Coffee roasting is a creative art: The alchemy of transforming fresh green coffee beans into a sensory joy. Like all crafts, roasting coffee can be exacting and precise, using high ticket coffee roasting equipment or it can be rough and dirty, with a simple, heavy-pan on the stove top. Many home roasters tend to be somewhere inbetween, maybe using a hot-air-popcorn popper or a roaster more suitable for the domestic setting.
This guide is intended to give you the necessary information for you to roast at home, no matter how you intend to roast your beans or what your skill level. However, roasting coffee varies so wildly; depending on roasting methods, bean types, environmental factors, that we have deliberately not given you a step by step recipe guide. Coffee roasting is really fun, it is necessarily experimental (we should point out that it's a lot more scientific in our roastery, but that has come from years of experience), you will probably burn a few beans along the way, maybe even some fingers*. The important thing is to play and experiment, this isn't science it's art. Have fun!
The technique itself, from starting with green coffee beans and turning them brown is straightforward. Perfecting the skill however, will require close attention to fine details through the roast, particularly near the end point.
There are several ways to roast coffee and the method you select will depend upon how much you want to spend on equipment and the amount of coffee you want to roast.
Domestic oven or stove top popcorn popper
One of the simplest ways to start is to place a layer of beans on a baking tray and roast them in the oven. This will take around 15-20 minutes. Stove top popcorn poppers can also be a good option for home roasting because they roast a larger batch and provide more control of temperature. They allow for you to adjust the gas flame and agitate the coffee beans by cranking the handle. This results in a more even roast colour.
Domestic roasting equipment
A purpose built home coffee roaster will provide the options to have even more control of the progress of the roast. Some machines give good temperature control, air flow and collection of chaff (the papery woodchip material released from the bean during roasting). This equipment will create the most consistent roast, with even colouration on the bean surface, without scorching or tipping (burn marks on the bean tips).
Our recommendation is to select beans that will show significant differences in taste. So choose beans from different countries and different post-harvest processing techniques. Learning major differences in flavour will be more obvious if you take this approach.
Learning to recognise the progression of the roast and the different stages is the next step towards taking control of flavour development. In essence different roast profiles will create different flavours in the cup.
The Stages you can expect to see (and hear):
1. Colour Change
For the first few minutes the beans will remain green but will gradually transform after that to a peanut colour; light yellow/gold. You should also notice aromas of grass and hay.
2. First crack
At this second stage the bean surface dries out and becomes wrinkled. You should notice that steam rises from the beans and produces fragrant baking and toast aromas. Around this point you will hear the sound of the "first crack". It's an is an audible crackle/pop noise. This is when roasting becomes exciting. Here sugars start to caramelise, water escapes in the form of water vapour and steam causes the cell structure of the bean to break open
At this point you can consider the roast complete. You will have a perfectly drinkable coffee with a light roast. Experimenting beyond this stage will give you variation in style and will allow you to create a flavour profile to your tastes.
3. Caramelisation
If you choose to continue roasting after this point the heat input will cause the oils to migrate to the surface. Each bean expands as the roast colour darkens. As the roast progresses to the verge of "second crack" we would recommend this as a good place to stop.
4. Second crack
Once you have reached the desired colour and degree of roast pour the beans into a metal colander and blow on them to remove any remaining chaff. It's important to know there is latent heat held in the beans, so they will continue to roast once you have removed them from the heat source (much like an omelette will continue to cook after it's removed from a frying pan). So try to remove the beans from the heat a tad before they are at your desired roast. It can take a few attempts to get this right.
Once you have reached the desired colour and degree of roast pour the beans into a metal colander and blow on them to remove any remaining chaff. It's important to know there is latent heat held in the beans, so they will continue to roast once you have removed them from the heat source (much like an omelette will continue to cook after it's removed from a frying pan). So try to remove the beans from the heat a tad before they are at your desired roast. It can take a few attempts to get this right.
Once your beans are completely cooled to an ambient temperature we recommend you store your coffee in an airtight container. We also recommend you allow the coffee to vent (de-gas carbon dioxide) overnight before sealing. Always keep your roasted coffee in a cool, dry environment and away from direct sunlight. Your beans will keep for up to 6 weeks when stored like this. Similarly you should store your green (unroasted) coffee under the same conditions. It will keep for up to 6 months.
When to start enjoying your coffee will depend on how you to intend to brew it (you can find a handy guide on how to brew here). Peak flavours will emerge overnight for filter brewing. But if you prefer to drink espresso, allow several days degassing before preparing your shots.
Good luck and enjoy experimenting!