What I wanted to say...

Before Blogger shit-canned my work for the 3rd time, what I wanted to post about is my issue surrounding the runaway loss of heat at the end of the roast. I didn't have to deal with it when I started with the Bullet back in Jan 2019, but it's a familiar quirk these days.

I whined to an internet acquaintance about it and Stuart's feedback was phrased in just the right way to make me see what I've changed that needs to be unchanged. He said:

As you note, one of the perils of the Bullet with it lacking any significant thermal mass is once you drop off the cliff with thermal momentum, you’re kind of screwed.

I had whined that I was already at P9 (the highest power setting on the Bullet) and 'there's nothing left in the tank to get heat into the drum'. This has been happening at the end of the roast as 1C starts. Rate of Rise (RoR; the 1st derivative of Bean Temp) measures how fast temperature in rising in Fahrenheit degrees per minute (F°/min). As long as the curve is visible on the graph, Bean Temp is rising. But the shape of the curve tells me whether Bean Temp is going up in a linear progression or if it's accelerating or decelerating; conversely, if Bean Temp is going down I'll know that because the RoR curve will disappear.

The plan is to get to 1C then keep RoR steadily declining to a target of about RoR = 10F°/min just as the beans reach their target temp at the end of the roast. So it's a juggling act of sorts.

I looked back at some of those early roasts and concluded I did a terrible job meeting the criteria I'd set for myself. Yet we still had some decent coffee (or maybe the Admiral is just a patient person who hoped I would eventually get it right!).

Whatever the case, I found nothing in the old roasts sufficiently outstanding to point at. I did see Preheat temp setting migrated from 360°F -> 392°F -> 401°F -> 410°F -> 428°F -> 

Early roast that stalled. RoR looked good but the coffee was crap.

 

Looking at the charts and paying attention to RoR at the end of the roast I appear to have had better RoR management at 428°F Preheat than I did at lower preheat temps. That was disappointing to see as I have tried to follow (in a general way) the profile that I got from Julio Nungaray. In that profile I start at 392°F and steadily increase power. In the better managed roasts I did about 4 months into using the Bullet I used steadily declining power and had some semblance of control at the end of the roast. Hmmm.

Furthermore, I noticed I did a less than stellar job of marking 1C on the chart. And I had 2C starting at impossibly low temps. Apparently I did a piss poor job picking out the sounds in those early days. Things didn't get better till I discovered the article pub'ed by Thompson Owen where he recorded temp data along with color, aroma and sound notations. 

 

There is the possibility that the IR data (Drum Temp) varies as a function of Preheat. I did notice the difference between Bean Temp and Drum Temp is greater at higher Preheat temps. I'm inclined to think Bean Temp won't have that variability, but I can't be sure till I review the more recent roasts where I believe I do a better job picking out the sound of the crack.

This is getting long so I'll pick it up again in the next post.