Episode 6 in the podcast Coffee Roasting Navigated is with four roasters at the Danish Roasting Championship. Again I ask them about how they decide to stop the roast. But we also talk development times and more.
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:
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.
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).
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.
The smallest particles in coffee grind are called “fines”. First fines was said to attribute bitterness and bad flavors to the coffee. Now fines are considered important to make coffee taste great.
How can fines end up giving opposite taste impressions ?
I have long suspected it had to do with how the fines were situated in the grind: The fines can either stick to larger particles – or to other fines.
Each result in a different taste: when fines are attached to bigger particles they act as part of the large particle in the extraction and do not over-extract as when they are separate where fines only stick to other fines.
Here I have used a high heat start and aimed for a really low ROR at First Crack. This is inspired by Michael de Renouards approach (see High heat post) and Tony Jacobsen (listen to podcast episode 4).
Kenya beans are typical large beans with high density. So they can tolerate high heat – and maybe need more heat to develop the core ?
To achieve the shift from high speed in the beginning to low in the end – you have to turn the heat down well in advance of the first crack (FC).
I just roasted two batches of Kenya like this. Both roasts hit first crack around 7 minutes. Both have a Maillard phase around 3,5 minutes (from yellow to FC start).
The first one, 400 grams, has higher speed (e.g. ROR) going into FC.
DT (development time) was 48 sek and it rose 2,7 C.
Thats an avarage ROR on 3,4 during DT.
Number 2, 500 grams, has a lower speed/ROR.
DT was 1:49 min and it rose 1,7 C.
That gives an avg ROR at only 0,7 !
I was afraid ROR at 0,7 degrees pr minute was too low. But no, this was the best roast. A really elegant acidity. A nice body. Much more interesting than number 1.
I cupped them after only 2 days after roasting. Thats early in my world. But I had to ship off the 500 grams batch to a friend. So I just wanted to check if it was acceptable. Normally with Kenyans I let them rest a couple of weeks before opening.
How does the weather impact your roasting proces ? I have written about it in this post http://coffeenavigated.net/changing-weather/. But this is complicated stuff – many things influence. It would be great to explore further.
So, I have started this project to collect data more systematic (pilot phase in June 2017). There might be a difference depending on the type of roaster. And in some climates the humidity varies more.
Would you like to join ? It will help you to know your conditions better.
NOTE: It requires that you often roast the same bean so you have a baseline on how it responds to your heat setting. This makes you able to tell when it behaves differently.
And it does take some effort to calculate the air water content from the relative humidity. And dedication to make registrations.
If so, write me on: email@example.com
I worked out a google sheet where all participants can fill in data. The challenge is to make a set-up that isn’t too complicated AND to exclude all the other factors that affect the roast. This will be refine here in June 2017 with the first participans (5 have already started).
Preparation: mapping your weather situation
To evaluate when you got an extreme weather condition that affects your roast … you have to gather a picture of your “normal weather” or medium … so you can state “Today has more humidity in the air” and so.
We need both temperature and humidity.
Regarding temperature you probably already have an idea. I live in Denmark. Most of the year the temperature is between 5°C and 15°C. So 20°C is higher than normal and 0°C is lower.
The humidity is measured with a Moisture Meter. But it will only give the relative humidity. The warmer it gets the more water the air can hold. So 90% humidity at 25°C has a lot more water than 90% at 5°C. As this graph shows:
So, to find what is extra high or low air water content where you live … you got to get both humidity and temperature data … and then calculate the water content by looking a the graph or using http://planetcalc.com/2167/
How to find humidity levels for your locations:
Find the official weather station near you – where you can get both data from the day and historical data. Both temperature and relative humidity (has to be measured at the time and at the same place).
You can also use your own instruments to log these data. But good calibration is needed. Moisture meters can easily measure 15% wrongly. Therefor data from an official weather is better. But if you live to far away, it wont represent the conditions where you are.
Select days through out the year that shows the variation where you live. Pick a low and high humidity day on cold winter days … and in spring/autumn … and in different kinds of warm summer days. Pick more days from warm summer days because the water content varies more at higher temperatures (if its 25 or 30 C)
If you have little variation through out the year, maybe 10 days is enough. Otherwiese use more.
Insert the data for these days in the google spread sheet and calculate the absolute humidity. You can use this one http://planetcalc.com/2167/ It also takes in Barometric pressure, but it doesn’t have a big influence when being at the same location. But if you are located 3000 meters above sealevel this important to calculate the water content.
I have made an area in the spread sheet for this.
When you got a good representation of how the weather varies at your location – then you can evaluate the limits; what is low water content where I live/what is high.
Maybee you start with one set of limits but then as you collect data on how it impacts your roast – then you adjust the limits.
Recording roast days
Makes notes both of days when the roasts behaves normal and when you suspect it to be affected by the weather – or when the weather is very different from normal. To get a full picture.
The impact on the roast relies on your evaluation compared with how the roast normally responds to the heat settings (the baseline).
Important: you should be aware if the first batch on the roaster needs more heat than the following – so this is eliminated from your evaluation of the weather impact.
The impact on the roast split up in to stages:
1) The start of the roast – how quickly do it get to yellowing point or First Crack ? Did the batch need more or less heat ?
2) Around First Crack start – here it’s normally nessecary to turn the heat down in advance to avoid to much rise in temperatur. Did you need to turn it more down than normal ? or less ?
To simplify things only note if you need more or less heat – or if it’s within normal range. In the comments you can note more details. Please do.
Then get weather data; outdoor temperature and relative humidity. Again calculate what that makes in Absolute humidity; grams water per cubic meter (m3).
Mark if the temperature and humidity is high than normal by coloring the value red.
Mark if the temperature and humidity is lower than normal by coloring the value red.
It is well known that the weather makes a difference to the roasting process. The change of seasons. A clear sunny day versus rainy weather.
At first you should think that the temperature was the only factor. But more factors play a role – like humidity.
And each factor may influence different parts of the roasting proces. So it’s complex. And it easily gets confusing. It also depends on the type of roaster and ventilation.
I will not claim that I got hold of all factors affecting your roasting. But here I can mention some of the factors:
At first you should think that the temperature was the only factor. If the surroundings are colder and the air sucked into the roaster during it takes more energy to heat up your beans
Also, what temperature do your beans have before roasting ? Does your bean storage change in temperature ?
Bean storage temperature
If your beans are 25°C and you heat them up to 200°C in 8-9 minutes, that is an average of 20°C per minute. If your beans instead is only 5°C, then there is a 20°C more “road” to heat up till 200°C – so that will take an extra minute to reach.
But temperature is not the only factor – the humidity also affects the roast.
The roaster sucks in air from the outside during the roast. Even though you are roasting indoors the humidity / H2O content in the room is significantly affected by the weather outside.
The level of humidity in the air can work in two ways:
(1) If the air is already heated humid air will transfer heat quicker than dry air. Water molecules transfer heat more efficiently than other air molecules, which are mainly Nitrogen and Oxygen.
So, if you have any airflow in your roaster: Air with higher water content will transfer heat quicker.
Have you tried being in a sauna compared with a steam bath (also called Turkish Hamam) ? The steam bath is about 40°C, but the sauna is like 80-90°C. That’s because the heat in humid steam bath air will hit you much more efficiently than the dry sauna air.
(2) The roaster sucks in air from the outside during the roast. If the air is not heated up before entering the roasting chamber the humidity will compete with the beans for the heat. So; dry air will make a quicker roast than humid air.
It might also be a factor that drier air gives quicker drying of the beans because it removes water quicker from the beans.
Relative and Absolute humidity
But the air on a rainy day in summer doesn’t have the same water content as a rainy day in the winter.
Lets compare a humid day at 1°C and at 25°C.
The humidity is measured with a moisture meter also called a hygrometer. But it will only give the relative humidity.
Relative humidity is the amount of moisture in the air compared to what the air can “hold” at that temperature.
As you see on the graph below; warmer air can hold more water than colder. The x-axis is the temperature in Celsius. The y-axis on the left is grams of water per cubic meters (m3). The lines are levels of relative humidity.
When outside air is sucked into the roaster we need to know the absolute amount of water per volume air.
Lets look at high humidity, 100% (rainy weather):
At 25°C the air holds 23 grams water per m3
At 1°C the air only holds 5 grams per m3
So if its 25°C outside and 100% humidity, there will be 4,5 times more water in the air sucked into the roaster – compared to 100% at 1°C.
As you can see on the graph, the difference in water content is much bigger at 25°C than around freezing point. So, in warm weather changes in humidity makes a bigger difference: At 25°C a dry day with 30% humidity has 7 grams water … compared to a humid day at 90% has 21 grams of water.
You can see this on a cold glass of water. On a warm humid day quickly water will condense on the outside of the glass. Thats because the warm air contains a lot of water. But right by the cold glass, it gets cooled down and the reach “dew point” – and condense from water vapor into fluid water.
Dry or humid climate From the graph you can also see that this has biggest impact at higher humidity. Here in Denmark we got high humidity (often above 80%). But if you live in a low humidity climate (like in the desert), look at the 10% curve on graph: the water content doesn’t change much at different temperatures.
Calculate your absolute humidity If you want to observe this in relation with your roasting – you can either have a moisture meter in the room, close together with a thermometer … Or get data from an official weather station nearby.
And then calculate the absolute humidity – like with this one http://planetcalc.com/2167/ It also takes in Barometric pressure, but it doesn’t have a big influence.
Note: If you use your own moisture meter – good calibration is needed. Moisture meters can easily be 15% wrong.
How big the influence is depend on how much airflow you use. And remember the coffee beans also loose water during roasting; going from a water content of around 10% to around 2 %.
Experiencing HIGHER humidity making heating during the roasting process more efficient:
Roaster Morten Riiskjær roast 150 tons of coffee a year, both on a 12 kilo Probat roaster using gas – and on a 60 kilo automatic roaster (listen to him roasting by smell in the podcast from december 2016).
He says: “When the weather is both warm and humid – you really have to watch out because the roast quickly runs out of hand”. So he uses lower charge temperature and lower heat around First Crack.
Experiencing LOWER humidity making heating during the roasting process more efficient:
Bob Werby had been roasting a lot on his 1 kilo Bullet R1 for a year – when he changed the humidity levels in his house. Going from 60-65% rel humidity to under 50% using dehumidification Equipment.
This made the roasts quicker. With same settings and batch size he reached first crack at around 7:15 minutes at 47% humidity – compared to an average of 8:50 min to first crack with humidity levels above 60%.
A roaster told me about this impact on the roasting process:
A fan typically controls the airflow in a coffee roaster. The fan has speed settings. However, the amount of air that the fan moves does not only depend on the fan speed setting, but also depend on the backpressure from the rest of the flow path. So if you have a chaff filter or collector depleted with chaffs it gives more resistance to the fan and the airflow is lower.
And … if the outside air is denser (higher barometric pressure, higher water content) it gives more resistance to the fan and the airflow is lower.
I suppose how much the weather affects the airflow in your roaster depends on extent of airflow: If you roast with a low airflow it wont affect as much.
In general, lower water content in the air gives quicker drying … This should give a faster roast … But the question is if it has any significant importance ?
And roasters living in high altitudes say that affects the roasting too.
Somebody said that the gas burner is affected by weather conditions.
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.
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.
In 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:
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.
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.
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.
My podcast Coffee Roasting Navigated is about the different approaches in coffee roasting. We start by exploring the different ways to decide how to stop the roast.
In episode 3 it is about roasting to a certain color. We are at a roasting course with Morten Münchow from CoffeeMind. I have called the episode “Roasting by color” but Morten focuses on more than the bean color to make a good roast.
The onset of First Crack (FC / 1st crack) is an important control point in the roast of coffee. Rapid development takes place in the taste from here on. First crack is when the beans expand and make a noice like the crack of a thin branch.
But all the beans do not crack right at the same time. First one, then quiet, then another. But at some points lots are cracking. So when should you call the time ? Was it a 9:15 or 9:40 minutes ?
Another thing that makes it difficult is the background noice: the noice of the roaster and the beans hitting the drum. So its difficult to hear the cracks.
Try listen to this sound bite … Make you own notes before reading on
Some beans have a more clear FC start than others. A late FC (like more than 13 minutes) will tend to make a weaker crack. Low density beans tend to make weaker crack.
I asked in a roaster group on Facebook (click on the picture to see a bigger size):
Around 0:15 into the sound bite, I also was thinking: “is it starting now ?” But then it silenced, so No.
Then there is one clear snap around 0:55. But I need more of a roll of cracks to say that it has started.
So I would also say around 1 minute.
When you can’t hear the cracking
How well you can hear the cracking is different from roaster to roaster. Some roasters are so insulated that it is impossible to hear.
This is what I hear roasters then do:
-> smell the beans in the trier. At first crack comes a smell of vinegar.
-> look at the beans in the trier. When they crack they jump around.
You can also use some listening device to get the sound. On this photo I listen with a stethoscope. It only really works through air – and not on metal or glass window (because that will transmit all the other noices as well) . On this roaster I took out the trier and fittet the stethoscope on.
Photo by Morten Münchow, CoffeeMind.
Here is another device: earmuffs with a tube. This photo is from the roastery Holy Bean in Denmark. Bo Nielsen got them from CoffeeTools.
Research has been done on the sounds during coffee roasting by P.S. Wilson. In his article “Coffee roasting acoustics” he concludes:
> Near the end of the roasting process, sounds known as first crack exhibit a higher acoustic amplitude than sounds emitted later, known as second crack. First crack emits more low frequency energy than second crack.
When you get advice from other roasters … and in particular if you want to repeat a roast profile from others … its important to know their taste preference.
What roast degree do they prefer ? Do you prefer Clairity or a richer taste ? What kind of aromas ? How high acidity ? Sweetness ?
We dont like the same things in coffee. But also; we dont notice the same things in the taste ! So much is going on in the taste of coffee: we notice what we focus on.
Some immediately notice bitterness. If the coffee has any bitterness they dont like it. Maybe they like a light roast with clairity and fruit/flowers aromas. And dislike roasted or burnt flavours.
Others only like coffee with solid burnt flavours, but really dont pay attention to bitterness. That’s in the darker roast range. They find the light roast thin and missing what good coffee should taste like.
This is Henrik and me (Therese). He loves very dark roasted coffee – like they do in Italy.
I find it tastes like a car workshop and awful burnt. I dont like it. But its fun to explore some times.
Normally I roast quite light (from around 1 minute from 1st crack start). But I am not at the lightest end of the scale. Coffee roasters like The Coffee Collective here in Denmark and Tim Wendelboe in Norway are a bit lighter than me – and they like more acidity.
Photo by Ida Kofod from Kontra Coffee.
She took out a sample each minut during a 14 minute roast – to show the color change.
George Stavrinou from the Bullet community (he is a Bullet owner in Australia) asked me; what I was trying to achieve with my roast profiles regarding to taste.
To me the most important is:
1) Balanced taste and avoiding bad taste (bitterness, cardbord, burns and so on). A little acidity is okay but not too much.
2) Get big aroma. In light roast I get a certain kind of grand aroma, that I can’t associate with a specific food/flower/whatever. I like deep aromas that stays as a pleasant aftertaste in the mouth for a long time.
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
Taste: 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:
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 ?
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.
I 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.
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.
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
Settings 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.