Coffee Roasting Stages: A Guide For Roasters
Coffee roasting stages is one of the lesser-known topics that is widely debated among coffee roasters but rarely discussed among the coffee community.
Perhaps it does not concern most of the regular coffee drinkers out there. But I am sure there are a couple of curious souls out there who are itching to know a thing or two about coffee roasting stages.
After all, the process of making coffee involves coffee roasting. And that is why you are here.
Without further ado, in this blog post, I am going to deep dive into the coffee roasting stages and break them down into bite-sized information.
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At a glance: Coffee Roasting Stages
Coffee Roasting Stages
From my Coffee Basics post, we know that coffee beans are actually the seeds of the coffee cherry fruit itself. After the seeds are separated from the fruit and left to dry, what is left is the coffee beans in their rawest form.
It is also known as green coffee beans.
The green coffee beans will then go through a roasting process to turn them into familiar coffee with a brown hue as we know.
So the process of roasting coffee beans is not as simple as just exposing the green coffee beans to heat and hoping they will turn out great. Coffee roasters take pride in hand-crafting these coffee beans as the whole process is pretty delicate.
With that in mind, the coffee roasting stages can be divided into 6 phases which are:
1. Drying Phase
2. Maillard Phase
3. Caramelisation Phase
4. First Crack
5. Development Phase
6. Second Crack
Let us go through each of these coffee roasting stages and see how they affect the coffee beans.
Stage 1 – Drying Phase
Coffee processing involves drying out the coffee beans in the sun over a week. However, the green coffee beans will not be completely dry and one would expect approximately 10% moisture left in the coffee beans.
Hence, the first part of the coffee roasting process is to remove moisture.
The coffee roasting machine will first be preheated up to approximately 200oC (392oF) before green coffee beans are loaded into the drum. From here on, the coffee beans undergo an endothermic phase where heat is absorbed and the water will start to evaporate.
Physically, the drying phase will change the green coffee beans into a yellow hue and the mass of the coffee beans will gradually drop as their moisture content reduces.
Generally, roasters will not rush through the phase of drying to ensure proper heat distribution throughout the coffee bean. Progressing to the next coffee roasting stage with a short drying phase will result in underdeveloped coffee beans while the extended drying phase will cause overdevelopment of the coffee beans. Both of which will have undesired flavors.
As a guide, the drying phase usually lasts about 30% to 50% of the total roasting time (Approximately 4 to 8 minutes). I will discuss more on the development phase below.
Author’s Note: Although this phase is known as the drying phase, you should know that the drying process does not stop right after this point. In fact, the drying process takes place throughout the whole roasting process of coffee.
Stage 2 – Maillard Phase
The Maillard Phase is a reference to a French physician and chemist, Loius Cammile Maillard, the man who first discovered the Maillard reaction. Simply put, the Maillard reaction is a chemical reaction between amino acids and sugars in foods when exposed to high heat.
To illustrate the Maillard reaction, think about the caramelization of grilled meat and the browning of bread in a toaster. This process enhances the flavors and aroma of the food.
And so, the same process applies to coffee beans as they are being roasted.
So what happens to the coffee beans during the Maillard phase?
During the Maillard phase, sugars get broken down and react with amino acids to form a myriad of flavor and aromatic compounds. Since coffee beans from different regions have different compositions of sugars and amino acids, they will eventually form different flavor compounds during this phase.
Hence, this results in many interesting flavors of coffee. I’ve written a piece on the flavor notes of coffee if you are interested to know more!
And of course, you will start to get a whiff of the intoxicating pleasant aroma of coffee due to the Maillard reaction on the coffee beans. During this phase, the coffee bean’s temperature would have risen to approximately 250oC – 300oF (121oC – 149oC).
Stage 3 – Caramelisation Phase
As the coffee roasting stage progresses from the Maillard phase, the caramelization phase will kick in as the coffee bean temperature approaches the range of 340oF (171oC).
The sugars caramelization process will gradually put a halt to the Maillard phase as it degrades sugars which are supposed to facilitate the Maillard reaction. Here, roasters will usually prolong this phase to develop flavor profiles such as nutty and caramel.
In terms of color, the coffee bean will have now changed from a yellow hue to a light brown color. The coffee beans are finally looking like the coffee beans we are familiar with!
These coffee beans will also start to shed the outer layer which is known as the silver skin (also known as the chaff). This may give rise to a potential fire hazard as the silver skin may catch fire and burn up in the roasting drum. As such, coffee roasters must ensure adequate airflow through the roasting drum to vent out the silver skin and smoke.
Author’s Note: Both Maillard and Caramelisation phases sacrifice sugars to develop different flavor compounds of the coffee beans. Naturally, the natural sweetness of the coffee beans will reduce while bitterness will slowly rise. Coffee roasters will have to balance these timings in order to bring the best out of the coffee beans they are roasting.
Stage 4 – First Crack
The first 3 coffee roasting stages, it is pretty uneventful other than having to monitor the bean temperature and color change over time. All of this changes when the First Crack stage happens which is at 196oC.
During the drying phase, the steam builds up within the core of the coffee bean causing a rise in internal pressure. Aside from steam, Carbon Dioxide gas molecules from within the beans receive heat energy during roasting and are now excited to move around.
Consequently, the pressure combination from both steam and Carbon Dioxide will tear through the surface of the coffee beans. This results in a pop-corn popping sound in the roasting drum.
As this happens, the size of the coffee beans will increase slightly due to heat expansion and also due to steam and carbon dioxide causing internal cracks within the coffee bean. Color-wise, the brown color is more developed from the Caramelisation phase.
The chaff of the coffee beans will also rapidly be shed by the “violent” popping action and smoke generation will intensify in this stage. For this reason, a vent and also good internal ventilation of the roasting room is of utmost importance.
If the roaster decides to stop the roast at this point, the coffee bean roast level is known as a City Roast (Medium Roast Region)
Stage 5 – Development Phase
The Development Phase is the phase where the coffee roaster’s experience plays an important role.
However, you must know that the development phase is not a defined period within the coffee roasting stages progression. Instead, the development phase is a phase that happens concurrently with the other roasting stages.
In other words, every stage that was described before this plays a role in developing the flavors of the coffee beans.
That said, most roasters would agree that the development phase is the phase right after the First Crack. Post-first crack, roasters will try to control the temperature of the beans to be relatively stable to develop the coffee beans.
Underdeveloping the coffee beans will cause the core temperature of the coffee beans to be cooler than the exterior. Consequently, brewing coffee from this batch will exhibit sour coffee flavors which are not desirable.
On the contrary, overdeveloping the coffee beans will destroy most of the flavor compounds.
Stage 6 – Second Crack
Right after the First Crack, further roasting the coffee beans will then cause the second build-up of Carbon Dioxide gas within the coffee bean’s core. Since the First Crack ruptured the internals and surface of the coffee bean, the Second Crack is naturally not as loud and pronounced as the First Crack.
Nonetheless, an important indicator to tell the roaster that the coffee roast levels are now approaching the Dark Roast region.
As the structure of the coffee bean is weakened, this allows coffee oils within the core to seep out as the roasting process approaches the Second Crack. Physically, coffees that are roasted to the Second Crack phase will have a dark brown color and a distinct layer of oil on their surface.
In terms of flavor, you should expect all the natural flavors and characteristics of the coffee bean to be lost. Instead, they have now been replaced with bold bitter smoky flavors with minimal acidity.
Trivia
Did you know that coffee beans of a lower quality are usually roasted beyond the Second Crack phase to yield Dark Roast coffee (also known as French or Italian Roast)?
This masks any defects in the coffee beans and the coffee brewed from these beans will be full-bodied and extremely bitter. This calls for milk pairing along with sugar to make the coffee more palatable.
Roast Progression Curve
As we go through all 6 stages of coffee roasting, it can all be summarized by the “S” curve. Generally, most roasting profile curves will follow this pattern and it gives a pretty good guide for beginners to understand the roasting process.
For your reference, below is a typical coffee roasting temperature chart which reflects the coffee roasting temperature and time.
Drop Temperature (DT)
Right before you load the coffee beans into the drum, the temperature sensor will hover at around 500oF (260oC) which is the internal temperature of the drum.
After you load the drum with coffee beans, you will soon notice a drop in temperature in the sensor reading but do not panic. This is the point where the coffee beans are absorbing heat from its surrounding.
The burners at this phase will supply low heat to avoid burning the outside of the coffee beans.
Turning Point (TP)
As the coffee beans temperature rise and starts to reach thermal equilibrium with its surrounding, it will arrive at a Turning Point (TP).
From this point onwards, the coffee beans temperature will rise as it continues absorbing heat during the roasting process. The burners will go full power after the Turning Point (TP).
However, roasters have to be cautious here. Going too fast will cause poor development as the outside of the coffee beans will be well roasted but the center remains raw.
On the contrary, heating it too slowly will risk baking the coffee beans instead; resulting in hollow and flat tasting coffee.
Coffee Roasting Tip!
A good rule of thumb to follow is to allow the temperature to rise 10oC per minute. In technical terms, this is a 10oC Rate of Rise (RoR).
Roast Development (RD)
The Roast Development (RD) phase is a small window period during the roasting phase. During this phase, roasters have the flexibility to choose which flavor profile to feature in the roast.
Keeping the Roast Development (RD) short will preserve most of the acidity of the coffee beans. This is perfect for coffee beans with delicate flavors with roast profiles of Light Roast and Medium Roast.
On the other hand, lengthening the Roast Development (RD) phase will develop the body of the coffee beans. With this, you can expect more nutty, chocolaty and earthy flavors from the coffee beans.
Roasting is all about the balance.
Coffee Roast Profiles
Throughout the coffee roasting stages discussed, the roaster can pick different points in time to stop the roasting process. This depends on what the roaster intends for the roasted coffee beans to be.
For example, specialty coffee roasting will never set foot into the Second Crack zone since it eliminates all the natural flavors of the coffee bean. Instead, a Light Roast or perhaps a Medium Roast is more suitable for specialty coffee roasts.
If the roaster receives a coffee bean that has delicate flavors, the best way to feature them is to roast them to Light Roast levels. With this in mind, the coffee roasters play a crucial role in bringing the best flavors out of the coffee bean.
All in all, there are four common coffee roasting profiles:
- Light Roast
- Medium Roast
- Medium Dark Roast
- Dark Roast
FAQ On Coffee Roasting Stages
How long do you roast coffee for?
Air roasters and popcorn machines typically take 8–12 minutes, whereas drum roasters might take 14–20 minutes. Air roasters are able to roast the coffee beans with uniform temperature by floating the coffee beans on a bed of hot air. Comparatively, a drum roaster relies on a mechanical arm to stir the beans around to distribute heat.
How many cracks are there when roasting?
Two “cracks” are expected during a roasting process. The first one should occur at 196°C and the Second crack at 224°C. These popcorn popping sounds are good indications to tell the roaster the stage of the coffee roasting process. For example, at the Second crack, this indicates that the coffee beans are now rapidly approaching Dark Roast levels.
What are the 4 types of coffee beans?
Arabica, Robusta, Excelsa and Liberica are the 4 types of coffee beans which are most common in the market. That said, Arabica and Robusta coffee beans dominate 99% of the coffee beans supply in the world. Liberica coffee beans are slowly gaining traction in the South East Asia region due to the boom in specialty coffee popularity.
How soon can you use coffee beans after roasting?
Generally, most roasters recommend waiting three days to a week before you can use the coffee beans after roasting. This is to allow your coffee beans to release the trapped carbon dioxide gasses. If not, this can reduce the efficiency of the extraction process during coffee brewing leading to an unbalanced cup of coffee.
Closing Notes
That concludes the 6 coffee roasting stages that you need to know about. To roasting coffee process is a delicate art and I hope this post have shed some light on this topic.
Every stage of coffee roasting contributes to the coffee-drinking experience of the consumers. From the aroma to coffee-tasting notes, all of which will not be featured in the final cup of coffee if the coffee roasting process did not go well.
That said, the barista preparing your coffee also has the responsibility to prepare the espresso drink with
If you find this piece of article informational, please share it with your fellow friends. baristas and home brewers!
Happy brewing!
