How to Roast Coffee – Complete Roasting Guide

Since coffee became a very popular drink, humans have been interested in improving the way coffee is roasted. This process is vital to produce the second most-consumed drink in the world.

Roasting coffee is an art! This process can make your coffee the best or the worst. And if you’re a coffee lover, you should definitely know more about the coffee roasting process so you can discover which one is your favorite.

Here you will find a basic and complete guide on everything you need to know about roasting coffee. You will learn how coffee is roasted along with some suggestions, the transformation that green coffee has during this process, and the levels of roasting that configure the flavor and aroma of your coffee cup.

Grab your coffee and keep reading!

Why is the coffee roasted?

At first, coffee roasters were much more artisanal. People used pans, curved griddles, or bowls, and coffee was not roasted industrially or in bulk.

However, over the years and with the boom of this drink, spherical or cylindrical roasters were developed to make this process faster and more functional.

When coffee is collected from the plant, it is known as green coffee and is not suitable for consumption. Therefore, it is necessary that the coffee goes through a roasting process so that it can develop all its flavor and aroma characteristics. The coffee processing from seed to cup is more complex and interesting than you think.

Batch of green coffee beans
That’s how coffee looks when it hasn’t been roasted.

So what happens to coffee when it’s roasted?

Roasting is a physical-chemical process that alters the properties of green coffee. This step helps the coffee have a balance in flavor, acidity, aroma, aftertaste, and body. These properties will be different depending on the choice of the master roaster and the tastes of the customers.

During the roasting process, the coffee changes both externally and internally. The coffee bean gets to lose between 12 to 20% of weight, gain up to 30% in size, and can lose about 10% of caffeine. On top of that, during the time in the toaster, it can lose acidity, gain sweetness and also increase the percentage of fat.

Today, most coffee is roasted industrially. This allows the process to be fully controllable by the master roaster so they can obtain the desired characteristics and, therefore, have a higher quality. However, there are several coffee areas and small coffee growers that still roast coffee in a traditional way to offer a more artisanal and selected coffee in smaller quantities.

How to roast coffee?

Now let’s see how this important process works.

Coffee beans in an industrial roaster
This is what coffee looks like in an industrial roaster.

During this stage of coffee, there is a key person: the master roaster. He ensures that the green coffee is ready for consumption. This person has all the necessary knowledge to define the intensity of hot air, the time, and the desired result.

Normally, the master roaster is from the coffee farm or the coffee shop because he is fully dedicated to making this process better and better.

Now, let’s talk about the hot air that’s actually going to roast our coffee beans. In older or more artisanal roasters, coffee beans are exposed directly to heat. This makes the process more delicate and probably not so uniform. However, in modern roasters, the beans only have contact with hot air.

The burner, which can run on wood, fuel, gas or electricity, generates hot air. This air circulates through the drum of the roaster where the coffee beans are. So, this airflow that is at the temperature determined by the master roaster is what heats and roasts the coffee. Thanks to this innovation, coffee beans are roasted more homogeneously, with only one level of roasting per batch. Also, there are some alternative methods that you can check!

Depending on the air temperature, the roasting time will change. Likewise, this time will influence the flavor profile that the coffee will have, but we will explain this later.

Coffee roasting step by step

Now, let’s see step by step how this whole process is once the coffee enters the roaster:

1. Dehydration or drying:

When the bean is green it has 12% moisture. Therefore, once the beans enter the roaster, the first thing they lose is the amount of water as it reaches boiling point and turns into steam. Its color begins to change from a light green to yellow. Its size starts expanding.

At first, you may sense an aroma very similar to freshly baked bread and, a little later, when the coffee is about to have the first crack, you will smell an aroma more similar to toast, popcorn, or grass. At this point, an endothermic reaction occurs. That is, coffee absorbs energy in the form of heat.

2. Caramelization:

An exothermic reaction occurs where the bean begins to release heat. Its size is now visibly larger than its initial size. The coffee will reach a light brown color when it reaches around 170 °C (338 °F) and will have already lost about 5% of its initial weight.

In this step, the sugars begin to melt. There are three main sugar compounds in coffee that melt at different temperatures.

Fructose128 °C – 262 °F
Glucose150 °C – 302 °F
Sucrose186 °C – 366 °F

3. Thermal transition:

Maybe you’ve heard that one of the ways to know that coffee is ready is when you hear the second crack. Well, yes! It’s like when you’re making popcorn. The actual name is crackling and the coffee bean has two crackles throughout its roasting process.

These cracks occur because the coffee bean is increasing in size and its outer layer breaks to generate the peculiar S-shape in the center of the bean. At this time the first crack happens and the cooking of the beans begins. This first crackling begins when the coffee reaches a temperature of about 200 °C (392 °F) and ends around 220 °C (428 °F).

Coffees with a light to medium roast only manage to reach the first crack. Darker roast coffees will reach the second crack that starts at about 225 °C (437 °F).

4. Bean development:

The beans start roasting to continue growing and they take a medium and bright brown color. At this point, the bean has already lost about 13% of its initial weight and releases many CO2 gases.

Here, the second crack happens and the master roaster decides until what time he wants the beans to be roasted. This will depend on the taste and acidity desired. But we will explain a little more in depth the characteristics that coffee has in each level of roasting.

5. Finishing and cooling:

Once the roasting process is ready, the beans should cool down in less than 3 minutes. The reason is that inside the bean an exothermic process occurs, meaning that there is a reaction that releases energy in the form of heat. That is to say, even when the coffee is no longer in the roaster, the heat inside it continues to roast the bean. 

That is why it is so important that they are at room temperature within 3 minutes of coming out of the roaster. As it cools, the bean seals its pores in order to retain its aroma and flavor.

Transformations of coffee in the roasting process

As explained above, during roasting, the bean experiments many changes both internally and externally. Let’s learn its main transformations:

  • Its weight was reduced by 15 to 20% compared to the initial weight due to the loss of moisture and some other components.
  • The color of the coffee goes from greenish to dark brown depending on the degree of roasting. Later you will see what the levels of roasting are according to the color.
  • The coffee adopts all the aromas and flavors that are specific to that variety and that were accentuated with roasting.
  • Coffee fats increase due to the high temperatures it was exposed to.
  • Depending on the degree and time of roasting, the acidity will decrease little by little. You will also see later what acidity can be achieved at each level of roasting.

Roasting degrees

Now let’s look a little more in detail at the roasting levels. There can be two coffee batches with the same color, but with different roasting degrees and, therefore, with different characteristics in flavor, aroma, and acidity.

Coffee can be bitter and without much flavor, because the sugars were not caramelized, but instead burned. And another coffee with the same color can be sweeter and with much more flavor because its cooking was slower.

Actually, no degree is better than the other. Every country, every region, and every customer has a different taste. So here’s a guide to the roasting degrees and what features you find in each.

SCA Agtron Roast Color Kit
SCA Agtron Roast Color Kit

The numbers are a universal system for sorting and measuring the degree and color of roasted coffee. This system is called the Agtron Scale and was developed by the Specialty Coffee Association of America (SCA). It consists of “8 color disks numbered in 10% increments ranging from “Very Light” (tile #95) to “Very Dark” (tile #25)” (SCA Agtron Roast Color Kit). By using this scale, there is a standard that allows consistency among roasters and their customers too.

There are 3 great classifications: light, medium, and dark. However, within these 3 classifications, there are other subcategories according to that scale.

Extreme Light> 95
Very Light85 – 94 
Light75 – 84 
Medium – Light65 – 74
Medium55 – 64
Medium – Dark45 – 54
Dark35 – 44
Very Dark25 – 34
Extreme – Dark< 25

As we have mentioned, depending on the level or degree of roasting, the coffee will have special characteristics in body, flavor, and aroma. Let’s see how it works:

LightThe coffee is bigger and reaches only the first crack. Low body with a lot of acidity and a mild flavor. Not very recommended for espresso. It is ideal for a drip coffee maker. The bean surface is dry because it has not released fats.Herbal and fruity notes. Flavors of origin predominate.
MediumAfter a few minutes after the first crack, the coffee is medium brown. It is very popular in specialty coffees in the United States.Medium body with less acidity and more bitter flavors. It’s a little sweeter than light roast coffees. The surface of the bean is still dry. It works for both espressos and softer coffees.Nuts, caramel, and chocolate.
DarkThe second crack happens. At this stage, the coffee releases its oils.It has a stronger body and has lost acidity. It can be a little spicy but it balances very well with the sweetness. The aroma and taste are more intense. Ideal for espresso. The bean surface is a little shiny.Flavors of spices, dark chocolate, and slightly smoky nuts without being unpleasant.
Extremely darkAfter the second crack, the coffee starts to smoke a lot. Sugars are no longer caramelized but burned.It has a sweet but smoky taste. Its notes are lost and it tastes burnt. It doesn’t have much flavor or aroma.Totally smoked.

Coffee roasting suggestions

Coffee quality

Having good raw material is the first step. If green coffee was not grown the right way or is not of the best quality, roasting will not have the best results either. Remember that green coffee already comes with pre-defined flavors and characteristics and roasting is responsible for highlighting those characteristics. But it all depends on green coffee.


The roaster, without a doubt, is your main ally right now. So be sure to choose one where you can adjust the temperature and that also has a cooling system. It will also be very useful that the roaster has a sampling system, since this allows you to have more control of the process and compare that batch with the degree of roasting of another sample or the Agtron disks. If you plan to buy a roaster and you can’t decide on a specific one, stop by our selection of the best coffee roasters in the market.


Use a stopwatch to keep track of time and, along with the temperature, achieve the ideal roasting.

A good roasting time ranges from 12 to 20 minutes. However, this will depend on the roaster, temperature, and wanted degree of roasting.


Even if it sounds irrelevant, the place where the roaster is should be properly lit so that you have a clear view of the process. It is best that the space has white light so that you can distinguish the different roasting colors.

Roasting curves

The master roaster must keep track of the roasting curves. This is a graph that shows the behavior of roasting depending on temperature and time. Then, the roaster should keep track of these curves to reach the ideal one according to the desired degree of roasting.


Roasting coffee is one of the most important steps during its transformation process. Knowing and doing this process the right way ensures having a coffee cup with a good aroma, flavor, and body. To say that one level of roasting is better than the other would be a generalization.  Each level of roasting is perfect for a type of brewing and for a specific taste.

Getting to know the art of roasting coffee is a path full of experiences and efforts. The coffee tasters are in charge of developing your palate to find all the flavor notes that arise from the roasting of the coffee. So you can also taste several levels of roasting to continue enjoying this drink. What level of roasting is your favorite?