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:

component price (uk) from
Borosilicate glass candle chimney 75mm x 152mm 16.00 amazon
Von haus 2kw heat gun 22.99 amazon
ferm 400w dust blower 29.99 amazon
Metal mesh 9.99 (I overpaid!) amazon
hose pipe from old henry vacuum maybe 10 quid to buy off ebay as spares (actually free because I had a knackered henry)
Lid from a cocktail shaker 10? (actually free because I butchered one we already had)
Aluminium tape (heat proof to 250c) 5.49 amazon
Voltage dimmer 6.99 amazon

(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 *

JX Pro david@bellabarista.co.uk