We believe coffee roasting is a unique skill that is easy to pick up, but takes years to master. Thankfully we have been roasting for years, and that’s why we call our talented coffee roasters “roastmasters”.

We don’t rely on automated machinery to roast our coffee to perfection, instead we control the development of the roast by hand, using sensory skills to monitor changes in colour, aroma, and physical changes in the beans. The ability to craft roast to produce an accurate roast profile (how the temperature changes during roasting), is key to the consistency of each batch of coffee we roast. We also cup (taste) every single batch of coffee post-roast for quality-approval before it’s sent out to you.

We work with many different coffees; grown at varying degrees of altitudes, with a multitude of varieties, different bean densities, and crafted with different post-harvest processing methods. This means each coffee requires a specific roast profile to achieve a balanced expression of flavour. Add to this the seasonal weather changes and our roastmasters are presented with a series of questions when approaching our daily production roasts.

Whether we’re roasting on our Loring Roaster or our 50-year-old vintage Probat, every roast is approached with the same care and attention.

So how exactly do we turn our coffee beans from green to brown and what magic happens inside the roaster? Read on to find out!

Stage One - drying out and heating the beans

In stage one we aim to dry out the beans and build their core temperature – known as heat energy – so that it can be released later in the roasting process as part of the “first crack”. In order to create this heat energy we use a lot of power to start off with so the beans start gaining heat more quickly. By storing heat in the beans early on, we reduce the need to add further heat in stage two, without the fear of the temperature dropping and the roast stalling.

Stage two – first colour change and caramelised sugar

Once the first change in colour has happened and the beans have gone from green to yellow, we reduce the heat in the roasting drum to allow the carbohydrates in the coffee beans to start developing into sugars. Also prevalent when baking bread or roasting nuts, the Maillard reaction is a chemical process that occurs at 155C and results in a browning of the bean. At this point, we gradually increase the temperature of the drum to allow the natural flavours of the bean to develop. The greater the density of the bean structure, the more time and heat is required at this stage. We typically look to encourage flavours of sugar caramelising at this stage; caramel, toffee, brown sugar and chocolate.

We work hard to avoid a "rollercoast roast", where temperatures dip, or even stall. If this happens, it halts the development of carbohydrate into sugar and undesirable chemical reactions occur producing flavours you wouldn’t want in a coffee – a salty, flat, flavourless taste. Again the skill of our roastmasters is key here. Not only do they constantly watch the beans, they also use their senses to detect the point when sweet aromas change to bread-like. This is the point the coffee aromas move from hay-like to sweet roasted peanuts and we know it’s time to switch to the next stage.

Stage three – maintaining the perfect temperature

At this point we reduce the heat going into the roasting drum so we just maintain a gradual increase in temperature. This is carefully balanced against preventing the roast from stalling. If stages one and two are done right, there should be enough heat contained in the beans themselves that they can actually start their own little chain reaction of explosions to keep the roast going.

If you miscalculate the early stages of roasting, it has an impact on the final product. If continued heat is applied you can still produce a coffee that’s the right colour but the cell walls of the beans will be carbonised. This carbonisation produces a ‘roasty’, flat and burnt flavour that’s very noticeable in the cup – even if the colour of the beans appears correct.

When coffee is roasted perfectly, the physical appearance of the beans will change during the roast – the beans will expand in size and any wrinkles on the surface will be smoothed out. The beans will also crack open as they explode like popcorn. This is caused by the increase in pressure as water vapour ruptures the cellular structure of the coffee and the natural oils in the bean reach critical mass and move to the outer surface. It’s these oils that contribute to the overall flavour of the drink. This stage in the roast causes the fruity notes in the coffee which are delicate and can be destroyed if too much heat is applied initially. The key is getting the heat balance just right so the fruity notes are balanced and complemented by the sugar browning in stage two.

It is important to cup each roast and adjust the profile where necessary. Through this process we discovered our Gajah Mountain is best developed a little longer as it has some wonderful dried cherry and spice notes which only emerge when roasted with a longer stage one and two. Only then do we get the lovely stewed fruit notes and depth of flavour which we’re aiming to bring out in the espresso shot. It’s these later stages of the roast, where the body and sensation of mouthfeel are created. And here we perceive the sense of sweetness and balance that we can modify. Again, our Roasters are using all their senses, not just looking for the right colour, but are aware of the aromas produced from the beans and time taken during the roast. We continually check the beans via the small trier, pulling a small sample of beans from the drum. All these factors are being judged right up until the point that our roaster lifts the door lever and drops the beans into the cooling tray.

Throughout the roast progression, our roasters are continuously anticipating what the coffee is going to be doing, as well as what the beans are actually doing at that moment. Our roasters are always looking ahead, using the rate of temperature change as a guide to predict what will happen at later stages in the roast. We like to compare this to a conductor of an orchestra who is three strokes ahead of the musicians; our roasters are acting ahead of what the beans are actually doing, capable of dialling down the temperature if necessary, or adding slight increases of the gas if they predict the roast needs greater impetus.

The different stages of the roast, expressed as temperature against time create the “roast profile’ and we can record this data using Cropster software. This system plots the shape of the roast profile and helps us manage the roasting process by creating a picture of the reactions in the roasting drum. It is very helpful because we can see not just temperature and time, but the rate of change and allows us to refer back to particularly noteworthy roasts and identify how these were created according to the roast profile.

It is important to develop the sensory skills which relate to how different roast profiles influence the cup. Our coffees are produced against different roast profiles. Our roaster knows from experience, which roast profile will be suitable. High- dense-bean, Pico Alto Tarrazu Honey from Costa Rica, for example requires a lot of heat for development and can give the impression of being a darker roast than it actually is; due to sugar caramelization on the bean surface. But for a lower profile for a lower density profile such as Bobolink from Brazil where the roast would be more cooler and more gentle with heat application during stage one and two.

The local weather conditions in the roastery must be also given consideration when roasting coffee. On a cold day we know that a coffee might roast faster. Hit the first colour change and first crack earlier. Or on a hot moist sunny day the roast might be slower as it takes longer for the moisture to be driven from the beans, which in turn affects the later stages of the profile and delays the different points of the profile.

We design our specific roast profiles tailored to the post-harvest processes and thereby highlight these different flavours. We seek to bring out the wild strawberry fruits of a natural coffee, jammy redcurrant, sugar cane and brown sugars of the honey process, or the vanilla, chocolate and caramel and fudge of the fully washed process coffees.

A roast profile taking a shorter time, with high temperature input and full air circulation open until first crack, might bring out more fruit flavours and acidity. Whilst greater heat input in stage two can develop more body and sweetness. Longer roast times with more consistent heat application throughout stage one and two will mute the fruit notes of a highly fruited coffee and create darker, bolder flavours like dark chocolate, treacle, chocolate brownie flavours and remain very sweet with little or no fruit but a long bold aftertaste. This roast is very suited to milk-based drinks.

The coffee's origin is also important as it can guide how it might perform in the roaster drum. Traditionally, roasters have approached coffee solely by region or origin basis. However, as the specialty coffee industry has progressed and evolved, regions have started to become less significant and roasters are now looking at aspects such as varietal, process, altitude more frequently and crafting the roast on these terms rather than specifically on a country of origin basis.

Variety is another value to consider. To name just a few; Bourbon, Typica, Caturra and Catuai for example can take quite a lot of heat. Whilst Geisha, Eugenioides and Mokka are more delicate and can lose their fruit flavour characteristics easily if exposed to high levels of heat.

The flavour and taste of all coffee beans are defined by the agronomy conditions at the farm, processing and the skill of the pickers, farmers, Co-operatives and mill facility. But as the roaster, we have a pivotal role to play in the journey of the coffee bean from the farm to the consumer. We impart our personality into the coffee through the way we roast the beans. It is the skill of our roasters, gained through years of experience which enable the flavours and taste sensations to be created.

The ability to continually reproduce an accurate roast profile is key to the consistency of our coffee. Having a solid understanding of the different process techniques, origins, bean densities and varietals is key to maintaining the artisanal craft of roasting coffee, and producing unique, exciting and balanced results batch after batch.