Bean probe sensitivity to airflow

The bean probe do not only measure the temperature of the beans. Here I have tested the sensitivity to airflow.

It’s on my Bullet R1 roaster and a test roast with old beans, not meant to taste good. The bean probe is a NTC precision type

Look at the graph after 8 minutes:

Peru test ny probe sept2017

In the last 4 minutes of the roast I jumped between a high airflow; F7 and a low; F2 (and once F1). Each time approximatly 30 seconds stretch. I chose F7 because already at F5 the airflow starts to cool rather than increase heat transfer. That is with 400 grams batches – at larger batches it takes higher fansetting.

High airflow made the ROR go negative within 10 seconds.
Low airflow made it go positive within 10 seconds.

During this shifting airflow the Bean temperature (BT) did anyway rise from 187 to 191°C, measured at low airflow. Probably due to heat transfer from the drum, where the heat setting was constant at P3 during these 4 minutes.

Data excelark

Clearly the bean probe is not only affected by the actual bean temperature – but also of the airflow. As we long expected. And as Rob Hoos also wrote in his Roast Magazine article this month (the sep/oct 2017 issue).

And the bean probe is quicker affected by the airflow than the beans (metal do absorb heat quicker than the cellulose chunk beans).

Read more about the Bean Temperature under Roasting Basics.


Note: The first 8 minutes of the roast was because I had just changed the bean probe. At first the test was only to see the difference to the old one. But during the roast I got the idea to test the airflow impact on the BT reading.

High heat start

Our roasting community here in Denmark is exploring a new approach on the Bullet R1 roaster.

15 of us were on a roasting course with Michael de Renouard from The Factory Roast Lab Copenhagen. He is a roasting consultant and travels the world teaching coffee roasting. In his own roastery he is roasting on a Loring. He roast quite light.

Refshaleoen kursus maj2017

Michael tried out the Bullet roaster. He thought it did well; no burned or smoked taste in the beans. And its possible to get the beans heated quickly. He likes that you can control heat and airflow separately.

He found that you could start out with high heat without the beans got scorched/burned. Preheat 200°C for a 700 grams batch and then P8 – leaving room to step up to P9 at then end of the ROR peak.

But this was for high density beans (high grown). Be aware that lower density beans, like brasil, need a lower preheat temperature. Steffen got a Costa Rica bean which gets burned if the preheat is more than 170°C.

The high heat makes a fast start on the roast. But if it doesn’t scorch the beans, then no problem. Michael focus on the lenght of the phase from yellow until First Crack start. Here he aims at 3 minutes and at the same time aim to bring ROR below 5 for the First Crack phase. To do this the heat must be turned down markedly.


Exploring the difference

Here Thomas Villars used the strategy on a etiopean bean. He thought it tasted better than earlier roasts of the same bean. Despite FC starts as early as 5:23 min.

New strategy:

Villars Homa rist 13majIn general a fast roast like this gives more “clarity” in the taste – and less body. Here the “middle phase” – from yellow to FC start – is 2:15 minutes long. It should give more body to prolong this phase.

Earlier Thomas roasted the same bean like this:

Villars Homa 30apr

Update 2 months later:
Thomas has continued this new strategy. He like his coffees better now.


There are many approaches in coffee roasting. Don’t take this website as the only way to do it. Just take it as inspiration – and explore for your self what suits your taste.

Repeating a roast profile

If you made a good roast, you likely want to repeat it 🙂 But thats not easy to do accurately because so much influence a roast.

Steffen from KaffeRist do it often. Here he made 7 repeated roast of the same bean – trying to make the same roast profile. All done in a row.

You can see how the curves doesn’t overlay completely. And First Crack (FC) starts at different times and temperatures.

Steffens 7 gentagne rist april2017

He roast on a Bullet R1 roaster. The software got a PlayBack function that repeats the settings of preheat, power and fan during from the roast you want to repeat.

But the same settings doesn’t give the same profile even though it’s the same bean and the same batch size. So during the roast Steffen overrules the automatic settings. The ROR curve is the best way to see where the Bean temperature (BT) is heading – to adjust in time.

And then he listens for the First Crack (FC) start every time. And aim to make the development from FC start the same every time: regarding time and temperature rise.

Good and bad tasting of the same bean

Here is an example of a good tasting and bad tasting coffee of the same bean. Much in the roast profile are alike, but not all the way. What causes the difference in taste ?

The bean is a washed arabica from Uganda. Fairly high grown at the Mount Elgon mountain on the border to Kenya.

The good tasting, 400 grams, by Therese

mt-elgon-great-2016-11-21-05-29-00Taste: no burn flavour, no bitternes, nice round and big aroma.

I roasted it again 9 days later. First the the curves were very close. But after 5,5 minutes the ROR levels differed. Here both curves:

Two roast of the same bean Mt Elgon nov2016

The higher ROR level here gave an earlier FC; at 7 minutes in the second roast where as the first had 8:45 min.


This coffee didn’t taste good to me. It had bitterness and burned taste. And a weak aroma = boring coffee.


What could be causing this difference in taste ?

Alike elements
The development-% was around 24% for both (the time after FC related to total roast time). And weightloss was about the same: 14,3 and 14,5%

Development time (DT) was 2:44 minutes for the good one. The bad with more burned taste you would expect to be roasted longer, but no, its roasted a bit shorter: the DT was only 2:19 minutes.


3 possible explanations for the burnt taste

(1) A higher temperature rise in the bad one: 12°Celcius (and BT ended on 181°C) … where as the good one only rose 6-8°C (to end-BT at 175°C).

(2) When entering First Crack the bad one had a ROR around 10°C pr min. Whereas the good one was around 5. I have heard a recommandation around 5°C per minute – and not as high as 10°C when entering FC and for the rest of the roast.

(3) The american roaster Rob Hoos talks about the importance of the middle phase: from yellow point to FC start (see his book “Modulating the flavor profile of coffee“). He calls it the Maillard phase. In these two roasts the drying phase up untill yellow point are not that far apart: 4:00 and 3:45. But the lenght of this middle phase is 3 minutes for the bad one, and 5 minutes for the good one.

A roast consultant told me he prefers 3 minutes, so thats not criminal in itself. But maybe it suits this particular bean better with a slower roast; a longer middle phase and lower ROR levels during FC.


Martin Kjeldsen roast of the same bean

Martin Kjeldsen lives in different part of Denmark, but we got the same bean – and the same roaster, the Bullet. The bean is from Uganda from Mount Elgon (on the border to Kenya).

Martin have also roasted the bean several times. This is his best tasting batch:

500 grams, preheat 185°C


Martins bacth was roasted 2 minutes from FC start to end-BT at 192°C. My good one was roasted 2:45 min and to BT 175°C. But our bean probes do not measure alike. Notice the difference in FC starts: Martin at 182°C. Mine at 167°C and 169°C.


Read more under Roast profiles.

Adjusting profile by control points

beans-trier-sh1I have found a new approach to decide adjusting power and fan during the roast on the Bullet R1.

And I am thrilled 😀

Until now I have just tried to do what worked earlier. And then hoping it was right for the current roast.

When it didn’t work out, it was too late to do anything about it. Like a ship the roast takes time to change direction.

How the batch develops from a given setting is much affected by type of bean, batch size, ambient temperature, how clean the filter is and so on.

My hopes for this roaster were to be able to design the profile: ROR levels, time of 1st crack (FC), yellowing and so on … And to know what I am doing during the roast. Not having to repeat the same roast many times before I get to where I want.


So I got the idea to find control points that tells me where the roast is headed. So I can adjust the heat in time.

When the roast has reached BT= 115 C at a certain time, I know if its on time or ahead or behind – and I can adjust the heat to regulate.

ROR levels are the speed of the roast and predict the time to reach FC start and so on.

I analyzed a bunch of my previous roasts. Both the successful ones and the unsuccessful (acording to how I want to roast).
Successful ones = when FC start around 7-8 minutes
Unsuccessful = FC starts later than 10,5 minutes

I picked milestones along the roast: bean temperature and yellowing and FC. Then noted the time and ROR.


There was a clear pattern. The unsuccessful roasts had lower ROR, naturally. Not so clear at 115 C. But from 130 C and onwards.

With this list I then roasted 3 batches. What a difference it made! Now I had the feeling of knowing where I was headed and could adjust heating in time.

All 3 batches got a FC on 8-9 minutes. I got the ROR levels more where I wanted them.

I am thrilled 😀

I have posted my list under Roast Profiles. But its only a start. Surely it will be developed as I go.

Be aware: Our bean probes are different: so you can’t use my list if your FC onset isn’t around 170 C. Make your own list.


My strategy has developed since I started my control point guide in November 2016, see

This is for high-density beans = high grown (I haven’t investigated the threshold for this, but something like above 1.500 meters) and a light roast.

My bean probe may be different than yours, so you cant use the degrees directly – but this can serve for inspiration to make your own guidelines.

New strategy

A high heat start → higher preheat than earlier

To prevent to big a drop in ROR after the initial peak (at somewhere around 1-3 minutes), increase heat at this point

Already at 150°C; aim for ROR level around 3-5 at FC start (typical around 170°C with my bean probe) by slowly decreasing Power

Preheat for 400 grams: 185°C – but if its the first batch 190°C

Start at P6. At turning point go to P7. During the ROR peak rise to P8. Exactly how this is done depends on Turning point temperature, the ROR-level of the peak and the time for reaching 115°C and 125°C

Fan at P2 until yellowing point or just as browning starts then F3.

After yellowing point, around 150°C decrease power step by step. I adjust this according to:

Aim for ROR around 10 at 150°C . And at 160°C ROR at 8 and power stepped down to P4.

At First Crack start have power at P2 and have ROR around 5. During FC the ROR has a tendency to drop. Don’t worry too much about it. But try and keep ROR between 2 and 4. If ROR is to high try with fan at F5 or even F6.

If ROR is higher than 5 after FC start, then do a shorter time to drop.

 400 grams ethiopean (Homa)

Homa 25juni

ProfileTool for the Bullet roast data

Another of the Danish Bullet owner; Steen Hjelmstrand – has made this software to do more things with data from the Bullet roaster, than the RoastTime software from Aillio.

Steen have name it ProfileTool and you can download it for free from his website

Note: keep an eye for updates. Steen is continuosly developing the software.


Airflow and chaff filter

Its not only the fan setting that determins the airflow in your roast batch. Also the exit passage of the air makes a difference.

→ If it flows easily the airflow is bigger.

→ If the exit passage is somewhat restricted; the same fan setting will give less airflow.

If the filter in the chaff collector is dirty (full of chaff and coffee oils) the passage is restricted. There for regularly cleaning is a good idea.

See what routine Bullet owners got in the Bullet guide under Fan/airflow

This is what the first filter in Bullet looked like (in 2016). Now the filter is much larger.



Learning to roast on the Bullet R1

bullet-sort-hvidThe Bullet R1 is a 1 kilo coffee roaster from Aillio.

It hit the marked in the summer of 2016. It has several settings: preheat temperature, power, fan and drumspeed.

Thats more adjustment possiblities than other roasters in this price range. So here is a lot to learn.

Here in Denmark we have a community of 30 Bullet owners who explore together – learning how to steer the roasting process on the Bullet.



On this site I have gathered the knowledge and experiences in:

1. The basics of roasting and control functions

2. Roast profiles on the Bullet– at the top I suggested a profil to start out

If you want to contribute from roasting on your Bullet, please write an email to  therese (at) – you have to put the address rightly together yourself.

Link to the official manual for the Bullet R1 roaster.

This site was started in September 2016 and is still under construction.