I reached some limitations with my severin popcorn based coffee roaster trying to roast bigger batches. I found that increasing the airflow was simple enough: prizing open the vents a little at the bottom of the chamber makes a big difference. Unfortunately increasing the heat was trickier: I put a metal bin over the top of he whole unit which caused the hot air to recirculate. After a bunch of successful roasts the fan gave out and melted.

I’ve built a new roaster based on various ideas stolen from forum.homeroasters.org and some youtube videos. The design is basically along the lines of this fluid bed roaster, but everything is push-fit rather than welded. (more like jammed-together-fit).

Basically it’s a vacuum blower jammed into the back of a heatgun element to generate hot air flow. The roasting chamber is a glass candle chimney tube pushed into a cocktail shaker lid. The chaff collector is made from a tin plant pot and a stainless steel washing up scourer.

I thought I’d post some pictures and details because I’ve enjoyed looking at (and copying) pictures of other people’s coffee roaster builds.

roasting setup

Component list

The main bits are:

componentprice (uk)from
Borosilicate glass candle chimney 75mm x 152mm16.00amazon
Von haus 2kw heat gun22.99amazon
ferm 400w dust blower29.99amazon
Metal mesh9.99 (I overpaid!)amazon
hose pipe from old henry vacuummaybe 10 quid to buy off ebay as spares(actually free because I had a knackered henry)
Lid from a cocktail shaker10?(actually free because I butchered one we already had)
Aluminium tape (heat proof to 250c)5.49amazon
Voltage dimmer6.99amazon

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(amazon links are just basic links, not affiliate. I don’t get any money from these)

Details

Vacuum blower + Heatgun

I bought the heatgun first and then put everything else together around that. Unfortunately the fan in the heatgun isn’t powerful enough to loft beans on its own so I got the vacuum blower.

(I got that specific blower model because I read that somebody in the homeroasters forum had already tried it and said it was plenty powerful. A cheaper model might be just as good)

I unscrewed the heatgun and cut the fan out. I found that the hole left in the bottom was a perfect fit for a henry vacuum hose.

hole_in_heatgun

heat_gun_vacuum_mod

Although the pictures at the top of the post show a clamp stand being used to hold the thing together, the heatgun housing will actually stand up by itself. For a short while I was roasting using that with the roasting chamber balanced on top.

heat gun as roaster stand

Heating element

I used a multimeter and the voltage controller to figure out which heater wires to plug the power into. (It’s the red and white wire!)

heating_element

Heatgun barrel back together again:

heatgun_barrel

Roasting chamber

The roasting chamber is a cocktail shaker lid + some wire mesh + glass candle holder tube. The original holes in the bottom of the cocktail shaker lid wouldn’t let enough airflow through so I cut them out completely. I pushed in a circle of wire mesh.

roast_chamber_base

The borosilicate glass tube doesn’t fit at all snugy into the cocktail lid, so I used a rubber seal from a kilner jar to wedge it in a bit. I was a bit worried about the the rubber seal not being heat proof, but it doesn’t seem to matter.

roast_chamber

Voltage Dimmer / Controller

For manual control I used the same cheap AC voltage dimmer I had previous used for manually controlling the popcorn maker heater. This thing has been so useful I put a plug socket on it to make it easier to connect/disconnect, and earthed the casing.

voltage_controller

Thoughts and some stuff I missed

  • The blower is plenty powerful but is a bit loud if I’m honest. Ideally I’d like to figure out a way to make it quieter. Maybe at some point I’ll experiment with an EDF fan or something.

  • I’ve ordered a longer glass chamber (254mm). I think the 75mm width I chose was good, but it would be nice to have the option of roasting a much larger batch - e.g. half kilo and up. The fan and heating element seem to have lots of room for growth.

  • Although I didn’t mention it here, I now have it hooked up to Artisan via an arduino, theromocouple breakout and ssr. Getting a pid driven ROR curve smooth is a mission in itself so will hopefully write some more about this soon

  • I also haven’t written here about the chaff collector. It turns out stainless steel scourers make a really good filter. I ought to post some pictures of that. *Update: posted here *