Roasting is a crucial step for good coffee as this process helps develop the bean’s flavours and aromas.
The roasting profile will depend on the brewing method and the flavour profile you want to achieve for your coffee.
However, a bit of coffee knowledge is needed in order to successfully roast your own coffee beans with a home coffee roaster.
Below, we outline the basics of coffee roasting, explain the different stages and types of roast, and answer some commonly asked questions so that you can start roasting in no time.
What is coffee roasting?
Coffee roasting involves the process of transforming green coffee beans to brown. It involves three stages: drying, browning and development, which we will discuss later on.
Roasting helps develop the aroma compounds that are not yet present in green coffee while increasing the coffee’s solubility. When roasting, the beans go through several chemical reactions that will lead them to the perfect roast profile.
Different roast levels will bring out different flavour profiles.
Each roast level is designed with a specific brew method in mind. Most light and medium roasts are destined for pour-over while medium, medium-dark and dark roasted coffee tends to be used for espresso.
Roasting is usually done with a commercial roaster. This type of roaster has a metal cylinder that mixes green coffee beans while roasting them.
However, home coffee roasting has become popular throughout recent years thanks to easy access to high-quality green coffee beans and small home roasters.
Types of roast (Roast degree)
Light roast coffee is usually intended for pour-over coffee. This type of roast features a light brown colour and no oil on the surface.
Light roasts are achieved by stopping the roasting process at “the first crack” (more on this later) and are perfect for showcasing delicate notes such as lemongrass, jasmine, tea and tropical fruits.
A light roast can also be called a cinnamon roast or a light city.
Medium roasts are one of the most popular. They have a brown colour and no oil on the bean’s surface.
These roasts are perfect for showcasing fruits, caramel, nuts, and chocolate notes.
A medium roast is usually preferred for espresso and it is achieved by stopping the process after the first crack.
Medium-dark roasts start to develop less acidity and are usually pulled out before reaching the second crack. This roast is also known as an American roast or city roast.
Darker roasts have a dark brown colour and the bean surface becomes very shiny thanks to the natural oils.
A dark roast coffee bean has very low acidity and showcases notes of dark chocolate, caramel and brown sugar.
Dark roasts are also known as full city roast, Vienna roast, French roast or Italian roast. These beans also have a characteristic dark colour.
The stages of coffee roasting
The drying stage sets the foundation for the following two stages of roasting. It is in this stage that you will control how fast the roasting process will be.
Drying the coffee happens before the actual roasting and it tends to last between 4 to 8 minutes at 160 C.
In this stage, most of the water inside the beans starts evaporating and the bean starts collecting heat.
In this stage, the coffee beans start giving off the traditional coffee aroma.
During this step, the all-important Maillard reaction happens.
The Maillard reaction is when the sugars inside the beans are reduced and transformed. It is what gives coffee beans their distinctive flavour and colour.
This stage is when the cracking sound happens. This process happens because the bean has been collecting energy and heat throughout the two previous stages.
When the moisture and heat become too much, the coffee cracks, making a sound similar to a popcorn machine.
Most light roasts are stopped after the first crack while dark roasted coffee will continue to develop until a second crack is heard.
The sound is an indication for you to either continue or stop your coffee roasting process.
How to determine the appropriate roast time
Roast time depends on several factors such as batch size, coffee bean variety and the type of roast you want to achieve.
However, the roasting process tends to last between 5 and 15 minutes.
For light roast, stop the roasting right after you hear the first crack, usually during the first 5 minutes.
Medium and dark roasts need more time to develop which means that you are looking to stop the roasting a couple of minutes after the first crack or once the coffee has the desired colour.
We suggest checking the beans constantly to ensure that they do not burn.
The time you choose to end your roasting process will depend on the roast profiles you wish to develop.
Darker roasts tend to be sweeter while lighter roasts have higher acidity.
Most blends and espresso beans are stopped before the second crack.
Roasting that finishes in a short time, usually after the first crack, will result in coffee that works great for pour-over.
What is the first and second crack?
When roasting coffee, the beans go through a series of chemical relations that involve heat transfer. This reaction is called the Maillard reaction, as mentioned previously.
Throughout this stage, the beans have been building internal pressure and lowering their moisture content.
Once the beans reach a temperature of approximately 196 celsius, they will make a sound that is similar to popcorn popping. That is called the first crack.
Most roasters finish the process after the first crack, once the aromas have developed.
The second crack happens after the bean has retained enough heated air to expand and break out of the outer shell once again.
During this stage, the beans are roasted until they develop more sweetness and a darker colour. The darker the bean is roasted, the less acidity it will have.
How to roast coffee at home
Before you try your hand at home roasting there are some things that you need to know. A good quality green bean is essential. Some specialty coffee roasters sell unroasted beans that you can buy by weight.
Another key element is a coffee roaster. Finding the correct roast machine for your needs will make the process easier by knowing what you are looking for and what interest you the most. We suggest taking a look at our guide to the best home coffee roasters.
Home roasting is a slightly different process than commercial roasting.
Most home roasting machines work similar to a popcorn popper, pushing hot air into the beans until they start roasting. Others are designed to be placed on top of stoves.
Once you have your home roaster you are ready to start.
- Pour unroasted coffee beans inside the roaster and close it. The amount of beans may be restricted by how big your roaster is.
- Turn on the coffee roaster and allow the beans to start gathering up heat inside. Each roaster is different so you will have to monitor the beans carefully and keep an eye on the colour.
- High temperatures are required for the first crack. You will know when this point arrives because the roasted bean will start releasing a pleasant aroma and making a popping sound.
- If you are using a stovetop popper instead of one of the drum roasters, make sure to keep moving the green beans in order for them to roast evenly.
- Most commercial roasts are stopped after the first rack. Once you see the desired colour turn off the roaster and transfer the beans to a different container to cool. You can cool them by moving the beans back and forth between two colanders or stirring them with a spoon.
- Once the beans have completely cooled, you should leave them in the open for 12 hours so that they can start releasing CO2. After 12 hours, you can store them in an airtight container. Roasted coffee can last for up to six months if stored correctly.