Looking at our own preconceived ideas on roasting?
We at Quaffee are like testing our knowledge and roasting know how, 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 the last few month we have been looking at charge and turn around temperature of a roast.
The charge temperature (or starting temperature) is the desired temperature you want the air in the roaster to be, when you introduce the green coffee into the roaster (the coffee is obviously at room temperature). At this point the air temperature in the roaster starts to drops and eventual equalise with the temperature of the beans. When it has equalised the temperature again starts increasing, this is the that 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 to try and see if they would affect the final product. What we found was that these temperatures where important in how they affected the way you kick started and controlled the roast, however we were looking for a point at which the coffee may change in taste.
Finding little difference in taste we were a little perplexed so we did 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 to the coffee after chemical change starts. Chemical change is when the beans change from green to yellow and then onto brown.
Roasting Profiles linked at Yellow Browing
From our experience and reading many roasting forums and the video below we can conclude that if you roast 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.
You can also view a summary of this on youtube:
[youtube=http://www.youtube.com/watch?v=hS0SfzypyFQ&w=560&h=315] where we got the original image.
You can also read this forum post: http://forums.roastersguild.org/viewtopic.php?f=5&t=87