Coffee Roasting: A Guide to Roasting Coffee Beans

Having enjoyed freshly-brewed coffee for many years, I thought I would have a go at roasting my own beans. There are several ways to this including simply baking on a tray in a hot oven. However, I wanted a method that was a bit more predictable and repeatable so plumped for a slightly more ‘high tech’ option. I bought this roaster from Amazon though other suppliers are available. This machine is also great for roasting peanuts, pecans, hazelnuts, etc. It will probably do popcorn and is very easy to clean thanks to its ‘teflon’ lining.

I get my green coffee beans from Rave Coffee; they have a good selection at reasonable prices. A while ago I suggested they include roasting suggestions (e.g. medium or high roast) and flavour notes with their green beans and I’m glad to say they now do.

I roast 500g batches of green beans; sufficient to last me about two weeks (one large cafetiere/day). Yesterday, I roasted some Sumatra Mandheling beans using my standard operating procedure (SOP).

First, set up roaster outside because it can generate quite a bit of ‘smoke’ depending on the type of beans. Pour the green beans into the roaster, replace the lid, set the temperature to 200°C, switch on and start the stopwatch.

After 10 minutes, increase the temperature to maximum (240+ °C) for a further 10 minutes. Note: I have measured the ‘actual’ roasting temperatures with an infra-red thermometer and find they are about 20°C below the marked temperatures in this particular roaster.

At around 20 minutes, you can hear the ‘second crack’ - at this stage, you have a medium roast coffee; my preference because it brings out the individual flavours of beans from the different sources and processing methods used to prepare the green beans.

Roast for another 1-3 minutes for a ‘medium-high roast’ or 4-5 minutes for a ‘high-roast’ though timings will vary depending on the machine. For high-roast, the coffee beans will become oily as well as darker. Part of the fun is experimenting with different roasting temperatures and times.
As soon as you have the degree of roast you want, you need to cool the beans as fast as you can to prevent ‘overcooking’. I do this by transferring the hot beans to a colander and then removing the ‘chaff’ by pouring the beans from one colander to another; a gentle breeze helps.

The roasted beans are left to cool before transferring to airtight containers. I’ve been told that some ‘outgassing’ from the roasted beans may occur but I’ve never found this to be an issue. To be on the safe side, you might want to leave the lid off the airtight container overnight and/or periodically open and shut the container.

Final Product

The roasted beans are not a uniform colour, thought this variability is less for high-roast coffee beans, due to inefficient mixing and uneven heating in this particular roaster. I quite like this quirk because it results in more complex tastes and flavours and every pot of coffee is different. These Sumatra Mandheling beans resulted in an earthy, spicy taste with a hint of fruitiness (I couldn’t tell you which fruit though!).  

Coffee from freshly-roasted beans is far superior to anything bought from your local supermarket though it can be a little more expensive. Ideally, roasted coffee beans should be ‘drunk’ within a week for the very best flavour. If you like coffee and enjoy trying something new then why not give it a try.


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