MyRoaster V2 (direct-drum)

Roasters and roasting

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Postby Joris » Sun Feb 01, 2009 8:08 pm

In fact it's quite uneven... Have to change the vanes to achieve better mixing.
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Postby Joris » Thu Feb 12, 2009 8:34 am

OK, I have been practising roasting with my roaster now for a while and found 2 more flaws.

First, the vanes inside the drum, they are straight and don't mix the beans enought. I solved this yesterday by making new vanes which also move the beans from back to front and vice versa in the drum.

The other problem is less easy to solve. I have noticed a defect in all the coffees I roasted, a smokey/ashy taste. I think this has something to do with the smoke trapped in the roasting chamber and drum. I could try to add a extractor fan but since the temperature of the air is quite high i doubt any fan would be able to take that heat without breaking down....

Anyone any thoughts on this one ??
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Postby GreenBean » Thu Feb 12, 2009 9:02 am

Joris wrote:The other problem is less easy to solve. I have noticed a defect in all the coffees I roasted, a smokey/ashy taste. I think this has something to do with the smoke trapped in the roasting chamber and drum. I could try to add a extractor fan but since the temperature of the air is quite high i doubt any fan would be able to take that heat without breaking down....

Anyone any thoughts on this one ??


My initial thoughts:

1. Blow the air in via a (very) small fan and a restriction. You would need to be careful to ensure the cold air enters in a place it can warm up without cooling the beans.

2. Extract the air via a larger fan mixing a small flow from the roaster with a larger flow of cold air to ensure the combined flow through the fan is cool.

3. Experiment with natural convection through a flue with a flap to control the flow of air.

I would try 3 first I would expect that a 25 - 40 mm dia flue approx 300 mm long would provide more than enough flow and you would end up throttling it to reduce the flow.
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Postby Joris » Thu Feb 12, 2009 9:16 am

Thanks mate :)

I think I have to check if the smoke problem exists in the drum (which is perforated but might hold the smoke due to unsufficient airflow), in which case option 1 sounds like the best to implement. Small fan blowing air in metal piping which runs around burner to heat up the air. Now why didn't I think of that myself ?

If the smoke problem exists in the roasting chamber and drum (e.g. smoke does not leave roasting chamber so the drum stays filled up with it as well) then option 3 sounds like a plan (and even easier to implement).

Well, I think I know what I'll be doing this weekend ;)
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Postby GreenBean » Thu Feb 12, 2009 9:35 am

I have just had another look at your roaster design and photos and I am now concerned that I may have made an incorrect assumption about the design.

I was assuming that you have a front cover for the roaster although this is not shown. If I am wrong and you use it as shown in the photos then I wonder if your problem could have other causes. As shown in the photos there would be a very large flow of hot air out of the open front of the machine (and cold air in at the bottom to replace it. This would require a large heat input and large temperature gradient over the roaster. The ashy taste could be simply charing of the beans due to the high heat input.

If you do not use a front cover it may be worth experimenting with a simple loose cover for the front of the machine to dramatically reduce the air flow, heat input and temperature gradient over the roaster.
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Postby bruceb » Thu Feb 12, 2009 10:10 am

Joris, I have a question to the basic design. You are using a catalytic heating element whereas commercial gas-powered roasters usually use open flame heating. Have you noticed that chaff falls onto the catalytic elements and burns up, possibly producing more smoke? Or does the chaff all get carried up and away by the current of hot air?
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
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Postby Joris » Fri Feb 13, 2009 6:54 am

GreenBean wrote:As shown in the photos there would be a very large flow of hot air out of the open front of the machine (and cold air in at the bottom to replace it. This would require a large heat input and large temperature gradient over the roaster. The ashy taste could be simply charing of the beans due to the high heat input.


I hadn't considered that yet. There is quite a difference in the roasting chamber temp (measured underneath and above the drum), which reduces as the temp rises. From halfway through the roast the temp difference is quite small. On the other hand, when I break a couple of roasted beans they are the same color inside and outside, ok maybe the outside is a tiny bit darker but it's not black / charred as far as I can tell.

Another thing, the previous vanes in the drum had a couple of gaps in which beans got stuck (a total of 15 / 20 beans). Those beans were complety charred, might that be a possible cause (e.g it "tainted the entire batch through the smoke released by burning up) ?. Anyway, I'll make a cover for the front and will try to do a roast without it (but with the new vanes where no beans can get stuck and burn up, it also mixes the beans better so should yield a more even result) to set a baseline. Then I'll do a roast with the cover. Then after degassing for a bit taste will tell :)


bruceb wrote:I have a question to the basic design. You are using a catalytic heating element whereas commercial gas-powered roasters usually use open flame heating. Have you noticed that chaff falls onto the catalytic elements and burns up, possibly producing more smoke? Or does the chaff all get carried up and away by the current of hot air?


I use a large burner (cast iron) with open flames, I replaced the one you see in the pictures since it was unable to generate enough heat (roasting times of up to 26 minutes to reach 1th).
There is not that much chaff which gets out the drum, the holes in it are quite small so most chaff stays in the drum. In the drum the chaff does not catch on fire and the little bit which escapes the drum burns up even before landing on the heater. The smoke generated by that little bit of chaff burning up is not enough to taint the batch I think, I could be wrong though.
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Postby bruceb » Fri Feb 13, 2009 9:18 am

Joris wrote:Another thing, the previous vanes in the drum had a couple of gaps in which beans got stuck (a total of 15 / 20 beans). Those beans were complety charred, might that be a possible cause (e.g it "tainted the entire batch through the smoke released by burning up) ?.

That will do it for sure. It only takes a couple of burnt beans to impart a smoky or burnt flavour to a batch. It will be interesting to see whether that was the cause.

I'm glad to hear that you are using a bigger burner. I had some reservations about using that space heater.
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
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Postby Joris » Fri Feb 13, 2009 12:17 pm

The space heater was definitely not the best choice ;)
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Postby espressomattic » Fri Feb 13, 2009 5:30 pm

Just my thoughts mate after speaking to and seeing some old probats down here...

Some of the really old probats have this strange flue system that allows you to 'Profile' the smokey taste. From what I have seen it is a simple flue that traps hot air and smoke. To quote one of the guys here 'Ireally freaked me out so I don't use it'.

Another example would be from a roaster in Auckland. I noticed a really burnt smoky taste and called him up. He had a flue valve and had left it closed inadvertently, thus trapping a load of smoke and tainting mega batches of coffee :( .

I don't know how that will help, but needless to say, nice bit of kit and truly envious ;) Not a feather in sight though Joris!
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Postby bruceb » Fri Feb 13, 2009 7:10 pm

You know, Joris, old Breako may have hit on something worth thinking about, namely putting a chimney on the housing. You will need to put a damper in it so you can control the heat loss, but you may get a better heat distribution and get rid of the smoke as well. I've been studying steam engine boiler design recently (don't ask) and the effect of a flu or chimney on a fired heating chamber of any kind is decisive.
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
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Postby espressomattic » Fri Feb 13, 2009 9:32 pm

bruceb wrote:You know, Joris, old Breako may have hit on something worth thinking about...


Well it was bound to happen at some point ;)
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Postby bruceb » Fri Feb 13, 2009 9:57 pm

espressomattic wrote:
bruceb wrote:You know, Joris, old Breako may have hit on something worth thinking about...


Well it was bound to happen at some point ;)


Of course we don't know for sure yet that it means anything at all... Image
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
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Postby CakeBoy » Sat Feb 14, 2009 12:39 am

espressomattic wrote:
bruceb wrote:You know, Joris, old Breako may have hit on something worth thinking about...


Well it was bound to happen at some point ;)


No, no I won't have that. I often think about flying portafilters actually :P

We finally made it to The Twilight Zone! I seem to have come over all light-headed and unnecessary ..... have to lie down for a bit :shock: :P
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Postby GreenBean » Sat Feb 14, 2009 8:07 am

GreenBean wrote:3. Experiment with natural convection through a flue with a flap to control the flow of air.

I would try 3 first I would expect that a 25 - 40 mm dia flue approx 300 mm long would provide more than enough flow and you would end up throttling it to reduce the flow.

Joris wrote:Thanks mate :)
If the smoke problem exists in the roasting chamber and drum (e.g. smoke does not leave roasting chamber so the drum stays filled up with it as well) then option 3 sounds like a plan (and even easier to implement).

espressomattic wrote:Some of the really old probats have this strange flue system that allows you to 'Profile' the smokey taste. From what I have seen it is a simple flue that traps hot air and smoke. To quote one of the guys here 'Ireally freaked me out so I don't use it'.

bruceb wrote:You know, Joris, old Breako may have hit on something worth thinking about, namely putting a chimney on the housing. You will need to put a damper in it so you can control the heat loss, but you may get a better heat distribution and get rid of the smoke as well. I've been studying steam engine boiler design recently (don't ask) and the effect of a flu or chimney on a fired heating chamber of any kind is decisive.

Etc. Etc. Etc.

Ahemmmm.... Guys. :D :D :D :D :D :D :D :D
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