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 Even roasting with a popper
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| marcov |
Posted on 03/22/2019 1:25 PM
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 1/4 Pounder  Posts: 61 Joined: January 21, 2019 |
Hey, I have so far done a handful of roasts with my modified popcorn popper. One of the thing I'd like to improve is roasting evenness. I'm running the popper with 50g of beans, and beans seems to rotate well enough since the charge phase. However when done not all of the beans are of the same colors, and some of them are colored like hazelnut shells. I'm trying to understand why. Could it be that the vortex generated by the basket shape forces the beans to always stay at the same height? What have you done on your popper to achieve a more even color? |
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| JitterzZ |
Posted on 03/22/2019 7:19 PM
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 1/4 Pounder Posts: 151 Joined: October 08, 2018 |
Stir Stir Stir. With a popper, you're not roasting properly if you're not covered in chaff and if your stir hand doesn't feel like it's about to ignite. |
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| Wiz Kalita |
Posted on 03/23/2019 4:05 AM
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Newbie  Posts: 49 Joined: August 06, 2018 |
I run 130 gram batches, never stir manually and I always keep the fan on full. I find that if you don't use enough beans to cover the slits, most of the air is just going above the bean pile rather than through and you don't get good agitation. It might sound counter intuitive but I got more consistent roasts and better heat retention when I increased the load. |
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| renatoa |
Posted on 03/23/2019 4:31 AM
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Administrator  Posts: 3005 Joined: September 30, 2016 |
Rotating is not enough, if no ascending movement too, then the bottom beans will always get more heat than the upper beans. So you need to disrupt somewhat the vortex, either stir, either by whatever asymmetry... for example try leaning the popper on any side, to see what nice fountain will build on the wall, or bending the hot air admission gaps, to have more airflow in a side than in the other. |
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| marcov |
Posted on 03/31/2019 4:41 PM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
So I followed your suggestions. I changed the shape of the vents in the basket with some ?brute force? :-) and now I can see some ascending movement too. I boosted the dc voltage too, by maxing out the voltage tuning screw of the power supply. I can see more consistency now.... However, I am struggling to provide enough heat to complete a roast at 200C, no matter how many beans I put into. I am considering shorting the secondary heating element (the one used originally to supply the fan), so that the primary can get the full mains voltage. Any strong opinion against it? I know it will shorten its life, but it is under ssr control so not working at 100% most of the time. |
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| Wiz Kalita |
Posted on 04/01/2019 12:55 AM
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Newbie Posts: 49 Joined: August 06, 2018 |
A larger batch size will also help with heat retention because it slows down the airflow. Also, I have a tea basket on top of my funnel to catch chaff, that slows down the airflow too. EDIT: Rewiring your coils to increase power above the factory specs can be dangerous. Edited by Wiz Kalita on 04/01/2019 6:37 AM |
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| renatoa |
Posted on 04/01/2019 2:05 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
BEWARE! Wiz Kalita suggestion has a fire hazard, not working for all poppers ! There are poppers where coils are serial, and the motor coil is designed for 19V, and models where motor and heater circuits are parallel and separate, and motor coil is designed for mains voltage. The above suggestion works for the later case only, and brings some 100-200W more power, depending on mains voltage. Attempting this solution on a serial circuit will led to a massive overpowering of the motor coil, enough to make it blow. Will act asa fuse, but not instant, will take some seconds, enough to risk a fire... |
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| marcov |
Posted on 04/01/2019 2:21 AM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
That's exactly why I am asking this. My heater coil is 41 ohms, in series to a 7 ohms coil. That is probably calibrated to act as a voltage divider to generate 20VDC for the fan. I am now planning to have 230V on the 41 ohms coil, that means about 20% more current. |
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| renatoa |
Posted on 04/01/2019 3:10 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
17% say my math, thus 36% more power. Not sure why you would need so much power, as I remember when I was in the "popper age" , 50% was been enough for dry phase, i.e. reaching 150 CMaybe your probe is not reading well those 200 C... do you have FC within 9-10 minutes ? this is what matter more than a - possible fake - temperature reading. |
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| marcov |
Posted on 04/01/2019 4:17 AM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
To be honest I am struggling to hear FC most of the times. My roast time are around 13-14 minutes for a City+ (or a tad ligher). I compared my BT accuracy with a cooking thermometer, and there is a difference of max 15C (with TC measuring the lower). I am attaching a recent roast I did, you can clearly see that heater saturates at 100% and I am forced to reduce fan speed to compensate.
marcov attached the following image:
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| Wiz Kalita |
Posted on 04/01/2019 6:37 AM
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Newbie Posts: 49 Joined: August 06, 2018 |
Quote Good point, thanks for correcting me. I have edited my post. |
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| renatoa |
Posted on 04/01/2019 6:48 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
Quote marcov wrote: ...you can clearly see that heater saturates at 100% and I am forced to reduce fan speed to compensate. This is the part where I would investigate more, not heard from others or remember in my experiments to push THAT hard the power in a popper.  And the proof something isn't right is the way how a brand new bought and unpacked popper behave if you try to roast coffee without any mod: you have FC by minute 3-4 and charcoal in 6 minutes |
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| marcov |
Posted on 04/02/2019 7:58 AM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
Yeah that?s a good point I chickened what?s the actual power consumption of my machine with the heater 100% on and it?s about 1850w. So if the power is OK, the temperature is OK, then maybe my problem is that my basket top is too open and all the heat is going away. At the moment I am using a rudimentary chimney built with some tick aluminum foil... that?s the max carpentery my fractured wrist allows me for now I prolly have to design and build something better. |
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| Wiz Kalita |
Posted on 04/02/2019 8:44 AM
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Newbie Posts: 49 Joined: August 06, 2018 |
1850 W is 650 W more than mine, so you should be good. My chimney is made from a metal tube that I sourced from the juice shelf of the supermarket, opened with a can opener and attached to the popper with high temperature mounting glue. You should make sure there aren't any sensitive coatings that will release nasty fumes, of course. |
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| renatoa |
Posted on 04/02/2019 9:36 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
I am concerned where all this power is going though... |
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| marcov |
Posted on 04/03/2019 9:25 AM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
it's for sure turned into hear :-), but probably in a quite inefficient way. I am anyway surprised of how a popper rated 1200W is absorbing 600W more. |
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| renatoa |
Posted on 04/03/2019 10:27 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
... and "absorbing" without bursting into flames... |
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| Wiz Kalita |
Posted on 04/04/2019 2:41 AM
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Newbie Posts: 49 Joined: August 06, 2018 |
Looking at your old posts it seems we have the exact same model, so I guess we have the same amount of power too. In my roaster, failure to reach temperature means there's a leak somewhere. If hot air is coming out the wrong holes, you're wasting energy. |
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| marcov |
Posted on 04/05/2019 3:00 PM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
Quote Wiz Kalita wrote: I run 130 gram batches, never stir manually and I always keep the fan on full. I find that if you don't use enough beans to cover the slits, most of the air is just going above the bean pile rather than through and you don't get good agitation. It might sound counter intuitive but I got more consistent roasts and better heat retention when I increased the load. So you are using the Severin PC 3751 popper,with 130g batches and dont need to stir? Wow. I should try this too. |
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| renatoa |
Posted on 08/08/2019 6:54 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
I started with a popper and abandoned it in some months. The roast chamber is too small to have a good beans movement, even with stirring. The beans turn, but there is no ascending and descending forces, as a result the bottom beans will roast quicker than the top beans. There could be some fixes, consisting mainly in destroying the symmetry of the vortex, as covering some bottom air slots, or lean the machine from vertical, but all require very fine tuning to obtain a "fountain", and roast aren't reproducible for different weight or beans density. There are some cheap commercial roasters, as the SR line, Nesco, or Dieckmann Roestmeister, that could give you better roasts than a modded popper. Or, build yourself a flour sifter/hotgun machine, requires similar skills and tools as modding a popcorn and the results are better, imo. Edited by renatoa on 08/08/2019 7:17 AM |
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| snwcmpr |
Posted on 08/08/2019 8:15 AM
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 1 1/2 Pounder  Posts: 925 Joined: March 03, 2011 |
Too many beans are usually the cause, in my experience. Only add enough beans that they are 'just slightly' moving at the start. That will ensure enough movement during the roast.
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Backwoods Roaster "I wish I could taste as well as I wish I could roast." As Abraham Lincoln said "Do not trust everything you read on the internet". |
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| snwcmpr |
Posted on 08/08/2019 8:18 AM
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1 1/2 Pounder Posts: 925 Joined: March 03, 2011 |
Quote OhhEnnEmm wrote: I have a standard popcorn maker stored away in the loft. I never thought to use it for roasting coffee, since I've never actually roasted coffee... You think it might be worth me buying green beans and giving it a go? Or should I just buy pre-roasted and grind it myself? If an expert roaster has pre-roasted the beans, surely that's still better than me with my popcorn maker? Idk I'm just tryna figure the best way for me to get into all this properly. It depends on the popper model. Some cannot roast, and others rost very well. What model is your popper? --------------
Backwoods Roaster "I wish I could taste as well as I wish I could roast." As Abraham Lincoln said "Do not trust everything you read on the internet". |
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| marcov |
Posted on 08/08/2019 9:52 AM
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1/4 Pounder Posts: 61 Joined: January 21, 2019 |
Just reporting that I slightly improved evenness by modifying the roasting chamber. What I did is flatting out the vents to "close" the chamber as if it was a closed glass of aluminium, and then drilled ~7mm holes on the sideo, spaced ~7mm apart and as low as possible, but keeping the flat bottom intact. I have observed an higher air flow (probably the original vents are too small) and now beans jumps instead of rotate |
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| renatoa |
Posted on 08/08/2019 9:55 AM
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Administrator Posts: 3005 Joined: September 30, 2016 |
A video worth... more than words |
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