controlling the heat. As the heaters have low thermal mass..... and ON/OFF type arrangement wont work very well (As I proved when I tried to PID a corretto). Analogue control would be the go - either a variac, a powerful triac "light dimmer" (for manual control) or ideally a PID with an analogue output (if an automated profile is desired).

Also the HT produces very little smoke (thanks to its rear filter)...... but the moment the beans are dumped for cooling - huge clouds of smoke from the beans once they exit the drum! So that will also be an issue for indoor roasting..... the inbuilt fan could be used (without the heater on)...... but that would take way too long to cool the beans.....

And once you open the chamber - smoke city

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Mal, Java, your points quite valid, and I cant argue any of them. If this wont work out the way Id like, the backup plan is a standard air roaster vented to the outdoors. That method is much easier, just too cliche`.

Why do something the easy way when, after significantly more time, work, and money, I could fail doing it the hard way? My wife REALLY wants to start working on framing the basement....

If this project ever progresses past where I am now, Ill be sure to post the results!

Thanks again all,
CHAD

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Why do something the easy way when, after significantly more time, work, and money, I could fail doing it the hard way? My wife REALLY wants to start working on framing the basement....

Fair enough mate... ;D

Nothing like trying stuff out for yourself, Im the same :. Its all well and good that someone else has tried a design that produced results that they werent particularly happy with, doesnt mean that YOUR design wont perform admirably. Go for it Chad and well look forward to reading about your results.... [smiley=thumbsup.gif]

Cheers mate,
Mal.

[mobbarley]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

UPDATE: Im having trouble with the heat coils. Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked. In test runs there just wasnt enough heat as it is now.

It will probably be hard to heat such a volume of air... you would probably need a very long thin coil or possibly some kind of metal heat-exchanging core which you can heat with the coil :-?

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

UPDATE: Im having trouble with the heat coils. Ive ordered some lighter (24 gauge) nichrome that will get hotter with less current, so once that is in, the heat element will be reworked. In test runs there just wasnt enough heat as it is now.

Have you given any consideration to making an element fashioned into a spiral, supported on a simple framework made from"Micaboard" (a high temperature insulation panel usually used in industrial heating applications - link here). If you can locate a manufacturer near where you live, it is quite inexpensive and would be relatively simple to knock-up a frame that would support the element and allow you to mount it across the direction of air-flow to maximise the transfer of heat within a pipe like structure.

Might give you some ideas mate,

All the best,
Mal.

[beanflying]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Also for heating elements look up Kanthal as an alternate. As it gets hotter the resistance actully decreases slightly (less voltage drop) so the element get hotter when in use rather than cooling slightly like nichrome does.

http://www.kanthal.com/

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Yep,

Kanthal is good.... I think the main problem though is more related to overall thermodynamics of the application itself. Probably need to establish the air flow required for creating the optimum "fluid bed" and once that info is on board, it should be possible to do the sums for heat transfer and transport through to the fluid bed. Location of the "element" will be critical, will need to be quite close to the bottom of the fluid bed and interlocked with air flow so as to avoid over-heating in the event that air flow is reduced excessively or stopped altogether.

A very interesting project indeed...

Mal.

[seedlings]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

I sure wish I could accurately calculate airflow.  All I know is Im using 1/3 of the 6 amps this vacuum motors rating.  I dont know if thats a linear relationship, though... I searched for modern vacuum motors and 120 cubic feet per minute is pretty normal.  So, maybe Im only using half of that?  Hard to say for sure.

Mal, Ive been looking for mica board, but its quite hard to find.  On-line manufacturers want you to order 1000 widgets worth of the stuff.  Im tempted to go to the thrift store and pick up a couple of used toasters and salvage the mica boards from them.

But, Im trying a solution with an item on hand... cement board.  I fashioned a frame from the cement board and wound the new 24ga nichrome around that.  I think Im trying to run the nichrome too hot (12 amps!), though as the first 2 attemts burnt up after about a minute.  Air was HOT though, which is promising.  Im about to start on another element with two 6-amp nichrome wires in parallel.  Im gaining some confidence, though!

CHAD

**edit: Heres the next attempt. 2 coils in parallel for 11.2 ohms. Each coil should see about 5 amps which corresponds to 1300F, well below the max operating temp of 1600F.

[Dimal]

Re: CoffeeAir - 1kg Indoor Electric Roaster Trial

Mal, Ive been looking for mica board, but its quite hard to find. On-line manufacturers want you to order 1000 widgets worth of the stuff. Im tempted to go to the thrift store and pick up a couple of used toasters and salvage the mica boards from them.

Hi again mate,

Do you have any motor rewind shops, industrial heater manufacturers or air-conditioning manufacturers within driving distance of you? Most of these types of businesses will use Micaboard of one form or another and may be quite happy to sell or even give you some off-cuts from the manufacturing/repair process. Might be worth a look.

Sounds like youre making good progress though Chad, using the cement board. I spose the only thing you need to be careful of when using this sort of design is that all of the element coils are in the air-stream; mainly to ensure efficient heat transfer and the avoidance of hot-spots on the elements. Anyway, it seems like its all starting to work out 8-)... Cant wait to see the finished result. All the best mate,

Mal.