I made an earlier post where I was trying to transfer a roast profile I use on my Diedrich IR-1 gas roaster to the Bullet R1; I received a nice PM which was helpful.
One of the most important observations that I make on all of my roasts is to compare the weight of the roasted beans to the input weight of green beans. I find that the weight loss with roasting is typically 16% +/- 1%, and my most typically observed value is -15.5%. Obviously, one can get to a certain percentage weight loss in any number of ways with any duration of roast, so the weight loss is only comparable if one is using a similar profile with similar time-temperature observations.
That having been said, my first two Bullet roasts, both using DP Ethiopians I like for single origin espresso, 1lb of green coffee (454 g) per batch, produced less roasting weight loss than I expect; 14.5% in one case and 15% in the 2nd. The beans look slightly under-roasted to my taste, but it’s too early to try them yet (only roasted last night).
My questions are: (1) Using the bean temp, at what temp do you normally call the onset of 1st crack? And (2), also using bean temp, what is the temperature “delta” between onset 1st crack and the very beginning of 2nd crack for most of your roasts?
On my Diedrich, roasting at altitude, I usually call onset 1st crack as occurring around 375 F; on the Bullet, this seems to happen at a lower temperature, around 355 F (179.4 C) from what I’ve observed. On the Diedrich I have a “delta” between crack onsets of about 44 degrees F (24.4 C). When I used that “delta” to guide my 2 roasts last evening, I ended up with beans that are probably a bit under-roasted.
Do any of you have observations like this, e.g. how many degrees in bean temp do you typically notice as being present between onset 1st and onset of 2nd cracks?
Obviously, you can go up 44 degrees F (24.4 C) in 2 minutes or in 5 minutes, depending on how you control your heat input and your ventilation, so this may be an unanswerable question depending upon what coffees you roast and what you want your coffee result to be, but I thought I would ask.
Thanks for any replies!