Coffee. The journey starts with green coffee beans and ends with the perfect drink made to your liking. Whether you prefer cold brew, drip or filter, espresso or any other possibility, what they all have in common is that they all start with chickpeas. In this article, we share the basics behind the roasting process of coffee beans. What steps must green coffee beans go through to finally become the delicious roasted coffee we all know and love, and what is the science behind it?
1. Drying green coffee beans
Since green coffee beans have about 10% moisture, we need to dry the coffee beans before starting the roasting process. Since all O Tesla roasters are 2-layer drum roasters, coffee beans need about 6-8 minutes to complete the drying process. Temperature control of the roaster is extremely important at this point as you don't want the coffee to burn during the drying process. When this stage moves to the next, the temperature of the coffee will be around 160oC.
2. Browning the coffee
The browning stage is the stage where the aroma of the coffee beans will begin to develop. In other words, we convert aroma precursors into fragrance compounds. Although this stage continues with the drying phase, the coffee beans have not yet completed the drying process. During the browning process, we see the Maillard reaction taking place. This means that the natural sugars and amino acids in the coffee bean begin to react and give the coffee its distinctive color and flavor. Naturally, the roasting process begins to slow down after the reaction. Some roasters want this process to be slowed down as it can help develop more flavor of the coffee. Obviously, this all depends on your preferences as a roaster. During the browning process we see the appearance of roasters known as the “First Crack”. This means that the coffee beans are blooming which will take us to the next stage.
3. Roasting coffee beans
This is the stage where you as a roaster can fully shape the flavor you are looking for. Roasting too quickly will result in a smoky and overly sharp coffee. Trial and error roasting is the key to finding that perfect profile.The expanded coffee beans now begin to release all the heat that was built up in the previous stages, known as exothermic heat. The roasting stage reaches the desired aromatic compounds.
3.1 Degree of roast
Roast level is one of the most important factors to use when indicating your roasting process. The color of the beans tells you a lot when it comes to finding that perfect roast. Lightly roasted seeds have a sour, sour taste while dark roasted seeds have a more bitter taste. Also, lightly roasted seeds are known for their more fruity flavors while dark roasted nuts often have a slightly burnt taste. This is possible because lightly roasted seeds contain the organic compound hydroxymethyfurfural which gives the fruity flavor to lightly roasted seeds. However, this compound can break down as roasting progresses further, resulting in dark roasted beans with a burnt taste. Basically, we can assume that lightly roasted beans give a better taste of pure coffee.
3.2 Roasting time
The degree of roasting plays the biggest role when it comes to determining the exact flavor of the beans. However, roasting time also plays an important role in this process. The guiding principle here is that the connection between all stages is the most important. Roast quickly and you create more aromatic compounds but there is a risk of astringent coffee. When you roast slowly, you have more control over the flavor development of the beans.Example: When you want to create a blend with less acidity to use for espresso, slow roasting can be a good idea. This is because acids have more time to break down as you give them more time during roasting.
4. Cooling roasted coffee beans
After roasting, we let the roasted coffee cool. An important step in the basics of coffee roasting as the beans need to be cooled as soon as possible for the roasting to stop. The cooling process is something you don't have much control over. You discharge the roasted coffee beans, they enter the cooling sieve and the cooling process begins. Like mentioned earlier, the coffee must be cooled down within 4 to 5 minutes to ensure that the roasting process does not continue. When the coffee cools, that marks the end of the roasting process.
5. After roasting the coffee, how do you check the results?
To evaluate roasted coffee, most roasters use a process called a challenge. Treasure is one of the more famous ways to prove your results. This process is based on the skill and experience of the coffee awakener. This process involves inhaling and tasting, all to get a clear picture of the flavor you have created.The exact way everyone does challenge sessions is different for each roaster. As you can imagine, everyone has their own workflow and professional secrets to creating their own independent fusion. It is entirely up to you as a guide how you fill out your versions and what aspects and outcomes are most valuable to you.
Our goal is to explain the basics that you will experience when roasting coffee beans. Please understand that each roaster has its own preferences, working methods and ingredients, which means that many of the steps described may vary depending on the roaster you visit. This makes the journey to the perfect roast fun, not an overnight process and for a roaster it can be as exciting as the final product!