Building A Handmade Roaster
To build your own coffee roaster, you’ll need some kind of man cave! A place to store all the materials and construct your design. Make it comfortable as this project is going to stretch you and take some time to complete.
(I spent about 200 hours building the roaster)
OK, so you’re all setup with tools including a welder and a sketch of what you’d like to create. Always make drawings with dimensions and then make a model to see how it will look once built. (I used some sign board material but cardboard is really good.)
Rotate a Drum
Find yourself a mild steel cylindrical object where you will fabricate one open end and the other end designed to keep beans from passing but allowing air to enter.
Centralize the drum with an axle and attach to bearings so that it turns with minimal resistance.
During the prototype stage, I used a pulley from a washing machine and an electric motor from a deli meat slicer. Although this got me going where I was able to check that the drum rotated without snagging, the drum turned too fast and had little torque. I eventually purchased a single phase motor with built in gearbox and had the gearing set to 50 RPM.
Choose a gas burner that corresponds to the size of your drum. The larger the drum, the more btu’s required to heat it. Install the burner to one side of the drum so that the heat is drawn in and around drum as it rotates. Install a baffle plate so that the heat dissipates and doesn’t overheat the drum.
Remember to insulate the drum housing so that the heat is concentrated into the drum – this is key to transferring heat energy into the bean which in turn is the catalyst of the beans flavour development.
I followed a conventional design where fresh air enters the roaster from the rear of the drum. As the air enters the roasting chamber, it heats up and the smoke and hot gases are sucked out of the chamber by a variable speed blower motor located externally. By Locating the blower motor on top of a cyclinder, one can create a cyclone. Increasing the speed of the blower motor once the coffee beans achieve 1st crack, enables moisture, smoke and chaff to be removed from the roasting drum thus creating clean, well developed roasted coffee. The removed chaff caused by the roasting cycle is efficiently removed by the blower motor and sucked into the cyclone where it spins around the wall of the cyclinder, eventually separating from the smoke and resting at the bottom of the cyclone chamber.
Measuring Time and Heat
I used two thermo couplings to monitor heat at the top and bottom of the roasting drum and called the top probe ‘air temp’ and the bottom probe ‘bean temp’. Ensure that the bean temp probe is sufficiently submerged within the bean pile during roasting. As the thermo couplings were Bluetooth enabled, I was able to connect to an iPad. Using software supplied by the manufacturer, one is able to monitor the temperature curves of both probes. For each batch of coffee, I create an identity card, recording charge temps from the air and bean probes and then use a stop watch to record the time taken for the ‘bottom out temp’ of the greens, 1st crack and drop time.