Coffee roasting happens in several distinct phases, each marked by chemical and physical changes in the beans that shape the flavor, aroma, and color of the final coffee.
We have two main things to control: Time & Temperature.
We also need to monitor the rates of rise (steepness of the time/temp curve) during roasting .
Each phase will have a target time, temperature and rate of rise (ROR).
It's important to note events like when the colours of the beans change,
when they start to change their smell (things like bread or sweetness) or when we reach first crack, etc.
It's helpful if you write down the temperatures (every 30 secs).
While terminology can vary slightly among roasters, here are the main phases commonly recognized:
Notice that the ROR tends to descend as we progress through the different phases.
That is the ROR gradient for the browning phase is gentler than the drying phase.
☕ 1. Drying Phase (Endothermic)
Temperature range: ~100°C–160°C (212°F–320°F)
Duration: 4–8 minutes (depending on roast profile)
Green coffee starts with about 10–12% moisture.
Heat is applied to evaporate this water without burning the beans.
Beans turn from green to a light yellow and begin to smell grassy or hay-like.
The roasting environment absorbs energy (endothermic process).
Goal: Properly remove moisture to prepare beans for chemical reactions in later stages.
Don't rush this phase or the inside of the bean may not get evenly dried
🌾 2. Maillard Reaction Phase (Browning Phase)
Temperature range: ~160°C–190°C (320°F–375°F)
Sugars and amino acids react (the Maillard reaction), creating brown pigments and complex flavor precursors.
The bean color deepens from yellow to light brown.
Caramelization and sweetness actually start to develop when beans turn yellow.
Caramelization = applying heat to the natural sugars inside the coffee beans to bring out sweetness.
Amino acids are what give acidity when they are heated.
Aromas shift from grassy to toasty, nutty, and bread-like.
Internal bean pressure starts building as gases (CO₂, water vapor) form.
Goal: Develop the foundational flavors and aromas that define the coffee’s character.
Timing this phase is very important ... its must not be too fast or too slow.
Too Fast:
It is important not to rush this phase or the coffee can turn out too bitter or tart.
Or if this phase is rushed, the caramelization or acidity may not form.
Too Slow:
The chemical reactions become muted and we loose acidity ... we end with a bitter/flat/baked coffee
🌋 3. First Crack (Exothermic)
Temperature range: ~196°C–205°C (385°F–400°F)
Internal pressure causes the beans to crack open audibly.
This marks the transition from endothermic to exothermic — the beans release energy.
The coffee expands in size, and oils may begin to migrate toward the surface.
Goal: Achieve the first clear milestone of roast development — suitable for light roasts.
🌑 4. Development Phase (Roast Development Phase)
Temperature range: ~205°C–220°C (400°F–430°F)
After the first crack, the roast can be stopped or continued depending on desired profile.
Caramelization and pyrolysis intensify, creating sweetness, body, and deeper flavor.
Roasters control time here carefully to balance acidity, sweetness, and bitterness.
The longer you go into this stage, the less sweet and acidity you will get and the more bitter your coffee will be.
The longer this stage , the more you are roasting out the sweetness & acidity.
Goal: Fine-tune the flavor — too short can taste sour/undeveloped; too long can taste bitter or smoky.
Here you can balance acidity (the fruit bomb) or sweetness
🔥 5. Second Crack (Optional – for Dark Roasts)
Temperature range: ~224°C–230°C (435°F–446°F)
Beans crack again (softer and quieter).
Cell structure breaks down, and oils appear on the surface.
Flavors become darker, more roasted, with smoky or even burnt notes if pushed too far.
Goal: Produce darker roasts such as French or Italian — bold, less acidic, more bitter.
⚙️ 6. Cooling Phase
Immediately after roasting
Beans are rapidly cooled (usually by air or water) to stop further roasting.
Proper cooling locks in the developed flavors and prevents over-roasting.
Would you like me to include a temperature/time curve diagram showing these phases visually? It’s a great way to see how roast development progresses.
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Roasting with sight and smell
Things to watch for if you are roasting without any temp probes:
Track the progression of the roast by looking at the bean colour.
We start with a dark green shade.
When it gets to the drying stage it changes to a yellow.
When the beans go "full yellow" we have reached the end of the drying phase.
When the beans are green you often smell "wet grass".
As they dry you smell "dry grass". You will often smell "sweetness".
The next stage is the browning stage. You will smell "baked goods", like biscuits straight from the oven.
You will also see that the beans are larger in size. They swell as they dry.
So they should occupy more "height" or volume in your roaster.
The beans are also lighter, so they should be thrown higher in the roasting chamber.
We are approaching 1st crack. You might smell vinegar/ acid.
If you like fruity, citrus, floral notes drop the coffee just after 1st crack.
If you like more chocolate, caramel, sweet notes, continue roasting.
You should see the bean mass really moving as they are much lighter
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