Basically it’s a baked-bean can with both ends taken off, with a jam jar jammed into the top end and vents cut in the side.
The can is then put inside a tin plant pot with a hole in the bottom and a couple of steel scourers are wedged around the jar to hold it in place and filter the exhaust.
The idea is that the chaff gets blown up through the bottom and out into the pot via the vents. The vents are cut and pried open so as to rotate the air in a sort of cyclone. The chaff then settles at the bottom of the collector in between the tin and the pot and the steel scourers stop any chaff escaping out the top. Every so often I empty the chaff out by lifting out one of the scourers:
It works a lot better than I expected, removing all of the chaff and pretty much all of the smoke from the exhaust. It was instrumental in allowing me to move the roaster from outside to inside the house.
I guess the jam jar isn’t strictly necessary. I originally put it there to provide a way of looking into the roasting chamber on my old popcorn roaster, but it was never very effective for that purpose. The advantage it provides is actually the weight it adds to the collector.
Below is a picture of the base of the plant pot just prior to cutting. I cut between the small holes so there was a hole big enough to wedge the baked bean can through. If I was to do it again I’d make the hole smaller and just sit the can+jar in the pot.
This particular tin plant pot has a nice lip at the bottom which makes it easy to sit on a circular roasting chamber. The weight of the jar is enough to stop the collector moving or blowing off because the scourers provide surprisingly little air resistance for the filtering they do, and they don’t seem to get bunged up with chaff. If the collector needed more weight I could put something in the jar to weigh it down, but this hasn’t been necessary even with my new 400w blower on full power.
I can’t really take credit for the design as I think I pinched it from a youtube video a while back. If I remember correctly there was a retired gentleman showing off his popcorn roaster and it included this design or something like it. I haven’t got the link now, please let me know if you see it and I’ll give him full credit.
Update! I think it was this video featuring somebody called ‘Chicago John’, although his collector is a bit more sophisticated than I remember! Thanks John!
Anyway, here’s a picture of my roaster in its latest incarnation: I now have the longer borosilicate roasting chamber I mentioned at the end of the previous post and I’ve also attached aluminium ducting to another tin pot so that it can sit on top of the chaff collector and vent the remaining fumes during first crack.