The growing and processing of coffee determines the quality of raw coffee beans. Roasting on the other hand helps bring out the true flavours from these beans.
While some prefer buying the green beans that can be roasted at home, few others prefer the roasted beans that can be ground fresh and consumed. The majority are the ones who choose the ready-to-use coffee sealed in pouches and brew their drink.
Roasting is both an art and a science which, when greatly mastered, produces an incredible cup of coffee.
Grandpa is keen on experiencing how coffee is roasted and what it takes to produce that perfect cup. Let’s see what he discovered when he went to a coffee roasting session in Bangalore. Along with him are other interested learners who are exploring the training session.
A few questions that run on everyone’s mind trying to discover coffee are - Why roast coffee? Can’t green coffee be consumed as it is? How different are they both?
Roasting coffee helps bring out more flavours and aromas which can be controlled and modified based on one’s preferences. Green coffee, on the other side, tastes grassy and pea-like. Although it’s more popular these days to consume green coffee for its benefits, a traditional coffee drinker would like a regular coffee any day.
So, it’s quite clear that roasting coffee brings a totally different character in the cup. Now comes another question – why is roasting so important? What happens after coffee is roasted?
To answer such queries and help understand the science and art of coffee roasting better, the trainer Mr. Ram starts explaining.
“Roasting of coffee turns the pale green beans to brown roasted beans. This process involves a lot of chemical reactions as well as physical changes to the bean. Now, it makes sense as to why science is involved. Let’s look at these changes and understand the reactions.
“Firstly, coffee that is pale green in colour is fed into the roasting machine, at a starting temperature of 160°C. In the roasting machines, heat is mostly transported through conduction and convection i.e., direct contact and forced convection by supplying heat through hot air that is blown into the machine.
“Secondly, the drying phase starts when changes in the colour of the beans can be observed. The beans turn to white or light green in colour. This phase typically lasts for about 3-5 mins. The beans start to absorb the energy from the heat supplied and water starts to evaporate. There is a green, pea-like aroma. At the end of this phase, the beans are light yellow in colour.”
Just when everyone is eager to observe the changes, Mr. Ram takes out a small sample from the roaster and describes it better.
“Thirdly, the browning stage starts when the colour of the beans changes from light yellow to light brown. Pressure builds up in the beans due to several reactions inside and there is a toasted aroma that is similar to that of baking. Roasting slows down at this stage and flavour starts to develop. This phase lasts for a short period and changes are observed in the 4th or 5th minute.
All the participants from the training batch bring their ears close to the roaster to hear the feeble sound of coffee beans popping and cracking. “Although it’s difficult to notice these changes immediately,” says Ram, “with time one can acquire this skill. It is also during this stage that the aroma of roasted coffee can be noted.
“Fourthly, the first crack starts at the 7th or 8th minute. A typical cracking noise along with a popping sound and mild smoke is noticed. There is maximum pressure inside the beans and they start to release the energy in the form of heat accumulated during the process and crack at the grooves. Gases are formed which smell like coffee. It is only through roasting that the volatile compounds release from the coffee. By the end of this stage, the bean surface is smooth, shiny and matt-like. Now the beans start to darken, the acids degrade slowly and the body develops (which is the texture or the mouth feel of a coffee). Roasters like to slow down the process by increasing the time and reducing the energy to slowly let the flavour develop in the coffee beans.”
Fifthly, the second crack begins somewhere at the 10th or 12th minute. An intense cracking noise can be heard. The beans become dark very fast and also bitter substances are formed as a result of breakdown of organic compounds. If the beans are further left in the roaster the coffee develops flavours entirely different from the original characteristics. Coffee releases smoky, burnt flavours and gives out a bitter taste. Oil starts to build up on the surface of the beans. During this phase, most of the bean mass is lost in the form of gas due to burning of organic material. There is an increased risk of fire in the bean or chamber due to pyrolysis.
While the trainees put their thoughts on experimenting with the types of coffee and creating blends using various proportions of each variety the trainer explains a lot more about the art of roasting.
It is very important to maintain a homogeneous roast which is a balance between the external and the internal heat transfer. Several factors influence how a batch of coffee that is roasted tastes.
Coffee roasting is more of an art than science because all the reactions are common to any bean type. Understanding the beans and creating roast profiles based on the bean type is a skill that only a roast master has. It takes great effort and observation to notice the slightest change in the roaster – be it physical in terms of a sample to check the colour of the beans, aroma of the coffee or the popping sound from its cracking. Many factors influence the beans before and during roasting like bean size, humidity, temperature, moisture content and age of the beans. It is for this reason it takes a great skill to roast a perfect batch everytime.
Shorter roasts produce coffee with increased acidity and body and with decreased bitterness. Fast roasting develops strong flavours and aromas. On the other hand, long roasting has decreased acidity and body but higher bitterness. Changes happen very slowly which make it difficult to achieve a desired profile and flavour.
Roast profiling is the process of creating specific profiles to maintain the consistency of certain coffees. To ensure an even tasting coffee every time, it is important to maintain a roast profile. This could be done by procuring the same quality of green beans, storing the profile in systems, maintenance of the roasters, skilled roasters to roast and create blends and finally tasting the coffee. All these factors significantly result in creating coffee that has a consistent flavour and taste.
Well, that’s not the end. Coffee that’s roasted is left in open for 12 – 24 hrs and later packed or ground further. It’s best consumed within a week while it can be stored for up to six months in airtight containers.
Coffee roasting affects most of the flavours in a cup. But did you know that the grind level and the equipment used for extraction of the decoction also affect how a cup of coffee tastes? Get familiar with the process of Coffee Grinding & Cupping.