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Greetings from Jerusalem plus queries
Argaman
Hi all!!

After a couple of years of roasting in a pot on the stove-top -- pleasant but not so predictable -- I've taken the plunge of getting one of those "rotisserie toaster ovens" as a base from which to build and learn.

Review of the various forum discussions has generated a to-do list that will keep me busy for a long time yet. While I could use some advice about each of them -- noted below -- I have a basic problem in understanding what's going on with my new rig (not a known model).

Basically, everything is clearly moving too slowly. This oven claims to generate 1500 watts, but it takes fully 30 minutes -- in a preheated oven -- to turn 200 g of beans into a real dark roast (my parent's preference, though not mine). 25 minutes generates something more like what I used to make on the stove-top -- just the beginning of the second crack. (I'll try to add a photo of the results)

But here's the confusing part. There seems to be hardly any cracking going on at all! I think that by now I know what to listen for, smell, etc. but almost none of this seems to be happening -- maybe a stray two or three beans first-cracking after 20 minutes or so. How can the beans go from green to almost black and oily without popping? Clearly they do, so I must be missing something... :-(

Any thoughts??


My current to-do list of planned improvements:

1. Insulate the front (glass) door. I've read about covering this with foil for reflection, etc, but since I have no cracks to hear just now, I have to track the beans visually. I keep a disposable aluminum pan on hand to cover the door, so I can easily remove and replace it when I want to look at how the beans are progressing. Maybe I'll rig this up in a more stable way.

2. Add vanes. My drum is 18 cm X 14 cm, but has only one little vane that's some 13 mm high. I'm planning to add two more, taller ones to help mix things more evenly.

3. Motor speed. This creature only produces about 2 rpm, which review of the forums leads me to think is way too slow. I want to open up the oven's electrical insides to see if there's any straightforward way to boost this, or whether I should plan on replacing the motor at some point soon.

4. Fan. The creature came with a fan inside for spreading the hot air; I'm wondering whether its "throughput" can (and should) be boosted.

5. Thermostat. I haven't really had a chance or the need to evaluate the built-in temperature control -- which I presume is not very good. For now, I just put things on maximum (250 C, upper and lower heating elements), since even that seems to be insufficient.

6. Heating elements. I really don't want to start adding or boosting, but if that's what's needed, so be it.

7. Controls. Sky's the limit. If this creature starts to function more or less in a useful zone, I'm prepared to do all the mods needed to get temperature, ROR and so forth under computer control. But that's way over the horizon just now.


A comment on green beans in the Holy Land.
The overall coffee culture here is excellent. After all, we have a great variety of immigrant communities, so that there are continental style "pour-over" fans, lots of Italian style espresso, plus the whole Arab-Turkish Middle Eastern tradition going on at once. That said, home-roasting is very under-developed here, and getting beans can be rather hit-and-miss, and/or expensive. I've never made it to the Druze outlet up north which is supposed to be *the* place (about a three hour drive). But, the bright spot is that we have a substantial community from Ethiopia, and the open-air market in Jerusalem has no fewer than three Ethiopian spice shops, where you can always find decently priced Djimma, Sidamo and even Yirgacheffe beans. I once took home a very inexpensive bag of Wallega beans (having no idea what they were) just on the say-so of the proprietor -- no regrets. Moreover, I suspect that if I scoped the Arab market more thoroughly, I'd find some gems there too. Plus, there are two or three pretty new specialty shops, including one run by a pair of brothers who recently came back from a few years roasting in NYC. Just got some Panama and Kallosi from them...


In the mornings I usually make slightly milked espresso (Rancilio Rocky and Gaggia Classic), and in the afternoons I usually do the IDF/Arabic standard of so-called "black" coffee (which is still called that even if you add milk) -- grinding very fine and then pouring in boiling water.

Many thanks to all in advance. Frankly, I probably wouldn't have gotten the oomph to try this if supportive online forums like this didn't exist!
 
renatoa
Welcome ! BBQ grill

From all the above the best improvement can be due to increasing of the drum speed.
The best way to transfer heat is convection, and for this to happen efficiently there is the first (and only Grin) Sivetz rule: "keep beans moving"... with the later addition, that was probably lost in historian writings... "fast moving" !
Either make air moving faster, as in hotgun or turbo oven setups, either move beans faster in still or slow moving hot air.
In one of my earlier setups, similar to yours, I remember FC time drop from 10 to 8 minutes, or quantity increased from 250 to 330g by increasing drum speed from 10 to 30 rpm.
2 rpm sounds like slow a rolling cage for tortues, if such thing exists Grin I am not surprised about the results.
 
JitterzZ
Argaman
But here's the confusing part. There seems to be hardly any cracking going on at all!

I had some old beans that would hardly crack. I think it might be due to a lack of moisture in the beans.
I would research Behmor for improvements to your roaster. Good luck.
Edited by JitterzZ on 02/24/2019 8:04 AM
 
renatoa
Is also due to the long time of ... baking, this wasn't a roast actually.
Crack is a sudden vapor release from the cellular matrix of bean. When the thermal treatment last too long the water evaporates without a steam accumulating.
 
Argaman
Thanks, renatoa. Your suggestion does seem to explain what's happening. After all, these are the same beans that would crack on the stovetop a few weeks ago.
If this is right, though, does this mean that the system simply isn't getting hot enough to roast? Too much heat leakage and/or not enough heat source?
 
a1970gto
Have you measured the coil? Is it actually 1500 watts? What kind of heating elements are they? Coil, IR, etc? 1500 that should be plenty for 200g. I think what Renatoa is saying that it seems like the heat isn’t transferring, so getting the rpm faster should help the heat get into the beans more efficiently.
 
renatoa
Exactly, for example in an oven with a lot of airflow, so doing convection right, we are using 1300W to bring 600-700 of greens at FC in 10-12 minutes.

The heaters should be hot enough, probably more than 7-800C if halogen/quartz, or more than 500 C if ceramic.
But this heat to be absorbed, you need the best possible circulation of the transfer fluid, i.e. the hot air.
Because inside your oven there is not recirculation fan (I guess), as in a convection oven, then all we can do is to move beans faster.
Is what you did in the stovetop and it worked.
The faster you move them, the more heat will absorb.

How fast is too fast ? when beans remains stuck on the drum due to centrifugal forces you know the drum rotates too fast. The best would be to be carried by the vanes up to 10-11 hours on the drum circumference, and drop from there.

Before hacking the motor/gears, you can try to build a single massive paddle style vane, as is in the Gene roaster, seems the best way to move at once many beans at this low speed.
 
Argaman
Update --

I added into the drum a couple of biggish vanes, which are clearly moving the beans around a lot more (photo). Probably the best I can do with this drum. This increased agitation, unfortunately, seems to have had no effect on the overall "roast" -- probably actually baking -- speed, which is still completely inadequate. thumbdown

I have not measured the IR components, but see no reason (yet) to think they are not as advertised. The circulation fan "works," but may not be providing anywhere near enough airflow.

I still have insulation tweaks to work on around the glass door, but I fear they're likely to be inconsequential.

Here's something (small) that I wonder about. I'm keeping one of the oven racks at the bottom to collect chaff so that it doesn't burn on the lower elements. I figured that preheating things would eliminate whatever impact this has on heat distribution, but maybe that's naive.

So I'm thinking it's time to open things up and see what's easier to boost, the motor or the fan...
Argaman attached the following image:
new_vanes_in_drum.jpg
 
renatoa
Any chance to measure air temperature after some... 5 minutes ?
 
Argaman
Looks like the insulation tweaks were far from inconsequential.

I not only covered the glass door with aluminum foil, but folded the foil so as to seal off the crack between the door and the oven and now, well, what a difference.

I heard isolated cracks (FC) around 13 min, followed by wholesale cracking (SC as it turned out) around 17 min. When the cracking stopped and the smoke started pouring out, I quickly shut things down and found a very deep -- black, shiny -- roast after 18 min. While it's not my favorite cup of coffee, on the fundamental level *that's* more like it.

(I told my Dad that I doubted if it was drinkable, to which he replied "Don't under-estimate me." To each his own...)

Now the "trial and error" phase begins for figuring out how long the kind of roast I like really *does* take in this configuration.

Obviously tweaking the motor and fan will be next on the agenda.
 
Argaman
renatoa, can you tell me more about measuring air temperatures?

I have no idea if the oven's installed thermostat has any accuracy, but that doesn't seem to be what you mean...
 
renatoa
I mean get some oven thermometer like this:

https://www.ikea..../20103016/

... place the probe inside the drum, with no beans, and see how high is temperature reach after some 5-10 minutes of full power operating.

If the thermostat features any temperature marks, what is maximum ?
without at least 230 C degrees real air temperature inside the drum, I don't see chances to improve something, even rotating faster. 250 C would be even better.
 
Argaman
Thanks, renatoa. I'll look into getting an appropriate thermometer.
The "official" maximum temperature printed on the controls is indeed 250 but who knows what it really does.
 
renatoa
When reaching the max, how fast is the cycle between on-off states?
 
Argaman
hey renatoa--

If I'm interpreting the clicks properly, at steady max the heaters are cycling on/off in 25 second cycles. Approaching that, it has asymmetric periods -- 28/21 sec, 27/22 -- etc. Presumably the longer period is "on" since it decreases up to the steady point of 25/25.
What does this tell you?

Btw, today's "roast" reached full city (in color) in about 18 min, but without any audible cracks. Urgh.
 
renatoa
It tell me you have a lot of margin to increase temperature, assuming the 27-28/21-22 cycle is at 250 C.
Or, your real temperature is a lot lower, 230 or so... waiting to hear what the thermometer tell us.
 
Argaman
Well, I finally got my hands on a thermometer, and the results were both encouraging and confusing.

Turned to "full on" -- top and bottom elements, fan, max thermostat (250C) -- the thermometer just blew off the charts. Rose straight up to 250C, then to 300C and then just buried the needle. Extracted the thermometer so as not to risk damaging it.

In short, raw temperature production doesn't seem to be the problem -- if anything, I may have been using temperatures that are *too high*, given that I've tended to preheat the oven (and drum) to what is apparently more than 300C.

Presumably, that means the real problem is heat dispersion and, in particular, bean agitation. I'm going to have to open up the insides and check (1) the motor and (2) the fan to see what can be reasonably boosted.
 
renatoa
You measure air, right? not the radiant surface temperature...
 
Argaman
As best I could. Had to lean the probe across the rotisserie axle, trying to get the tip to stand as close the center of the oven space as I could manage.
 
Argaman
Ran another batch, same confusing results. After about 16-17 min, I hear some SC, just a few -- but still no FC. Results attached.

The thermometer doesn't go off the charts with beans in the drum, even in "full on" position. Goes up slowly from about 220 to about 240. Of course this temp is air (as measured on the side of the drum that's away from the fan) not beans.
Argaman attached the following image:
beans_-_mar_15_2019.jpg
 
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