This post has some basic info on how to create profiles and roast coffee that
should get you started on this journey which will teach you so much about coffee.
Colour of the roasted bean.
This is a good place to start.
The colour of the coffee beans can range from an almost yellow color to a deep black.
The roast level is going to have a huge determining factor on how that coffee tastes.
The color of a coffee roast is a direct indicator of flavor, with lighter roasts being more acidic, fruity, and complex, while darker roasts are bolder, more bitter, and smoky. The roast color is the result of the roasting process, which uses heat to create chemical reactions that develop new flavors: lighter roasts have gone through fewer of these changes, preserving more of the bean's original characteristics, while darker roasts have undergone more browning and caramelization.
Light roasts (light brown to cinnamon)
Flavor profile: More acidic, brighter, and can have floral, fruity, or citrus notes.
Characteristics: Preserves more of the original coffee bean's characteristics. Acidity is more prominent.
Why: Roasted for a shorter time, often up to "first crack".
Medium roasts (medium brown)
Flavor profile: Balanced, with a fuller body. Flavors can include sweetness from caramelization alongside some acidity.
Characteristics: Less acidic than light roasts, with a smoother, more balanced flavor. The surface of the bean is typically not oily.
Why: Roasted longer than light roasts, allowing for more sugar browning and caramelization.
Dark roasts (dark brown to black)
Flavor profile: Bold, full-bodied, and can have notes of dark chocolate, nuts, toasty or smoke.
Characteristics: Little to no acidity and may have a slightly bitter aftertaste. The surface of the bean will be oily.
Why: Roasted for the longest time, with extended heat causing the natural sugars to caramelize and leading to more roasty, smoky flavors.
But roasting is so much more than just the color of the coffee beans.
Find a good supplier of raw coffee beans
Probably the most important factor going into your roast is the quality of
the green coffee beans. Your choice of green beans is super important.
Coffee beans are actually a seed that grows within a coffee cherry which is a
fruit. The beans could be grown at anywhere in the world between 600 and
2500 meters above sea level.
Plus, different growing and processing methods will have a huge impact on flavor.
So finding good importers is very important.
The first part of the selection process might be the country of origin but bear
in mind that different farms within the same country can have radically different flavors
depending on a lot of things including the processing method.
Keep in mind the processing method used in the country of origin and the age of harvest.
If you notice that the green beans you buy don't have a strong flavor or smell it could be that they're not
being properly stored by the importer .
Just order small amounts of coffee from new suppliers first and see how this goes .
Processing Methods
There are many different methods but these are the most common ones:
Natural
The natural process is where the coffee cherry is laid out in the sun (usually in a warm
dry country where the coffee is produced). After a few weeks the cherry will come
off the coffee by itself when it's reached a certain moisture content.
These sort of processes often give a natural fruitiness.
Washed
The washed process is as the name implies when the coffee cherry is washed off the beans
and the beans are left out in the sun to dry without the cherry.
These processes have a really big effect on how the coffee is going to taste.
With natural processes tasting more fruity and earthy because they've been in contact with the cherry for longer and with a washed process tasting more clean and sharp.
Honey
The honey process is where the beans are de-pulped through a machine and then left out with the mucilage still on, in the sun or in a greenhouse. to naturally ferment for a few weeks until the bean reaches a certain moisture content. Depending on the conditions, you can get a really interesting middle ground between a natural processed fruitiness and the clean sharpness of a wash process.
Carbonic Maceration
Carbonic maceration is where the beans are put into an airtight container with
carbon dioxide pumped in to prevent oxidization. This leads to a kind of anaerobic fermentation that brings out some really unique flavors in coffee without the sort of mustiness that can
come from other processing methods .
Structure of a Roast
A standard roast will look something like this graph.
It includes key markers like the start time, the first and second "cracks" (popping sounds), and the final temperature and time.
While a universal curve doesn't exist, roasters use these graphs to control flavor development by creating a repeatable process that can be customized for different beans.
The shape of this curve whether it's long and thin or short and sharp will completely change the taste of any coffee.
These are the different phases of roasting:
Charging
At the start of the roast we have the charging phase.
This is when the beans go into the roaster.
But before we add the beans we need to heat up the machine to a good temperature
(called your charge temp).
Don't start from zero. You want to heat your roaster and idle at the temperature you intend to use for initial heating for at least a few minutes before you put the beans in.
As soon as the beans go in you'll see the temperature drop due to the cold beans going in and absorbing a lot of the heat.
Depending on your roaster and batch size you'll start your roast at at least 170 degrees C
(340 Fahrenheit).
The charge temperature can vary from machine to machine.
The bigger the batch of coffee you're using, the higher the charge temperature should be.
So for example with a 100g roaster I usually start at between 170 to 190 degrees C
but for something bigger (like the Aillio Bullet) which is a one kilo roaster I might start
somewhere between 180 and 200 degrees C
For a very large roaster at commercial scale something like 10 to 20 kilos it's safe to go up to 210
degrees C as there's a big enough mass of green beans to absorb the heat without burning the beans.
Ideally your machine will have a temperature probe inside and a way of tracking this on a graph .
Without a roasting graph it's pretty hard, though not impossible to achieve a good roast
and especially to replicate that roast.
The roaster temperature (air or drum temp) might be 200–250°C, but the bean mass takes time to catch up due to thermal inertia. The speed at which cold raw (green) coffee beans rise to the temperature of your coffee roaster depends on a few key factors like the Roaster type, Charge temperature, Batch size, Roaster power & airflow
There are three main types of heat transfer in roasting:
a. Conduction (direct contact with hot surfaces)
b. Convection (hot air)
c. Radiation (infrared, etc.)
If you're using a fluid bed roaster (like a popcorn popper or hot-air roaster), the heat transfer is mostly convection, and the beans heat up faster.
If you're using a drum roaster, which relies more on conduction and convection, heat-up is slightly slower but more even.
🎯 Rule of Thumb
If you charge at ~200–220°C:
Beans typically reach 100°C within ~1–2 minutes
They’ll be close to roaster environment temp (~200°C) within 6–8 minutes, depending on batch size and airflow.
Turning Point
The point at which the temperature stops dropping and starts going up is called the turning
point.
I keep the power of the roaster to around 50% until the turning point so that the heat
doesn't go into the beans too quickly.
Letting the beans come up to temperature in a more ambient environment avoids
damaging the beans.
Once we hit the turning point at between 30 seconds and one minute of roast starting that's when I turn my heat up.
Learn what your roaster can do and find the upper limit of how much temperature you
can push without burning the beans.
Depending on the machine you have the power grade will be different.
For my small induction heat roaster I turn the power up to 95% but if you're using
a gas roaster 100% will probably be too much power and you'll end up
burning or scalding the beans .
Yellowing Phase
As you roast, the beans will turn from their natural greenish color to a yellow (and
eventually start browning). This is sometimes called the "Dry End" phase
The yellowing phase progresses to the browning phase where
the moisture is low enough for Malliard reactions to start taking place (and
interesting flavors and aromatics start coming out of the beans).
First Crack
The next thing you'll be listening for is the first crack. This is where the pressure
buildup of gases will break through the structure of the coffee beans making a popping sound.
This is where the so-called development time begins (though this is a bit of a
misnomer as development occurs throughout the roasting process).
The longer the roast goes on the more caramelization occurs. You'll get more sweetness, body and
richness but this will be at the cost of the beans unique flavor.
Second Crack
As your coffee gets darker it will get more bitter and oily as the roasting process continues.
Eventually all coffees will burn and become pretty indistinguishable from one another.
I recommend keeping your development time to between 15 and 25% of your total roasting time.
Drop
At the end of the development phase, we have what is called "the drop".
This is where you remove the beans from the roaster and you start cooling them quickly.... ASAP .... ideally within four minutes to stop the transference of heat.
Once the roast has reached the desired level you can remove the beans from the roaster to stop the
roasting process.
This is know as "dropping the beans" and the associated temp is called the "drop temperature".
More than color, this is probably the best indicator of the final roast level.
Now all of this can happen in a short or long amount of time which will give
drastically different flavor results. .... which leads me on to coffee roasting speed
Roasting Speed (Total Roast Time)
The speed of the roast is super important and if you roast your batch really quickly in general
this is going to emphasize the innate characteristics of the bean.
If you're roasting for pour over or to accent fruity or floral notes you'll probably want to roast a little
bit faster.
This means using higher temperatures especially early on in the roast and dropping the beans earlier.
Different kinds of roasters will operate at different speeds.
For example fluid bed roasters can heat coffee a lot more quickly than drum roasters without
the drawbacks of transferring too much heat to the bean too quickly (which can
result in scorching or tipping which is where the beans or the edges of the beans get burnt)
You can slow down the roast by lowering the initial temperature and the rate of rise (which
will lead to more caramelization & sweetness).
In his books about coffee roasting Scott Rao talks about how a smoothly declining
rate of rise is generally preferable for good coffee .
The rate of rise (ROR) is an indicator of how quickly the temperature is rising.
You want a relatively fast the rate of rise in the beginning of the roast as you push through the drying
phase but you want to slow that down gradually as you enter the development phase
to give the beans more time to caramelize without burning them.
If you just power through your roast at 100% you're likely to get burnt beans and you'll have
craters appearing after the first crack.
(Craters are what happens when heat escapes from the beam too quickly and creates these small holes
as they break through the structure of the beans).
So you'll want to slow down your roast in advance of the first crack .
This is why you need to gradually step by step lower the gas or power of your roaster.
I usually increase the temp in smaller steps as I want to keep the temperature increasing
(but at a slower rate) as I enter the development phase.
-----------------------------------
have the beginning of the "drying phase".
This is where the beans will lose a lot of their moisture.
This often occurs between four and eight minutes (depending on your roaster).
You usually start the browning phase after this , which is where the beans become sweet and aromatic.
Once we reach the first crack where you hear a popping sound .
We now enter the "development phase" which is where the beans caramelize and add sweetness and body at the cost of high notes and aromatics.
If you continue the roast that you'll reach the second crack where the structure of the
bean really starts to degrade and you end up with toasty, smoky and even burnt flavors.
These are characteristic of darker roasts.
You have to do this carefully though because you don't want the roast to stall or crash.
Look at this roast curve here that dip in temperature right after the first crack is a crash.
It will probably make this roast taste less clear and exciting than without it.
In this case maybe the bean wasn't very dense and the heat coming from within
the beans wasn't enough to continue heating each other.
Stalling is where it takes too long to reach the first crack
You really really don't want this.
This means there isn't enough heat in the drum or coming from the beans
endothermically to continue the roast and it will end up with coffee that tastes unpleasant ...
even stale. It's not really possible to recover a roast that's stalled midway through so you'll
want to plan your roasts properly and get to know the beans that you're using this is why a lot of professional roasters use a sample roaster to test the beans before they go ahead and put
10 kilos into one of their big roasters.
This is more common with certain beans than others so be sure to test them out
and do a few different styles of roast and taste them side by side with a
cupping to compare.
Cooling, Storage & Blends
Once you drop your coffee beans you'll want to cool them as fast as possible.
you also need to leave your beans to degas
or lose the co2 from roasting for at least a few days before you store them
leave your beans for at least a week or so before you use them for brewing
---------------------------------------------------
when roasting coffee beans is the temp inside the drum roaster different from the temperature of the beans?
Yes, the temperature inside the drum roaster is different from the temperature of the coffee beans, especially at the beginning and throughout the roasting process.
Here’s a breakdown of what’s happening:
🔥 Drum Temperature vs. Bean Temperature
Drum temperature (also called environment temperature or air temperature) is the temperature inside the roasting chamber — including the air and drum walls. This is usually measured by a thermocouple placed inside the drum, but not in direct contact with the beans.
Bean temperature is measured via a bean probe in direct contact with the beans. It shows how the beans are absorbing and reacting to the heat.
📈 Temperature Differences Over Time
At Charge (start of roast):
The drum temperature is much higher than the beans.
For example, the drum might be 400°F (204°C), while room-temperature beans are around 70°F (21°C).
When beans are dropped into the roaster, the bean temperature drops initially (a dip called the turning point), then begins to rise as the beans absorb heat.
During Roasting:
The drum/air temp remains higher than the bean temp.
The beans gradually catch up, but usually lag behind by 20–80°F (10–40°C) depending on the stage and roaster design.
Near First Crack:
Bean temperature is typically around 385–400°F (196–204°C).
Drum temperature may be higher or adjusted downward depending on roast style.
⚙️ Why This Matters
Controlling roast profile: You need to monitor both temps to shape the roast (e.g., development time, first crack timing).
Avoiding scorching or tipping: If drum temp is too high relative to bean temp early on, surface damage can occur.
Heat transfer methods: Different roasters (drum, fluid bed, hybrid) transfer heat via conduction, convection, and radiation — the relationship between bean and drum temp varies accordingly
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