One day they were out of roasted beans....but they still had unroasted, green beans. The shop owner told me that no Ethiopian would buy roasted coffee as they all did it at home themselves, in a pan on the fire.
I though to give it a try....
Update: Click here for an improvement of this coffee roaster.
Step 1: Basic on Coffee Roasting
-Roasting in a pan is not optimal; it is tiring and gives a lot of mess.
-Massive amounts of information on DIY coffee roasting can be found online, including many different devices.
The most popular DIY coffee roaster is based on a popcorn machine. When I came across one in a shop for 10 euro's I decided to try to make a coffee roaster myself. I got all information online, but didn't come across a full plan explaining how to make one that really works, so here is my contribution.
(While writing this, I just crossed page with an unbelievable selection of DIY coffee roasters, many fully controlled. Just have a look here yourself.)
Step 2: Making the Popcorn Machine Into a Coffee Roaster
I started with this link, but I found out that my popcorn machine didn't roast the beans. It hardly popped popcorn. Then I found out it didn't heat above 180C (that's probably why it was only 10 euros).
I opened the roaster and bypassed the heating security (as I didn't take any pictures during the making of the coffee roaster, you need to check the site below for details on bypassing the security). Without this security, your roaster could go to higher temperature than it is supposed to, which could result in fire. So be smart. I noticed this already when the see-through polycarbonate cap started to meld. Therefore I replace it with a food tin, with bottom and top removed.
With the security bypassed, the popcorn machine could heat up to higher temperature, but still not high enough. Then I came across this website and followed the advice to disconnect the fan and the heating coil and make the fan speed control-able. As I don't understand too much of electronics, it took me a while to find out how to do this (the dimmer mentioned on the site cannot work, as far as I know). The motor in my popcorn machine requires 20V and uses about 0.8A. You can't simply reduce the voltage as the motor will not have enough power to keep on going at lower voltage. Instead you will need a pulse-width modulator. I got a DC motor speed regulator (Kemo electronic B71) for 20 euro, which I needed to put together myself, but worked perfectly. As a power source, I use the adapter of my laptop (19V 3.4A).
Disconnecting the coil and fan allows you to turn of the coil at the end and cool your beans with the fan at max, which is also great compared to cooling the hot beans in a colander.
Next, you need a good thermometer! Mine is a cooking thermometer, going up to 300C. You could do without, but you will not be able to follow a temperature profile and it will be difficult to repeat your results as the outside temperature is of great influence to the temperature in the roaster. Mine cost me 40 euro, which I realize is a lot of money. But with this, your coffee roaster will be much more advanced than the commercial roasters you can buy for 200 euro's, which doesn't measure temperature, only time.
Drill a hole through the popcorn machine and into the aluminium tin and place the temperature sensor about 1 cm above the bottom of the tin.
Step 3: Roasting Beans
Initially I though you just needed to roast the beans until you reached your preferred temperature/roasting degree and then you were fine. I tried this and didn't get satisfying results. One time I roasted till 220C and got little carbonized beans.
I came across a site which mentioned the use of a temperature profile. I lost the link, but it looked a bit like this:
-Heat up to 150C and keep it there for 1 minute.
-Heat up to 190C with about 13C/min
-Keep it at 190C for 1 minute
-Heat up with 3C/minute until you reach your preferred temperature.
I tried this profile now twice, heating up till 208-210C and am very satisfied with the end result.
To roast you will be needing:
-Fresh coffee beans
-A good thermometer, going up to at least 230C
Put the thermometer in the roaster and fill it with 100g of fresh beans. Turn on the ventilator at max and then turn on the heating coil (always have the fan running when the heating coil is on!!). Make a temperature note every minute. After you reach 150C, control the temperature for 1 minute by fan speed and turning the coil off and on (requires a bit of practice).
Then, heat slowly up to 190C in 3 minutes, keep it there for one minute and then go slowly (3C per minute) to you desired end temperature. Once you reached that, you turn off the coil and put the fan on max untill the beans are below 80C, which takes a few more minutes.
Controlling the temperature is quite difficult, but if you try it as best as possible, you will end up with a nice result. It is important you keep your beans dancing. If the fan speed is to low, the beans will stop and you might get an uneven roasting, of even burn the ones at the bottom . If you can't get the temperature to rise anymore without the beans stop dancing, you need to use less beans or find alternative methods, like putting a cap on the tin or recirculating a part of the warm air.
As adviced, I let the beans stand for 1-2 days before I use them. They would degass during this period, although I never tested if you can drink coffee direclty after roasting the beans.