Roasting basics

This is basics about roasting in general.

I (Therese talking) started this roasting guide, because in 2016 we were a bunch here in Denmark who got the new Bullet R1 coffee roaster. It’s a 1 kilo roaster with many setting possibilities and data output. Since it was new, we had to explore and learn together. This made me collect info on this site. But of course, much of it can be used on other roasters too.



Scope of the roasting process
Preheat temperature
Bean characteristics
Bean temperature (BT) & Turning point
ROR curve
Development time (DT) & Roast degree
Weight loss
Fine-tuning the roast profile
Taste is king

When you got hold of these basics – you can move on to Roast Profiles


Scope of the roasting process

When you roast coffee you want to get the best taste developed in the coffee beans and avoid bad taste.

The first two things you should focus on when roasting coffee:
1) The way the temperatur rise, not too slow/not too fast heating of the beans
2) Determine when to stop the roast


1. Even development
It takes time for the heat to travel from the surface to the core of the bean.

If the heat is too high during the roast you risk scorching of the beans = the outer tipping-in-beansof the bean get roasted quicker than the inner = you get both burnt AND underdeveloped taste.

If the heat is too low you will not get enough development of the taste. The aroma is flat. This roasting flaw is called baked.

How do I know if the coffee got too much or too little heat ?

First Crack (FC)
When roasting coffee at some point, the beans start to crack; they expand and make a noice like breaking a tree branch (like popcorn, listen here). When the first craking is over, its silent for a while, and then starts a second crack (SC).

The time to First Crack (FC) starts depends on how much the beans are heated.

If the beans hits FC at 5 minutes, it’s too quick. Aim for at least 7-8 min.

If the beans hits FC after 12 minutes, it’s too slow.

Late FC gives a weaker crack = more difficult to hear.

When I roast coffee, my aim is to get a First Crack (FC) start around 8-9 minutes but thats for a light roast of high grown beans. For darker roasts and espresso, I go for 10-11 minutes.


2. Stopping the roast
roaster-door-dump-sh2During the roast chemical compounds are formed and broken down all the time. So the point where you stop the roast is very important for the taste.

Coffee people typical have a strong preference for roast degree: either light or medium or dark – or burned-black dark as hell. There is no common definition of what exactly is medium or dark roast.

How do you determine when to stop the roast ? There is no ultimate technique, because the development of the taste i multifactorial. I use the time from FC start. Some look at the bean temperature. Others go by the smell of the roast.

survey-when-to-stop-roast-27decI asked a coffee roaster forum on Facebook what they go by. Here is what they answered – I only gave them possibility to make one tick: which is the most important ? Many commented that they look at several things.


I have started a podcast about coffee roasting. The first episodes are about the different approaches to stop the roast.


Preheat temperature

How the beans are heated not only depends on the power-setting during the roast, but also the preheat temperature. And for how long; how well the roaster is heated (else the heat will not only go to heating up the beans but also the metal of the roaster).

Choose the preheat temperature according to batchsize (grams) and depending on when you want to reach First Crack (FC).

The preheat temp has a big influence on the roast – its like the initial push of heat, like a push of a boat in water. The speed of the heat transfer into the bean depends on the temperature gradient from the outside to the core.

Too low preheat temp will give a too late FC time. You cannot catch up during the roast by using high power (like P9).

Too high preheat temp will give a too soon FC time / scorch the beans = roast the outer of the bean quicker than the inner. A FC start before 7 minutes is too soon.

I prefer a FC start around 8-9 minutes (Therese speaking) for light roasts – and 10-11 minutes for espresso and darker roasts. I know others who are content at 11-12 minutes. Late FC gives a weaker crack.


12 batches, all 500 grams – roasted by Steffen, starting on P8 and then declining.

The graph shows FC start around 9 min with 170°C and around 8 min with 180°C. Clearly other things are affecting too, like type of bean.


Our experience with the Bullet

400 grams batch: At least 170°C (in combination with P7-6 and Fan2-3) or 175°C, to reach FC around 7-9 minutes.

500 grams batch: 170-180°C. Steffen gets FC start around 9 min with 170°C and around 8 min with 180°C with power starting at P8 and then declining.

7-800 grams batch: 190°C

1000 grams batch: 195-200°C. Jens gets FC around 9 min with preheating at 195°C and P9.

But the room temperature also makes a difference. We live in Denmark where it’s cold most of the year.

More data is welcome. Please send in.


Preheat time

Its not enough that the Drum temperature reads the set-temperature – because it takes time to fully heat up the roaster. Thats why it takes a while before the Bullets says “Charge”.

I like the preheat time to be at least 25 minutes. Steffen use 45 minutes of preheat.

Its a common experience in coffee roasting that the first batch is a bit slower than the following batches. Thats because the roaster isn’t fully heated to begin with.


First important is the preheat temperature … then the power during the roast has influence on how long it takes to reach FC.

There is a general consensus to: Decrease power in the latter part of the roast.

When the beans start getting brown, turn the heat down gradually.

Kaffe-Thomas developed this recipe: after 5 minutes decrease P one step every one minute.

Morten Münchow says: ROR-level around 10 in the middle of the roast and around 5 from when First Crack starts.

See further under Roast Profiles.


Fan/ airflow

You can have airflow at one setting during the entire roast (like on F3). Or you can increase airflow during the roast to blow out smoke and chaff in the end. If you airflow is too high to begin with the beans will get roasted quicker on the outside than in the core.

We have seen different patterns in what happens to BT when increasing Fan.

At 400 grams I have seen a shift a F5: First when increasing Fan the heat transfer increased (like applying heat with a hairdryer). But from F5 it cooled the roast. This probably depends on batch size.

Also, wether the filter in the chaff collector is clean or full of chaff and oils will make a difference to the airflow in the drum.

Here is the cleaning routine for some of the Bullet owners:


Note: Aillio is working on a new design of the chaff-filter.



Use at least d6.

We are still exploring. A general recommendation is larger batch needs higher drum speed.

Here Klaus has registered what the drum speed setting on the Bullet corresponds to in rounds per minute (rpm) – he counted it manually: putting a white mark on the drum and then counting the rounds within a minute.

Kaffe-Thomas observed that increased drum speed gave a rise in ROR. Where as Steffen observed a decrease. The difference might be because of difference in the fanspeed or stage of the roast or …

More data is needed.

Bean characteristics

The heat needed to get nice development depends on the characteristics of the beans.

Larger beans needs more heat. Harder beans (high density) needs more heat. On the other hand a small bean with low density should have lower heat to avoid getting burnt.

preheat-ifht-bean2The moisture level in green beans is normally 10-12%. If the moisture content is low the beans get burnt much easier – so reduced heat is necessary.

Joe Marrocco have written a blogpost about bean density

Bean temperature probe

The Bullet got a temperature probe to measure in the middle of the bean pile. You can feel it by sticking you hand inside the left side of the door window – its placed above the window.

Important know: Bean temperature (BT) measurements are not comparable from roaster to roaster. The probes varies. So you cannot use that FC starts at 200°C in one roaster. In another roaster it can be 180° or 207°C. Also read about this on the Scott Rao blog – under the post; Your bean probe has been lying to you

You just have to get to know your own roaster.

ROR curve

ROR = rate of rise = temperature rise of the bean probe per minute
Calculated during the roast.

Bean temperature: Turning point

“Turning point” (TP) is an artificial point on the ROR curve. It’s the low point shortly after the roast has started. Its typical around 1-1,5 minute in.

The initial drop in Bean temperature (BT) is a mix of temperature in the bean probe before adding the beans and the temperature of the beans (room temp). So to beginn with the beans are cooling off the bean probe. As the beans get heated up at some point they make the BT probe rise again.

The time and temperature of TP says something about the speed of this initial “push” of the heating up process.


This graph is 12 batches, all 500 grams, roasted by Steffen. They were not that different in power and fan setting during the roast.

X-axis is the TP temperature and Y-axis is time for FC start.

This plot shows the tendency to higher TP temp gives a shorter time to FC start.


As the roasting proceeds the beans will go from green to yellow to brown – in various degrees.

You can note down when the beans are at yellow as a mark on the roast. Its when all the green is gone and before they start getting light-brown.

If yellow comes too early, like before 3 minutes, the outer of the bean is getting roasted quicker than the inner. And its too slow when later than 6 minutes.

Rob Hoos has written a book on Modulating the Flavour Profile of Coffee . He introduces talking about the importance of the stage from yellow to first crack – the midle phase between drying and 1st crack. He calls it the Maillard phase.

If you would like to get at later yellowing point, you can use “soak” in the beginning. The first minute set the heat at P2, then graduatly rise to the higher heat level within a minute. Note: here soak has nothing to with adding water.


Development time (DT)

DT = Time from FC starts and to drop/end of the roast.

Its not that easy to determine exactly when First Crack starts. Read more here How to determine FC start

Roast degree

The longer DT, the darker a roast.

But the temperature rise during DT also makes a difference. If temperature rise is low, the darkening of the beans will be slower.

At some point Second Crack (SC) will beginn. This sounds weaker than First Crack.

I know many roasters who stop right at the first sounds of second crack – its called “on the verge of second crack”, so before SC is really going. This roast degree is called Full City.

Very dark roasted coffee is roasted into Second Crack – several minutes. Here the oils will come out to the surface of the beans. This roast degree you find at Starbucks and in Italy.

On the other hand light roasts is stoppede before First Crack has ended. BUT there is no common definition of when its a light roast or medium or dark. Here in Scandinavia what we would call a medium roast is a light roast in USA.

Fil 12-12-2016 10.14.41


Stop the roast

During the roast chemical compounds are formed and broken down all the time. So it’s very important for the taste when the roast is stopped.

You have to search to find the optimum for the bean at hand. Ten seconds earlier the coffee can taste underdeveloped and very acidic. Ten seconds later the coffee can taste flat or burned. While at the right timing the coffee has a big aroma and is nice balanced in acidity/sweetness/bitterness. Its different from bean to bean where this optimum lies. And a coffee can have several optimums – at different roast degrees.

But not only the time from FC onset determines the taste. The temperature rise does as well (ROR). A quick rise (like more than 7°C pr min) gives more acidity and clarity. A lower rise (2-5°) gives more body. Zero rise gives a flat taste (called baked).

How do you determine when to stop the roast ?
There is no ultimate technique, because the development of the taste is multifactorial. I use the time from FC start. Some look at the bean temperature. Others go by the smell or color of the bean.

survey-when-to-stop-roast-27decI asked in a coffee roaster forum on Facebook what they go by. Here is what they answered – I only gave them possibility to make one tick: which is the most important ? Many commented that they look at several things.

I have started a podcast about coffee roasting. The first episodes are about the different approaches to stop the roast.

Shape of the ROR curve

It’s a general principle that after the initial drop and rise of the ROR curve (whitin the first 4 minutes) – the ROR curve should be declining.

Dont overfocus on getting a nice declining ROR curve. So many other things are more important.

But avoid the ROR curve going beyond zero (=BT is falling instead of rising) – and avoid ROR dramatically rising in the last part of the roast.

A rule of thumb is aiming at a ROR of 10-15 degrees per minute before First Crack (FC) and around 5 degrees per minute from when FC starts (say 2-6°C pr min).

The roasting consultant Scott Rao have propose some theories about a constant declining ROR and a development time ratio of 20-25%. Read his elaboration of this on his blog

For many new Bullet-owners this is the first time they get a graph with a ROR curve of the bean temp. So they focus solely on how the ROR curve looks. But a nice ROR curve alone wont make it taste good, if roast was too long or too short (when did FC start and how long was DT).

See graphs and read about working on the ROR curve in


When you stop the roast, fast cooling is necessary.

Aim: Get below 40°C in 4 minutes.


Weight loss

If you weigh your roast before and after roasting, you can calculate the weight loss in percentage. This says something about how far the roast went: the darker roast the greater loss-percentage.

A light roast is around 11-13%. A real dark roast is 20-22%.

tipping-in-beansScorching and tipping

These are roasting defects caused by too much heat.
The picture here is tipping where the bean has got to much heat on the tips of the bean.



Here is a brazil bean with tipping. The ends has cracked open and are darker in color.

This is to much heat, too quickly.

Try lower preheat temperature. Aim at later FC start.




Read more:

and see pictures

Fine-tuning the roast profile

The taste is very much affected by small changes in the roast profile. There are a lot of advice out there on how to fine-tuning the roast profile.

But here you have to watch out … A rule of thumb that works on one roaster doesnt work on another … and there is differences in taste preferences … and there is theories out there that works in one context but not another. Beans are different. Roasters are different. Taste preferences are different.

You have to try out for your self.

Read experiences on the next page

Taste is king

The only thing that determines the success of a roast is how it tastes.

For every roast make notes of the taste. This is the key to improve your roasting skills – and a lot exploring and trying out.



Therese tasting coffee at the World of Coffee event in Sweden, 2015



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