This is just a little insight into the roasting process. We love that we have control over this and therefore what ends up in your cup, we hope you do too...
Specialty coffee roasters work with great quality green beans. There are various types, the most common being Robusta - used more in commodity coffee and Arabica - seen in most specialty coffee shops.
The cherries (see first picture above)are picked on the farm, whether from Brazil, El Salvador or Bolivia to name a few. On the farm they are then treated, this could be naturally dried or washed to get the green bean. This is an important step and there are a few methods. Even the altitude at which beans are grown affect the end product as those at higher altitude are more dense, therefore the roasting and in turn the flavour can be different. Each of these steps are also worth looking into and learning about if you are interested in detail, and what differences in each step the coffee goes through changes the end product that you taste in your cup.
So for the actual roasting process:
The green beans are put into the roaster once it reaches desired temperature (for example 190℃). The bean then goes through its drying phase, making the roasting chamber quite moist for the first couple of mminutes. This is a good time to add maximum heat. Moist air has higher heat capacity and it will also be more gentle on the bean surface. What we don't want is a bean burnt on the outside and untouched in the centre. Once the bean has dried out it will start to generate heat beacause of combustion. The bean will start changing colour by starting to brown and around now you will hear the first pop (also know as the first crack), it will also begin to swell because of the generation of vapour and CO2. This stage the flame will also need to be turned down so as to control the temperature and reduce the speed the bean roasts. Again this is in order to make sure the bean is cooked correctly. The internal bean heat will then do the roasting while the air temperature in the drum will help maintain the bean temperature. From here on the temperature will steadily rise as the bean roasts and the roaster will be keeping an eye on the colour of the bean. The bean will go through various key stages as it gets darker. Often lighter roaster beans are used in brew methods such as aeropress and chemex. This is because it can be a good stage to bring out the acidic flavours and lighter floral notes. Plus many others. While darker roaster beans lend themselves more for an espresso, with the rich, bitter earthier flavours and fuller body. So visually the colour is important but as it gets darker you will also hear a second crack. Most beans have already been taken out by now but sometimes roasting this long can produce agood flavour particularly for espressos. As the roasting process goes on longer oils will start to come out. If you go in certain coffee shops you can see this. A dark, glistening bean in the grinder. These can be delicious but also often too bitter and have lost all the other delicious flavours that make coffe amazing and unique.
Essentially coffee roasting is about caramalising the bean bringing out its natural, beautiful flavours. You want the sugar element to come out as expected from caramilasition, but also with coffee it is of course the bitter element. However with all great food and drink it is the balance so there is still the acidity and sour flavour to think about and each bean may be used for its particular characteristics. It is the roasters job to ensure they treat the bean in order to best bring this out. So whether it needs to be lighter roasted which will lend itself well to a filter type coffee, or perhaps darker roasted for a fuller, creamier espresso, each step is important and this roasting step is one of those. It takes practise and experimenting and plenty of tasting!