How Are Coffee Beans Roasted?
Roasting coffee beans is both an art and a science. The difference between well roasted beans and a ruined batch can be a matter of seconds or just a few degrees in temperature. Therefore, creating the perfect beans for the perfect cup of coffee requires a high level of expertise and experience.
Contrary to popular belief, coffee beans are not actually beans. They are in fact the seed of the Coffea plant, and have more in common with a fruit pip than a bean. They are referred to as beans because they more resemble a bean than a seed.
Roasting involves “reading” the beans and making decisions based on the smell and sound of the roasting beans to determine the precise moment when they are ready.
Let’s find out a little more about what’s involved in roasting the perfect coffee bean.
Why Are Coffee Beans Roasted?
The raw coffee bean is green in colour and appears fresh. However, while fresh, coffee beans are not usable for coffee. In fact, they don’t even smell like coffee. Roasting the beans helps to release the oils that give coffee its flavour. Roasting also removes any bitterness from the beans and helps to develop upwards of 1,000 different flavour compounds. The quality of the roast will help to determine the flavour profile of the final cup of coffee.
The roasting process will also dry out the beans, allowing them to be ground more evenly, resulting in a better cup of coffee.
While there are a number of ways to roast coffee beans, most experts agree that the best results come from using an air roaster. Air roasters work by circulating hot air around the beans, resulting in a more even roast.
Selecting The Right Coffee Beans
Selecting the right beans is a vital part of the roasting process. Different types of coffee beans have different flavour profiles and caffeine content and require different roasting techniques.
There are two main types of coffee bean: Arabica and Robusta. Arabica beans are grown at high altitudes and have a sweeter, more complex flavour. They make up about 75% of the world’s coffee production.
Robusta beans, on the other hand, are grown at lower altitudes and have a stronger, more bitter flavour. They make up the remaining 25% of the world’s coffee production.
While Arabica beans are generally considered to be of higher quality, Robusta beans are often used in instant coffee and espresso because of their higher caffeine content.
Between both types of coffee bean are a wide variety of flavour profiles that depend on where the coffee is grown and what strain of Coffea plant the beans come from.
The 3 Stages of Coffee Roasting
There are three main stages to coffee roasting: drying, browning and development. Each step is important for releasing the flavours and aromas from the beans and preparing them for grinding.
- Drying
There are two main methods of drying coffee beans: natural (or sun) drying and mechanical drying. Natural drying is the oldest and most traditional method. Coffee beans are spread out in a thin layer on large tables or patios, where they are exposed to the sun and turned regularly to ensure even drying. This method can take up to four weeks, and the coffee must be carefully monitored to prevent over-drying or fermentation. This method is typically used in countries with a lot of sunshine and little humidity, as too much moisture can lead to mould growth.
Mechanical drying, on the other hand, uses forced hot air to remove moisture from the beans. This method is faster and more reliable, but it can also damage the flavour of the beans if not carefully monitored. As a result, most high-quality coffees are sun-dried.
The type of drying carried out will depend on the available resources and the amount of coffee being processed. Small farms often use sun drying, while larger operations tend to use mechanical dryers.
Whichever way the beans are dried, it’s essential that the drying is consistent across the beans. Unevenly dried coffee beans will roast unevenly, giving you an inconsistent cup of coffee.
- Browning
Browning, also known as caramelisation, is when the coffee aromas start to develop. During this phase the Maillard reaction occurs. This is a non-enzymatic reaction that takes place between the amino acids and sugars in the beans. This reaction creates new compounds that develop the flavours and aromas in the coffee.
At the end of the browning stage the beans will start to pop as they undergo what is known as the “first crack.” This is when the beans start to change colour and crack open due to the pressure from the heat.
- Roasting
The actual roasting phase is also known as the first crack and development phase. When the coffee beans crack a number of chemical reactions start to take place very quickly. It is at this point that the beans also release the internal heat that they built up during the first two steps of the process.
The time the beans spend in the development stage will largely determine the final sweetness and acidity of the coffee. A shorter development phase will result in coffee that is sweeter and more acidic. A longer development phase will create a darker roast that expresses more caramelised or roasted notes with lower acidity.
Cooling The Beans
After reaching the desired level of roast, the beans need to be cooled as quickly as possible to stop the roasting process. The beans are released into a cooling sieve and left to cool. If not done quickly, the beans will continue to roast and the coffee could be ruined.
While all coffee roasting follows the same basic steps (although there will be additional steps involved when preparing decaf coffee beans), it is a process that relies on the expertise, experience and preferences of the roaster. Different coffee roasteries will have different ways of roasting and it’s these variations in technique that allow for the wide range in flavour profiles in your favourite cup of coffee.
