Roasting basics

This is basics about roasting in general.

I started this because in the summer of 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 (Therese talking). But of cause, much of it can be used on other roasters too.

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)
Cooling
Weight loss
Scorching
Fine-tuning the roast profile
Taste is king

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

beans-smoke-sh2

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) Even development of the bean,
2) Determine when to stop the roast

When you got hold of this, you can move on to fine-tuning the roast profile. Just know that you can not make a coffee taste good by only using fine-tuning (like make a nice shape of the ROR curve), read more below.

 

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 … instead of a nice full development.

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.

My aim is to get a First Crack (FC) start around 8-9 minutes but thats for a light roast. Medium or dark roast I find 10-11 minutes best.

 

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

Set the preheat temperature according to batchsize (grams) and depending on when you want to reach First Crack (FC). I prefer a FC start around 8-9 minutes (Therese speaking) for light roasts. I know others who are content at 11 minutes. Recently, I have discovered that 10-11 minutes is better for medium/darker roasts/espresso.

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.

preheat-vs-fc-start-500gr

12 batches, all 500 grams – roasted by Steffen, starting on P8 and the 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
The preheat time should be at least 20 minutes (or just wait until the Bullet says “Charge”).

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 195 and P9.

But room temperature also makes a difference.

More data is needed 🙂

Power

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.

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

See further under Roast Profiles.
.

beans-trier-sh1

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:

cleaning-routine-filter

.

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.

Davin from Canada got an earlier FC at higher drumpspeed. He writes
“I charge 800g of beans, P9, P2/P3, D7 where the TP is at 1:00. Yellowing starts at around 4:10, and I begin dropping power at 5:00 and continue dropped power every 1 minute past that. First crack is at 8:28.
When using these same variables and only increasing the drum speed to D8, nothing changes with the ROR but FC starts earlier at 8:13 and therefore the roast is stopped quicker to reach the desired 25% development time. I thought this was interesting and I preferred the taste of the profile using the D8 speed over the D7.”

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 measurements cannot be compared from roaster to roaster. You cannot use that FC starts at 200°C in one roaster. It can be 180° or 207°C in another roaster. You just have to get to know your own roaster.

Bean temperature: Turning point

Turning point is when the Bean temperature (BT) turns around after 1 minute of roasting. The initial drop in BT is a mix of temperature in the bean probe before adding the beans and the temperature of the beans (room temp).

Make notes of the lowest temperature for TP and how it correlates with time for FC. This can be useful to indicate is you are going to arrive at an appropriate FC time – or you need to give adjust the heat during the roast.

tp-temp-fc-start-500gr

This graph is 12 batches, all 500 grams, roasted by Steffen. 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, 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.

 

ROR curve

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

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

But avoid the ROR going beyond zero – and avoid ROR dramatically rising in the last part of the roast (the initial big rise within the first minutes is suppose to be like that).

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 after FC.

Much discussed are the theories of Scott Rao on always 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/

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

 

Development time (DT)

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

How to determine FC start

Light roast has DT from 50 seconds to 1:50 minute
Medium roast around 3 minutes
Very dark could be at 6 minutes
– Thats just to give an idea. There is no common difinition of this.

 

 

roaster-door-dump-sh2

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.

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 or color of the bean.

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.

 

Cooling

When you stop the roast fast cooling is necessary.

Aim: Get below 40°C in 4 minutes.

Weight loss

Weigh your roast before and after roasting. The weight loss in percentage 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.

 

fil-01-12-2016-10-59-58

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 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.

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.

la-cabra-2sh

 

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

 

 

Discuss your roasting with the Bullet

The unofficial Bullet forum

Groups on Facebook like https://www.facebook.com/groups/1667530986833160/