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Tuesday, 27 August 2013

Coffee Roasting Notes on Turning Point in a roast

Examining our own preconceived ideas on roasting?

We at Quaffee are forever testing our own roasting knowledge boundaries, we love roasting coffee and love looking at ways to improve and or understand how we can improve our roasts. With the change in temperature and weather recently we have been looking at charge and turn around temperature of a each of our roasts.

The charge temperature (or starting temperature) is the temperature you want the air in the roaster to be when you drop the coffee into the roaster (at that point the coffee is at room temperature). At the point that the coffee is introduced to the roaster the air temperature in the roaster drops and equalizes with the temperature of the beans. When it has equalized the temperature again starts increasing. This point this happens is called the delta point or turning point of the roast.

And so the games begin

So we started play with these turning and charging temperatures trying to see what the results were. What we found was that it affected the way you kick started and controlled the roast from there, but we were looking for a point at which the coffee may change in taste.

So off we went to do some research to see what others had found and discovered that there has been quite a lot of debate regarding this issue however there are also some commonalities:
  • Charge and turning point are roaster specific
  • Flame level at drop is coffee and roaster specific
That said there seems to be an agreement that most important consideration is what happens after chemical change starts. This is when the beans change from green to yellow and then onto brown. roasting profiles linked at yellow browning
Roasting Profiles linked at Yellow Browing

Summary

What tends to be the agreement is that if you roasted the coffee so that the roast profile from the yellowing stage is more or less the same, than no matter what the charge temperature is and the turnaround temperature is it is difficult to distinguish the difference when the coffee is tasted afterwards. A sample of the graph showing these differences is above.

The forum post that I found worthwhile is: http://forums.roastersguild.org/viewtopic.php?f=5&t=87

You can a summary of this discussion on youtube, where we got the original image:

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