Coffee Roasting Process: Essential Guide

Updated Nov 26, 2023 • Donna Lu

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Coffee Roasting Best Practices (Part 4 of 5)

Do you want to sample the best-tasting artisanal coffees from the comfort of your home? Or are you planning on opening a roastery or coffee shop? Equipping yourself with the right coffee-roasting skills is the best way to succeed. 

Whether focused on churning out the best single origin or blended coffee, a delicious house blend, or your favorite personal home blend, having the right roasting skills will help you do so. After all, with proper harvest, transport, and storage, roasting is the next most important part of achieving a fantastic coffee aroma, taste, and body. 

The best part of this process is that you can control the entire process. So, we've put together a foolproof and exhaustive guide to the ideal roasting process to ensure you do it right.

Roasted Beans in small glasses: dark, medium and light.

Overview of the Coffee Roasting Process

Coffee roasting simply refers to turning green coffee beans into brown beans with more flavor and aroma. Roasting turns unroasted coffee (usually from green to grayish green and yellowish green with a subtle, non-coffee-smelling, grass scent) into brownish beans with fragrance and flavor.  

The process involves using heat to alter coffee beans' chemical and physical properties. This, in turn, activates and unlocks the flavors and aroma once locked in the green beans. The heat helps to remove the chlorogenic acid of the green beans.

The temperature of the roasting process plays a significant role in how much chlorogenic acid is removed. This, in turn, affects the roasted bean's flavors, aroma, and caffeine levels. Contrary to what many people may believe, a higher roasting level results in lower caffeine levels. 

This means a light roast coffee blend contains more caffeine than a dark roast blend. While a light roast blend contains more caffeine, dark roast blends tend to be slightly bitter with more flavor depth due to their longer roasting duration.

Coffee beans being roasted

How Does The Coffee Roasting Process Work?

The actual coffee roasting process works in three distinctive stages. These include the drying, browning, and roasting or development stages. Each stage comes with its purpose and importance. In general, coffee beans are dried before proceeding with actual roasting.

3 Important Stages of Coffee Roasting

Here’s how each stage works;

The Drying Stage

After harvest, green coffee beans are usually dried in various methods to allow for safe transport and storage before the final destination. Nonetheless, they still contain some moisture level, about 8 to 12%. So, to truly ensure influential roasting, you have to first start by completely drying the beans. Internal temperatures during the drying stage can reach up to 165 degrees Celsius.

This first stage involves adding the beans to the roaster to dry them, turning their appearance from green to yellow. The duration of this process depends on the type of roaster used and the size of the coffee batch. Generally, a drum roaster will use about 3 to 8 minutes with a standard-sized batch.

The Browning Stage

If you are familiar with coffee roasting, “Maillard reaction” should be new. Maillard reaction simply refers to a lineup of chemical reactions responsible for developing the color and flavors of the coffee being roasted. The flavors are developed in this stage, and the yellow bean turns brown. 

During the roasting process, the release of heat forces the increase of internal pressure that causes the cell walls of the coffee beans to break. This, in turn, forces the beans to pop or crack. After the first crack, the process transitions to the third development or roasting stage.  

The Development Or Roasting Stage

The very beginning of the development stage interlays with the end of the browning stage as the beans pop or crack. This first crack of the bean usually produces a light roast level or roasting. The development stage focuses more on achieving the flavor depth and aroma that the roaster wants. 

However, to ace this stage, you want to slow it to eliminate the risk of ruining your coffee. Maintaining the same roasting speed and heat can cause the coffee to over-roast and develop a sharp and smoky taste. Generally, the development stage uses about 15 to 25% of the total roasting duration, depending on the level of roast you want to achieve. 

A longer roasting duration provides more flavor and aroma depth, while a shorter duration means the roast has a higher caffeine level. On the other hand, experts will opt for quick roasting as it produces the desired aroma faster. But slow roasting gives you better control over the flavor development, ensuring you get the taste and aromas you want. It also prevents overroasting!

If you want to be sure about your Roasting Levels, you can always use a color meter to pinpoint the levels.

In this ''3 stages of Coffee Roasting'' video by Coffee with Kian, you can observe the 3 important stages of coffee roasting:


Roasting Factors to Consider

You can use a cross-section of factors to ensure you are on the right roasting track. These factors can also be used as roasting level indicators. 

Roast Degree

Measured by a color meter or by simply tasting, the roast degree is a simple roast indicator. While experimenting with different flavors and blends, the roast degree helps to pinpoint the level you achieved. For instance, acidic or fruity flavors are usually light roasts. 

You usually get fruity notes from light roasts due to the higher organic compound levels attributed to the shorter roasting duration. On the other hand, slightly bitter and burnt-like flavors are usually dark roasts. 

When the coffee reaches the dark roast level, the organic compounds are usually broken down while sulfuric compounds increase to give off the burnt-like and roasted flavors. Since light roasts contain a good amount of organic compounds, it is easier to differentiate between different types of green coffees using light roasts than dark ones.

Roast Time

Some roasters usually champion fast roasting, while others champion slow roasting. The good news is that both roasting styles are suitable; you must decide correctly when to use either. For instance, fast roasting lets you get the ideal aromatic compounds and enjoy all flavors of the particular bean. However, fast roasting doesn’t give you much control over flavor development. Additionally, you can burn your beans during fast roasting if you don't exercise extra attention. 

On the other hand, slow roasting does the opposite. It allows you to control the flavors and achieve the profile you want from the beans. For instance, a good espresso blend is without acidity or minimal acidity. With slow roasting, you can ensure organic acids break down effectively, resulting in a less acidic blend.

Coffee bean roaster with a timer

Levels of Roasting

Here are the five typical roast levels;

Light Roast coffee 

Light Roast coffee refers to coffee roasted in the shortest duration and is usually done right after the first crack. The internal temperature of light roasted coffee ranges between 180 and 205 degrees Celsius. Light roast coffee is sometimes called New England, Half-City, or Cinnamon. 

These blends usually have internal temperatures of 190 degrees Celsius (Half city), 196 degrees Celsius (Cinnamon), and 205 degrees Celsius (New England).  Lightly roasted beans tend to have oils due to the shorter roasting duration. 

They also have fruity flavors, lemony and citrus undertones, more caffeine, and acidity. Since light roasts don't complete their chemical reactions, they come in varying flavor profiles based on their organic compound content and origin.

Medium Roast Coffee

Medium roasts typically reach an internal temperature of 210 to 220 degrees Celsius and are made after the first crack just before the second one occurs. Medium roasts include American roasts (210°C), and City Roast (219°C). Medium roasts have slightly more depth of body with little acidity than light roasts. Many house and breakfast blends are usually medium roasts.

Medium Dark Roast Coffee

Medium dark roast coffee achieves a rich and dark color with some oil on the surface and has an internal temperature of 225 to 230 degrees Fahrenheit. They have more body than medium roasts and a slightly bittersweet taste. Further, they have a fuller bodies and less acidity. 

Medium dark roast coffee is achieved during or just after the second crack. Famous medium dark roast examples include Full City Roast (225 °C) and Vienna Roast (230 °C). Other examples include continental, light French, and light espresso roasts.

Dark Roast Coffee

Dark roast coffee uses the most extended roasting duration and usually has visible oils on the surface due to the high temperatures. The internal temperature for dark roast coffee ranges between 240 and 250 degrees Celsius. Common dark roasts include French roast (240 °C), Italian roast (245 °C), and Spanish roast (250 °C). Others include Turkish, dark French, and heavy. 

Every organic compound must be broken down to achieve dark roast levels, making it impossible to taste any original flavors. So, you must masterfully create this level to ensure you don’t get any overly smoky or burnt flavors. Unlike lighter roasts, dark roasts are sweeter as the longer roasting time allows the sugars in the bean to caramelize. 

However, they also develop some bitterness, unlike light roasts' fruitier and lighter citrusy flavors. Additionally, dark roasts develop rich and full-body flavors with a buttery finish and very minimal caffeine levels. Medium roasts are synonymous with American roasts due to the American love for medium roasts. On the other hand, you will notice that different dark roasts are named after Europeans who prefer darker roasts.

Different colored coffee beans from green to light, to medium and dark roasted

Importance Of Monitoring The Roast 

As mentioned above, the roasting process is usually delicate and precise. The slightest mishap can ruin your coffee batch by under or over-roasting. You want to exercise particular care when fast roasting. 

Losing track of the process can easily lead to burning your beans and ending up with burnt and smoky-tasting coffee. Additionally, the activity of the roasting determines the roast level. For instance, light roast coffee is usually achieved after the first crack. 

So, leaving the coffee to continue roasting if you miss the first crack may lead to other roast levels, like a medium (achieved during or right after the second crack). In addition to monitoring your roasts, you can use tools like color meters to confirm the roast level and maintain consistency for all your batches.

A person checking the state of his coffee beans being roasted

Best Practices For Controlling The Roasting Process 

For the best results and consistency, controlling the roasting process is important. The good news is that there is a cross-section of the best practices to help you do so.

Plan Ahead

Put together a guide or SOP for your roastery. This ensures you have your space correctly organized and your entire equipment ready before the roasting process.

Schedule is Vital

Schedule your roasting routines to be identical. This is a fundamental concept for commercial roasteries or coffee shops. After all, you want consistency across all the batches you roast. You have to maintain the controls on all the tools used. 

These include the level of preheating for the roaster (how much heat will be stored) and even how long it takes to empty your coffee batch into the cooling tray before roasting the next one. Even the minor details, like how long you wait before transferring freshly roasted coffee to a cooling tray, matter and affect taste and aroma! 

Understand the Technicalities

The roasting process involves heat transfer, primarily conduction, and convection heat. Make it a point to familiarize yourself with these concepts and how they affect the entire roasting process. Conductive heat transfer happens when the roaster comes in contact with the beans, transferring the heat to the beans. 

On the other hand, convection heat transfers heat through airflow to the beans as they are tossed in the roaster (e.g. a drum roaster). In addition to knowing how these work, it’s also crucial to remember that influential roasting requires both types of heat transfer. This, in turn, guarantees even and effective roasting across the entire batch. 

Preheat the Roaster Machine

Like an oven, your roaster should be preheated. The same disappointing results you get from baked goods when you don't preheat the oven are the same you will experience with your coffee in a non-preheated roaster. Skipping the preheating process means your roaster needs more heat stored to transfer and heat the coffee effectively. In turn, you may end up with unevenly roasted coffee.

Roasting Speed

Always pick the proper roasting technique and stick to it. Whether it’s fast or slow roasting, you want to equip yourself with the proper knowledge to handle your chosen method. Slow roasting gives you more time to develop your flavors and is less critical. On the other hand, fast roasting is better favored for expert roasters. 

Data Collection is Key

Data is king! Consistently track and compare your roast information for every single batch you roast. This will ultimately help you decide the best blends to continue with and what parameters to change. In the beginning, you will see yourself making multiple changes. This shouldn’t be a problem. These changes will help you pinpoint the right SOPs, plans, schedules, and the best roasts and blends.

Tips For Achieving The Desired Roast Level

One way to achieve the desired roast level is to stick to the practices that help you control the roasting process. You can also use tools like color meters to help you quickly identify the roast level. Ultimately, trial and error is the only best way to ensure you reach the desired roast levels. 

This explains why data collection is vital. Along with data collection, you should stick to any roaster and barista’s favorite practices, i.e. cupping. Cupping refers to the professional practice of coffee tasting and observing factors, such as the aroma, flavors, acidity, and aftertaste. 

The roaster or barista typically samples brewed coffee from roasted blends to pinpoint the descriptors and decide which blends are ideal. In addition to helping you reach the roast levels and achieve the desired flavors, cupping is also an excellent quality control technique. After all, roasters are advised to sample every roast to ensure they meet the standards.

Meet the expert

Donna is a coffee lover and freelance writer from Tanzania. Coffee runs deep in her family, tracing its roots to her grandmother’s running of their first coffee farm in the mid-70s. During the summer seasons, she enjoys writing and co-running her grandmother's small robusta coffee farm with her sister in northwest Tanzania.

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