Finding and setting your perfect curve & parameters with Norwegian Coffee Roasting Champion Simo Christidi

1) Roasting Curve File: Roast Profiles

Simo C: Whenever a new batch of green beans arrives, in order to find the best (or right) production profile, our standard approach is to have three different profile roasts first, and compare the three different profiles of the coffee. Having a powerful tool as Cropster, gives us the possibility to investigate all our previous profile database. Based on this  and adding the technical information of the coffee (such as humidity, bean size, etc), and the sensoric expectations, all those factors will help us to find the right direction while profile roasting.

We know from QC cuppings that across the three different roasting methods, even with a different roasting end time of up to 90 seconds, you still clearly retain the characteristics of Kenyan beans, such as red currant, berries and floral notes. The difference lies in the intensity of sweetness, fruity notes, and acidity, which will vary with the length of the Maillard reaction.

Figure 1 shows a Kenyan coffee and the three profile roasting attempts.

*  Blue curve: Intense acidity, floral notes
* Yellow curve: More sweet, body and mouthfeel
* Red curve: Balanced between sweetness and acidity

For people unfamiliar with profile presentation in Cropster (and it’s built in roast compare reports), each of the blue, red, and yellow curves represents the bean temperature curve and the RoR (heating rate) curve for the three roasts. The place marked by the small circle corresponds to different roasting events. The left side is the “turning point” and the right side is “first crack”. The three beans of the three curves have the same temperature and the same development time.

As for how to select the best (or right) curve and determine the length of the roasting time, it depends on the origin of the raw beans and the physical characteristics of the green coffee. For me, the historical roasting data Cropster stores always leads me to make the right decision.

2) Roasting target: Roasting Goals

The roaster’s job is to create a roast profile which will allow coffee to develop in a way that will give you the best taste.

For me, the most important roasting parameters are “drop temperature” and “batch size”, and the two interact with each other and need to be clarified before starting roasting. In addition, since the gas setting at the beginning of roasting is also dependent on the “amount of roasting”, in order to ensure the target roasting duration, the temperature of the beans is crucial. Here are some key values I use for my roasting, for your reference:

Lower bean temperature range

  • 200 ° C: when the full load rate of the roaster is between 50% and 100%
  • 170 ° C: when the full load rate of the roaster is less than 50%

Roasting duration

  • Filter coffee: 8-12 minutes
  • Espresso: 10-13 minutes

Development Time Ratio (DTR)

  • Filter coffee: the ideal development time ratio is 10-14%
  • Espresso: The ideal development time ratio is 18-22%

Other roasting values and tools that will be measured and recorded:

  • Development level of the roasted coffee (color measured with Colorette, Colortrack or Lighttells, etc)
  • End temperature (with Cropster)
  • Development time and Development Time Ratio: for professionals those 2 elements are key factors for the roasting process (with Cropster)
  • Total roasting time (with Cropster)
  • Cupping score (with Cropster)

3) Heating rate curve and RoR peak

It’s essential for every roaster to try different profiles and taste the coffee in order to determine the curve. The RoR curves vary depending on the roasting machine, the batch size and the positioning of the probe. The following values are a summary of my personal experience and are for reference only:

  1. 1) The peak RoR usually appears within the first 3 minutes of the roasting process.
  2. 2) The peak RoR will affect the total roasting time, but also depends on the type of coffee, freshness and density of the green beans.
  3. 3) The peak RoR of the bean temperature is also affected by other environmental factors, such as ambient temperature and moisture.
  4. 4) RoR interval of 60 seconds works fine for me.

Blue curve : In order to maximize acidity and floral notes, the bean temperature RoR curve is very high with a peak of 38 ° C / 60 seconds.
Yellow curve : In order to extend the roasting time and seeking for body, sweetness and complexity, the peak RoR is relatively low.
Both curves have the same values for: drop temperature, turning point, and development time.

My rules for a good roast and reliable curve are as follows:
1) My curve will always be gently descending
2) My curve will have a certain RoR when it’s starting to crack
3) My curve will have a certain RoR when the roast is finished

Please Note: The RoR curves will vary from roaster to roaster. The above curves are taken from a Loring Kestrel S35 and 20 kg batch size.

My advices to my fellow roasters!

  • Start with buying good quality of green beans! Bad beans will never taste good no matter how you roast them.
  • Take some time to find a good roasting machine. There are many good ones out there!
  • Record your roasts! Cropster has always been and will be my favorite logging system, and I have used it every day for the past 6 years.
  • There are many factors affecting your roast, approach them one at a time. Don’t get confused! Get notes and study your roast profiles.
  • Taste your coffee daily and do blind cuppings! Do comparative cuppings to update your profiles.
  • Keep learning and stay updated with the latest news in the specialty coffee industry.
  • Share your passion!


One reply on “Finding and setting your perfect curve & parameters with Norwegian Coffee Roasting Champion Simo Christidi”

hi… i’m Sam i work in Muscat Oman , I would love to ask you how to calibrate a coffee roasting machine and how to reduce and increase gas and airflow to get perfect profile curve

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