Roasting basics

This is basics about roasting coffee. Mainly focused on roasting batch sizes on 0,4-1 kilo.

My name is Therese. I 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.

Just remember; nobody has the ultimate truth about roasting, there are many approaches.

risteparty1sh-aug2016

 

Content
Scope of the roasting process
Preheat temperature
Power
Fan/airflow
Drumspeed
Bean characteristics
Bean temperature (BT) & Turning point
Yellowing
ROR curve
Development time (DT) & Roast degree
Cooling
Weight loss
Scorching and other roasting defects
Fine-tuning the roast profile
Taste is king

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

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Scope of the roasting process

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

The first two things you should focus on when roasting coffee:
1) The heating up process – how quickly the beans are heated up
2) Determine when to stop the roast

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1. Heating up
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 the outer tipping-in-beansof the bean get roasted quicker than the inner – the coffee will taste 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 (taste like old bread).

Too little heat will give a late First Crack – which gives a weaker sound = more difficult to hear.

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 cracking is over, its silent for a while, and then starts a second crack (SC).

To me a late FC is like after 11 minutes. And a very early FC is before 7 minutes. Oppinions differ. You must explore what suits your taste.

When I roast coffee, my aim is to get a First Crack (FC) start around 7-9 minutes but thats for a light roast of high grown beans. For darker roasts and espresso, I go for 10-11 minutes.

A step deeper: instead of the total time from start to FC … you can look only at the time from Yellow point to FC. I know a roaster who focus on this instead of the whole time to FC. He like that phase to be 3 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. Some look at the bean temperature. Others go by the color of the beans or the smell of the roast.

I use the time from FC start and adjust it acording to the bean temperature rise (quicker rise -> shorter time).

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.

preheat-vs-fc-start-500gr

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.

Later on we went on a roasting course and here Michael suggested more heat to begin with. He used preheat 200°C for 700 grams batch.

Notice: the first batch needs more heat because the roaster itself isn’t fully heated.

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.

Power

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

Develop your own strategy for when to change the power setting depending on the bean temperature (BT). For instance; when the BT reach 150 C, then turn down to P5.

There is a general consensus to: Decrease power in the latter part of the roast. When the beans start getting brown, start turning the heat down – in several steps.

See further under Roast Profiles.
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Fan/ airflow

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

We have seen different patterns in what happens to the bean temperature (BT) when increasing Fan.

At 400 grams I have seen the BT increased First when increasing Fan (like applying heat with a hairdryer) but only until F4. From F5 it cooled the roast. This seems to depend on batch size; larger batch sizes takes a higher F-value to start cooling.

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:

cleaning-routine-filter

Update May 2017: Aillio has now released a new bigger chaff filter.

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Drumspeed

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.
drumspeed-setting-and-rpm

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. I always use d8.

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 https://joemarrocco.com/2016/10/24/coffee-roasting-measuring-what-matters/

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.

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

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 to TP typical depends on the batch size – larger batch sizes makes later TP.

The temperature of TP says something about the speed of this initial “push” of the heating up process. So very dependent of the preheat temperature.

tp-temp-fc-start-500gr

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.

Yellowing

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 the outer of the bean is getting roasted quicker than the inner. I don’t know what the limit is. Probably its also dependent of the type of bean. But I dont like it to be less than 3 minutes.

Otherwise the time to Yellow point don’t seems to directly influence the taste – the phase from yellow to first crack is more important: how long it is. And that depends on the speed of your roast = the ROR level.

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 use P2, then graduatly rise to the higher heat level within a minute. Note: here soak has nothing to with adding water.

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).

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

Development time (DT)

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

A lot is happening to the taste from the point of First Crack start. Therefor it’s much more meaningfull to focus on how long the beans was roasted from FC start – than the total roasting time.

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, very 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.

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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. 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 combined with the rise in temperature. 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 after yellowing  and around 5 degrees per minute going into First Crack.

In order to get a low ROR after First Crack onset – you need to turn the heat down a while before. With bigger batches, like 900 grams, Steffen turns the heat down to P1 1,5 minute before FC start – or else ROR will rise to much after FC start.

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 http://scottrao.com/blog/development-time-ratio/

I don’t use this rule. I have great tasting coffees at 10% DTR.

See graphs and read about working on the ROR curve in http://coffeenavigated.net/roasting-coffee/graphs/

Cooling

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%.
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tipping-in-beansScorching and tipping

These are roasting defects caused by too much heat.

 

 

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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:
http://genioroasters.co.za/project/tipping-or-scorching-wtf/
http://www.coffeeshrub.com/shrub/glossary/term/650
https://coffeecourses.com/coffee-roasting-mistakes-photos/

and see pictures http://www.home-barista.com/home-roasting/coffee-roasting-defects-pictorial-t13587.html

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 type of 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 http://coffeenavigated.net/roasting-coffee/graphs/

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.

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

 

 

Discuss your roasting with the Bullet

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