The art and science of Specialty Coffee Roasting

The art and science of Specialty Coffee Roasting

Today’s topic of discussion is The art and science of Coffee Roasting.

Before we begin, I thought of sharing some news floating around specialty coffee. A somewhat different start to our podcast today than usual.  

Here you go!

India’s coffee exports have increased by 12% in 2021. The growth is largely attributed to robusta production, which accounts for 70% of the country’s exports. The Coffee Board of India announced its intention to export US $1 billion coffee this year.

As discussed before robusta, unlike arabica, grows well in even adverse climatic conditions. Though inferior to arabica, in terms of taste and quality, robusta is consumed on a large scale in some countries including ours. 

It is usually added to espresso based coffees to add body to the whole cup and enhance the eye catching crema ! 

But yes robusta is being treated differently nowadays and there are some natural and honey processed robusta out there as well. 

Up on the newsfront the second one is about a documentary. 

It’s Bean Too Hot documentary focuses on the effects of climate change on smallholder farmers. The 30-minute documentary focuses on climate-neutral coffee farms and sustainable farming practices. Czech filmmaker Hedvika Michnová will premiere the documentary on 7 September via YouTube. 


Jägermeister opens first coffee shop. It is located in Shoreditch and serves Caravan Coffee Roasters. Next to the café is a Jägermeister Cold Brew coffee dispensing billboard where customers can fill bags of roasted beans.

Thanks to for this updated and insightful data.


Back to our topic of discussion. 

So today we talk about the roasters. Where we come in, what role we play in the whole cherry to cup journey and more deep dives into:

  1. What exactly is a roaster?
  2. What's a roastery like ?
  3. What's the outcome of a roast?
  4. How roasters are responsible for flavour profiles that we all enjoy in our cup
  5. And more !

So in a nutshell, roasting is not just a process of turning green beans to brown roasted ones. But a journey of about 20 minutes, which is far more complex. Let me explain. 

Let's go one step at a time.

First, The roastery: 

I would like to take as an example to help you understand better. 

So, a roastery is a workplace where the green coffee beans are stored in ideal temperature conditions to preserve moisture content, the cupping lab where tasting notes and profiles are determined, the tasting lab where coffee is brewed, the packaging and dispatch station for deliveries. 

A total of 1500 sq. feet of place is what Grey soul coffee roastery resides in.  

Second comes the Roaster and his team, 


The day-to-day responsibilities of a head roaster are aplenty. 

“To start the day, theroaster will turn the roasters on, and then start to schedule batches to be roasted based on sales.

“After that, we will move to the cupping lab and cup the previous day’s roasts. Based on that the adjustments to the roast will be made in order to be consistent. These changes will be recorded in the software connected to the roaster. 

Once these initial adjustments and roasting is complete, a roaster will end up overseeing the packaging process to ensure the packing team gets the right batches.

So this is it, a day in the life of a roaster.

Third comes, the roasting process

In theory, roasting involves a roaster feeding green beans to roast coffee so that it eventually becomes brown in color and develops those amazing flavour profiles and aroma.

Btw if you are wondering what green beans are and are new to this podcast then I recommend you listen to the 1st episode where we explain cherry to bean and bean to cup journeys. 

So roasting is basically manipulating taste profiles of different kinds of coffee and differently processed ones too. 

It is a skill and an Art that requires a roaster to :  

  1. Pay thorough attention
  2. Understand Graphs 
  3. On occasions write some code to make software adjustments  
  4. Understand air flow 
  5. Understand heat temperature
  6. Understand Drum speed
  7. Knowing when to charge and when to drop 
  8. Understanding roast levels 
  9. Understanding of flavour profile creation
  10. And more ... 

But, there are countless more steps involved in between that require skill, knowledge and focus to perfect a roast. 

And thus today's episode is called the art and science of coffee. 

As the whole process is an art and there is a lot of complex and intricate science involved. 

So what are these steps and what are the fundamentals? 

The green bean once loaded goes through the following stages: 

  • Charge 
  • Turning point 
  • Dry end 
  • FC start
  • FC ends 
  • SC starts
  • SC ends 
  • DROP 

But before that, let's understand the roaster itself. 

The giant all metal piece of machinery without which none of us today would have a delicious cup of specialty coffee. 


It comprises of several parts like: 

  • the roast chamber inside which lies the drum in which coffee roasts and gets evenly roasted
  • The chaff collector when leftover and burnt out coffee resides
  • The exhaust that helps smoke out of the machine 
  • The fan and cooling tray that prevents further development in coffee post roast is complete 
  • Of course the burner connected to LPG cylinders which provides the needed heat to the drum

It comes in various sizes and brands. 

Starting at as low as a 5kg one to all the way upto 120 kg and beyond. 


Btw the roaster can be controlled remotely using your mobile phone, through the touch panel mounted on the machine and through a laptop. 

So once connected, the beans are loaded into the roaster.


Back to the stages.  

As heat progresses , The first stage to highlight is the turning point. 

Basically lets say you drop the beans inside to roast inside a already hot machine at 150 degrees. 

So beans that are not at that temperature will bring down the temperature to about 90 for a minute or a minute and a half and then stop. 

Then begin to rise again. 

So this becomes the turning point. 


Second stage is the dry end phase. 

So basically beans go from green to yellow to light brown to dark and all the way till the darkest brown until charred. 


So once you see the beans turning from green to yellow. It's called the dry end phase. 

Dry end because the moisture in beans drops significantly which usually is at 11% (but then again why 11% and what it drops too is a topic for another day and perhaps the second season) 


Third phase is the most crucial.

Its fc start

At this stage the beans are now Completely brown and start cracking. 

Basically if you have some beans around then look close, you will find a crack exactly down the middle of the bean thats a crack developed during roasting when beans release the trapped gases and the roastery is filled with sensational aroma. 


Anyways back to fc start. 

This is where a roaster pays more attention and uses his skill and tries to control various parameters to develop the bean slowly going forward to develop optimum flavour profile. 


Then comes fc end, basically cracking noise stops here. No more popcorn popping sound until the bean reaches a second crack. 

Yes indeed it cracks more and keeps cracking until sc end and even beyond.

So usually espresso, cold brew, french and vienna roasts go up to this level again depending on the roaster preference and flavour profile. 


Eventually comes the drop. 

As the name suggests, you end up dropping your roasted fresh coffee onto the cooling system to try to cool and stop further development. 


In the end, cooling takes place for about 10 minutes and this concludes a successful 20 minute roasting process.

But as mentioned there are too many intricacies involved which we won't get into today. 


But one topic that we will get into would be DTR. 

Why because it helps you as the coffee community and patrons make informed decisions before buying based on it.


DTR is basically Knowing when to stop. 

Stands for development time ratio. 

Ranges from 0-25% 

Basically the time after the fc starts . 

And how long you allow it to be inside the drum until you drop it. 

The longer the dtr the better the coffee. But again not that simple. 

A dtr of 10% might work wonders for some beans and even 20% might work better for some. 

So technically dtr is directly dependent on the kind of bean or the coffee processing it went through. In a nutshell anything above 10% should taste better and anything lower can lack flavour. But again just achieving 10% and not roasting the coffee enough will not result in an ideal flavour profile. 

Usually specialty coffee is dropped somewhere between 203 to 214 Degree Celicius.  


Also as mentioned before, coffee processing is also a crucial step that ties it all together. To understand it better go checkout episode no. 2. We at Greysoul Coffee are involved neck deep into processing to deliver unique flavour profiles to you all. 


Let me share a quick roast story of my own. 

So when I first started roasting, I had a similar style. 

But then I came to realize that roasting in a particular fashion with a plus or minus of 10 degrees may not help. 


For eg: During my training days, I used to charge my coffee in the range of 60 - 75 degrees. 

And roast as per the coffee process and usually roast them medium. 


So basically charge at 60, FC at 194 and drop at around 204 degrees.

But soon realised that it's not the case for all and especially for naturals and experimental processes. So when you roast naturals so must charge the beans at about 50-55 degrees which will help you control the roast beyond FC and achieve a DTR of 15% 

When roasting naturals, due to their higher sugar content they tend to roast faster and it's easy to lose control over your roasts and drop early or late. 


So another approach can be like this, 

Charge: 200c, with burner at 20%

Gas 80% @ 1:00

Gas 60% @ bean temp (bt) 150

Gas 50 @ 160

Gas 40 @ 170

Gas 30 @ 178

Gas 20 @ bt 184

Gas 10@ 10% DTR (based on marking FC when you hear 3-4 pops)

Gas 5@ 12% DTR

Gas 1@ 15% DTR

Gas 0 if the ROR looks like it wants to go up.


Another approach, but one that requires focus and quick reflexes to achieve a desirable outcome. 

Any ways not to get too technical but that was just my experience before I eventually got my diploma in roasting. 


So today after having a diploma in roasting and having an experience of so many roasts these things are becoming more apparent, but the learning curve never stops. 

As a matter of fact it should never, because there is so much more to understand and so many different coffee’s out there that no one particular roasting technique will suffice. 

There are more points to note that include:

  1. RoR 
  2. Variable air flow
  3. Variable drum speed


But we aint going to dig deeper into those topics. 


In conclusion, every coffee is different and Requires different roast.

And every different must be brewed separately. 

For example, a washed medium dark roast would be great for inverted aeropress, espresso and moka pot. 

On the other hand a natural which is medium roasted would not be tasting great as an espresso when compared to a filter. 


Lighter the roast the better it is as a filter and darker the roast it is better as an espresso or even a cold brew. Because the darker the coffee the more oil it releases and this oil eventually under the pressure created by the espresso machine turns into crema. 

Also there is something called the omni roast which roasters try to achieve which simply means a roast that is suitable for all brew methods ! 


So even after understanding its origin, its varietal, the processing, a roaster would still require roasting done at different levels with countless permutations of roast and cuppings to determine the perfect cup. 


And hence, called the art and science of coffee roasting.


When speaking about blends it becomes even more time consuming and requires patience and sensory skills at its peak.


For eg. the mango in loop blend by

Is a culmination of 2 different coffees.

Which means different varieties, different processing methods and may or may not be the same region.


Both will require roasting to be done in several different days. 

Then cupping them individually for optimum flavour profile.

Then cupping them together with different coffee ratios to eventually arrive to a conclusion of best tasting and well balanced blend ! 

Anyways, more about this topic in our next episode ! 


Last but not the least,

Would also like to talk about Fresh roasted coffee.

Apparently it is said that, Fresh means better and the fresher the coffee the better it is. 


Also a marketing term used extensively. 

A term that is given more importance than anything else when it comes to specialty coffee. 


So is it true ?


I believe that a skilled roaster who is experienced in roasting coffees from different regions, of different processing methods and types is not that concerned with freshness, as the end consumer. He is concerned with roasting a particular coffee in a way that brings out the flavours, aroma and complexity leading to a delicious cup when brewed. 

Trust me, it is a process that involves countless roasts, varied cuppings and patient sensory evaluation to reach the optimum result. 

So it's not just the freshness or when it was roasted, but a lot more!


Let me explain. 


When coffee is being roasted it releases carbon dioxide.

Exactly why you see bubbles on your coffee when brewing coffee. 

It continues to do so for a long time. This is also called degassing and thus coffee bags have those valves on them which is essential for large bags of coffee.


Roasted coffee needs to rest. It not only needs to cool down by resting for days before the flavour and the aroma inside is fully developed. 

A minimum resting period is 2-3 days for any coffee before brewing. 

The ideal brewing time would be anytime after 5 days.

But also the ideal and best tasting brew would be in the second and third week since roast. 

But then again even fresh roasted coffee will last and taste better for as long as 45 days. 


When marketed as freshly roasted coffee, the other qualities of the coffee are lost ! 

The process, the varietal, the origin, the roasting technique ! 

So next time you buy, keep an eye on the other elements as well. 


As coffee lovers, coffee enthusiasts and for all of us who drink coffee on a daily basis we should probably focus more on the varietal, the region, the producer, the process, the roast approach and technique, rather than the marketing terms that we all are attracted to. 


In conclusion, yes fresh roasted coffee matters, but it's not about roasting today and brewing tomorrow or a week later. It is going to taste great, good and better as coffee progresses. But that is not what we coffee enthusiasts should consider when it comes to buying your favorite bag of coffee.
So rather, locate the region you prefer more, find the ideal roast for you, see what varietal suits you more and understand coffee processing before buying. 


On a side note, green coffee stays good for as long as 3 years. 

And great for a period of 2 years. 

Again a topic of discussion related to a new crop vs old. 

There is something called the cup of excellence, a global competition that takes place every year. 

To know more about how it is judged and what factors lead to a coffee scoring over 90 do find out for yourself. 


But a topic for another day. 

So, this brings us to the end of todays’ episode. 

Hope you are taking away a lot of information with you like always ! 


That will be all until we perceive each other again ! 

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