From Origin To Cup – Roasting

From Origin To Cup – Roasting

At the heart of what we do, we take raw, green coffee beans, and roast them. But what does it mean to take a hessian sack full of beans and transform them into something delicious? There’s something unassuming about a green bean – it doesn’t have the same standout aroma as a roasted one, and to chew on one would be nothing short of disappointing – vegetal and grassy. The magic, of course, is in the roast.

In the simplest possible terms, the roaster is where the green beans are turned brown, through application of heat. This may sound so obvious that it isn’t even worth mentioning, but with peoples’ knowledge of the coffee industry being so varied, it is often the case that we can meet someone who hasn’t just never seen a green bean, but has no idea that coffee beans are green to begin with.

The roasting process is complex, and takes an in-depth understanding of the roaster itself and the chemistry of the coffee bean to be able to consistently roast delicious coffee. As we’ve touched upon previously, coffee is a fruit, and our ultimate aim is to roast the coffee we have to heighten the sweetness of that fruit.

The same green bean can be roasting in a multitude of ways to create a variety of outcomes in the cup. The less time a coffee spends in the roaster, the lighter and more acidic it will ultimately taste; the longer spent in the roaster, the darker that same coffee will become, and the more bitter (and maybe even burnt) it will be. In this respect, roasting coffee is a lot like cooking a steak – the same cut of beef can be cooked to be rare and blushing, or to be cooked all the way through, closer to well-done. In both cases, the operator is aiming for a specific outcome, and they need to have the ability to control the process from start to finish.

Another parallel to consider is that when thinking back to beef – different cuts are suited better to being cooked in different ways, depending on their inherent qualities. A fillet steak is best suited to being carefully grilled to perfection, whereas a shin of beef needs to be left to tick away in a slow cooker to really get the best out of it. The same applies, in a sense, to coffee.

The roaster needs to consider many factors when approaching the roast. Some coffees are best suited to a lighter, quicker roast, which maximises their sweetness and acidity – many African coffees are prime examples of this. Roasting our Ethiopia Rocko Mountain, for example, we have tried a more developed roast out of curiosity, but we have always found that a lighter touch is the only way to maximise the pulpy orange notes, and hits of berry. It would be a waste of a fine coffee to take the Rocko any darker than we do. Conversely, roasting our Sumatran coffees like our Ethiopians would be disastrous – they need more of a ‘low and slow’ approach to coax out their body and complexity – lighter Sumatrans that we have tried have tasted flat and one-dimensional, so we avoid them. Each of our coffees have gone through a thorough profiling process, where we assess the quality of the roasts until we settle on an outcome which maximises the quality of that bean’s characteristics.

One huge factor that we always have at the forefront of our minds is consistency. It’s one thing to roast a coffee once and it taste great, but we need to be sure that every time we approach that coffee, we get the same outcome. We use a software called Cropster, which allows us to track the temperature of the roaster, and the beans within it, so that we know exactly what impact we’re having when we adjust the gas. Guy, our head roaster, is constantly looking into ways to utilise this software to its full potential. In Rounton Coffee B.C (Before Cropster), we took notes of the temperature displayed on the roaster itself, crossed our fingers, and hoped for the best. These days, we can do all sorts of things to achieve consistency – whether that’s following the profile of a roast on a screen connected to the roaster, or using Cropster to log our cupping scores for particular roasts; we now have the means to focus in on the smallest details so that we can continually improve. 

The Stages of the Roast


Coffee beans contain between 10 and 12% moisture. To reduce this moisture and allow the browning reaction to take place the beans must enter a hot drum – anywhere from 175 to 245°C. The dense green beans then start to absorb the heat and energy and the moisture starts to evaporate. The aroma and appearance changes very little during the drying stage.

Yellowing – the Maillard reaction

Only when the moisture levels have sufficiently dropped can the beans begin to change colour. They start to change from deep green to yellow, and a fine layer of skin or ‘chaff’ starts to separate from the beans. The chaff is extracted by air from within the roasting drum to avoid it burning, which would spoil the flavour of the coffee and potentially become a fire hazard. It is crucial that the roaster dries the coffee properly and that the yellowing stage is a relatively slow process – otherwise the coffee will roast unevenly. It could appear roasted on the surface and raw on the inside resulting in grassy and underdeveloped flavours. This process is also called the Maillard reaction, which is the same series of changes that happen in the baking of bread, or searing of a steak: the reaction of sugars, carbohydrates and amino acids that allow coffee to develop body and complexity. 

First Crack

As the coffee moves from yellow to brown, gases will develop within the beans that create pressure and ultimately the beans will pop and crackle and almost double in size – similar to how popcorn pops. Prior to first crack, the coffee is not soluble, and if ground, there would be nothing resembling a cup of coffee at the end. 

Roast Development

At this stage, the roaster needs to decide how long they want to develop the roast for. What is crucial at this stage is to reduce the heat being applied to the roaster to a minimum. Having lost all moisture, the beans are now extremely sensitive to heat, and even the slightest bit too much will run the risk of scorching the beans. However, they must also be careful not to arrest the roast too soon – beans with a temperature that reaches a plateau for too long, will create a baked, hollow cup. There is an element of experience required at this stage, to know what the coffee will likely taste like at each point in development, but the basic principles remain the same: we want our coffees to take on less and less heat as the roast comes to an end, and we want to make sure that the develop the coffee in a way that makes sense for that particular origin, processing method, and how we expect that coffee to be brewed. Development is measured as a percentage of the entire roast’s duration – we find that DTR (development time ratio) usually falls between 12-20% of the roast – that is, 12-20% of the roast is dedicated to time spent after first crack. 

Second Crack

Most specialty coffees will be released from the roasting drum at some point within the development stage. It will be air cooled in a turning tray to stop the roasting process as soon as possible and in the case of larger commercial roasting this may be aided by the addition of water which is sprayed onto the coffee.

However, there are some roasters who set out to produce very dark roasts in order to provide a style that is enjoyed in some parts of the world. They will keep the beans in the roasting drum which will now be getting much hotter. Soon the beans will start to crackle and pop again and this is known as second crack. The coffee oils will have reached the surface of the bean which will appear dark – almost black – and shiny. By now the majority of acidity and sweetness will have been converted to different flavours – predominantly ashy and bitter. Such characteristics are appreciated in much of Spain, Turkey and the south of Italy. There would be little point in roasters who roast this way using specialty coffees since at the stage of second crack, all the finer flavours and aromas will have disappeared up the roasting chimney. When roasting beyond second crack, the coffee will have to be soon released from the roasting drum or will set on fire.  At Rounton Coffee, we aren’t interested in taking our coffees to second crack. We create espresso blends that bring about plenty of body and strength but retain the sweetness and character inherent in the specialty beans we source.

Post Roasting

Once the beans have sufficiently cooled down, they are packed as soon as possible. The roasting process and the inevitable creation and release of oils means that the coffee beans now face a threat – namely oxygen! It is oxygen that reacts with oils to create peroxides – a process that leads to rancidity. The key to preserving coffee beans is to pack them into an atmosphere free of oxygen. Freshly roasted coffee emits carbon dioxide, a gas that is harmless to the flavour of coffee beans. We take advantage of this physical phenomena by allowing that aroma rich gas to fill the head space in our coffee packs. The sealed bag is fitted with a valve so that oxygen cannot enter but if the pressure in the bag becomes too great, The CO2 can escape through the valve. It allows us to give our coffee a three month shelf life.

It’s technical stuff but greatly helps us in our mission and obsession to supply our customers with the freshest coffee possible. We’re also believers in the concept of ordering little and often (rather than bulk buying). After all, there is little point in selecting beautiful, complex specialty coffees and roasting them to perfection only for oxygen to spoil all of our work. For us, freshness is everything.