Every barista wants to learn more about roasting, I bet! Coffee can acquire flavour by being roasted. How can we make coffee that tastes the best? What exactly transpires during roasting?
Why is roasting crucial—or even necessary?
Coffee cherries ripen the seeds that become coffee beans. After processing, the dried coffee beans are produced. Coffee beans are green in colour and smell beany and grassy before roasting. Green coffee beans don’t actually smell at all like coffee. We produce 800 to 1000 different fragrance molecules when we roast coffee. These ingredients give coffee its flavour. We can change the presence of these scent components in coffee and the flavour of the coffee by using roast profiling.
Process of roasting coffee
Coffee beans are turned from green to brown during roasting. It can be prepared in a variety of ways, which changes the flavour. I’ll go through commercial roasting and roasting principles in this article. Visit Tomi’s blog to learn about the many methods for roasting coffee at home.
phases in roasting
Drying, browning, and development, or roasting, are the three primary steps of roasting.
1. DRYING STAGE
Humidity levels in coffee beans range from 8 to 12 percent. Before we begin the actual roasting, we must dry it. The drying phase of a conventional drum roaster normally lasts 4 to 8 minutes (see below for roaster designs). Usually, the temperature is 160 0C at the end of the drying stage. You must be careful while using drum roasters, in particular, to avoid burning the beans by introducing too much heat at first. Since the final roasting stage is exothermic, the drying stage is crucial for the bean’s ability to gather energy (heat producing).
2. BROWNING STAGE
The coffee begins to smell like toasted bread and hay at 160 0C. At this point, the fragrance precursors begin to transform into scent molecules. Drying continues even when the browning stage comes after the drying stage.
The Maillard process, which causes browning, begins at the browning stage. Reducing sugars and amino acids undergo the Maillard process, which produces thousands of distinct fragrance and colour chemicals called melanoids. The roast naturally slows down at this point, and some roastmasters purposefully do the same to ensure flavour development. The coffee begins to pop at the end of the browning cycle. The development stage begins at this point, which is known as the first crack.
3. ROASTING OR DEVELOPMENT STAGE
The coffee cracks at the beginning of the development stage when the reaction turns exothermic. The coffee explodes because the bean has accumulated energy during the drying and browning steps. The desired scent molecules are formed throughout this period. If we don’t slow down the roast throughout the development stage, we can easily end up with coffee that tastes excessively sharp and smokey.
Depending on the intended flavour profile and roast level, the development stage normally takes 15 to 25 percent of the entire roasting time.
One of the most crucial roast indicators is roast degree. It can be determined by tasting or using a colour metre. The main goals of roasters are to determine the roast level and improve the natural flavours of coffee. Dark roasted coffees are typically bitterer and more acidic than light roasted coffees. Additionally, fruity flavours are more prevalent in light roasts, but roasty and burnt flavours are more prevalent in dark roasts. Due to the high concentrations of the chemical component 5-hydroxymethylfurfural, light roasted coffee has a fruitier flavour. This chemical transforms into less fruity molecules as roasting progresses. As sulfuric chemicals are present in greater quantities, roasted and burnt flavours result. We can infer that light roasting brings out the flavour of the raw coffee more effectively as a rule of thumb. Dark roasted coffee is more difficult to distinguish from one another than light roasted coffee.
Time to roast
Even while the degree of roast has the greatest impact on the flavour profile of coffee, the overall roasting time and the length of each step are also significant elements. You will produce more of the desired fragrance components if you roast quickly. However, take care not to overcook the beans! The flavour of coffee as a whole—fruity, berry-like, chocolaty, and nutty—is stronger. Additionally, quick roasting produces more fragrance components, which are produced at the beginning of the development stage.
Fast roasting is not always a smart idea. The properties of coffee or roaster design may be to blame (see the sentence below this one below). Rapid roasting increases the coffee’s flavours in all ways. We must change the roast profile if we don’t want some flavours in the coffee. For instance, while acidity is typically a preferred flavour, people occasionally prefer low acidity in their espresso blends. The coffee becomes less acidic as roasting takes longer because organic acids have more chance to dissolve. When this happens, slow roasting might be a smart move.
There are various roaster layouts. The design has an impact on the thermodynamics of roasting, and different machines can produce coffee with varying flavours. Beans rotate in a drum that is cooked below using either a direct or indirect flame in small roasters most often. This increases the energy volume of roasters. These equipment make roasting more stable, but the roastmaster needs to be able to plan ahead for many minutes. Drum roasters work best when roasting slowly because starting the roast at a high temperature can cause the bean to burn on the outside. We use a Probatone 5 coffee roaster called Bertha, a conventional drum roaster, in Paulig Kulma.
Fluidized bed roasters have been around for a very long time in the industry. Hot air is used to indirectly heat the fluidized bed roaster. As a result, controlling the roaster is quicker. Fluidized bed roasters enable faster roasting without external bean scorching while also enhancing coffee aroma. Our roaster at the Vuosaari roastery is one example of a fluidized bed roaster. Additionally, there are a few hybrids between fluidized bed roasters and drum roasters, such as Loring Roasters, which include a drum but heat is only applied indirectly through hot air.
espresso or filter coffee roasting
Have you ever wondered what the actual distinction between espresso and filter coffee is? Gravity is used in the gentle process of filter extraction. You can use more acidic and very aromatic coffee for the filter. Espresso, on the other hand, is extracted under a 9 bar pressure. That indicates that more flavour is added to the cup. Coffee that is roasted for espresso may occasionally not be as delicious as filter coffee, and vice versa. Some roasters choose to roast coffee just for the bean, disregarding the extraction process, which means they strive for a perfect balance between too light and too dark.
Espresso is often made with dark-roasted coffee that has a strong body and little acidity. Although the roasting of filter coffee varies from country to country, it is often lighter than that of espresso. Compared to earlier times, roast styles are more flexible today. For instance, our Ethiopia Amaro Gayo espresso placed third in the espresso category at the Helsinki Coffee Festival. The espresso had a quick profile and was lightly roasted, which gave it a low roastiness and high aromatic level. Body was less bulky and more juicier. On the other hand, for some of our espressos, we prefer a fuller-bodied coffee. Then, to enhance flavour and lessen acidity, we roast the food for a little longer and extend the development stage.
Overall, honing your roasting skills is a never-ending process. There’s always more to discover about the bean. Finding the ideal roast profile for the properties of the coffee is the most fascinating aspect of my profession. I hope you enjoyed it and learned something to aid you on your coffee adventure!