The old roaster has barely been run-in, and already its undergone a major modification. Original description is here:
Now, *Iíve discarded the store-bought chicken rotisserie motor drive which spins at only 16 RPM Ėand thatís at 6V DC, twice the intended voltage. Too slow for even roasts.
Itís been replaced with an old car window electric winder motor complete with its reduction gearbox. *At 12 V itís blindingly too fast. But 9V gives 56-60 RPM. *It is very, very quiet, too, and thatís important when listening for that elusive crack above the din of motors, hissing natural gas burners and pounding heart. * (I was even contemplating using an old Skil battery drill, with its useful chuck. I gutted it, throwing away the 25-year old rechargeable batteries and using a battery adapter instead. But itís too fast and the reduction gearbox too noisy)
The first, experimental attempt unfortunately offered up too many variables to deal with all at once: when is first crack? Is the oven thermometer sitting on the hot plate adjacent to the middle burner (over which the drum turns) accurately indicative of the temperature in the drum? *In any case, the 3 pieces which make up the rotisserie bar unscrewed halfway through the roast, necessitating opening the lid, losing all the heat, screwing them back together, and then reversing the polarity to counteract the unscrewing effect.
Away we go again. The motor is ultra quiet, but the spinning beans make a hell of a din, and so do the gas burners. I listened for a cracking noise, with much difficulty. It finally happened, and the little smoke and burning smell compelled me to panic and stop the roast. I emptied the beans into a stainless steel colander and blew them with a small personal fan. This has the effect of not only cooling them, but blowing away chaff.
The roast was fairly uneven. Despite that, 24 hours later, I pulled a shot. My Iberital grinder was adjusted to suit some roasted decaff *beans bought yesterday-they are virtually undrinkable, with awful, bitter taste, white crema and thin viscosity. *The first shot of my homeroasted Ethiopian beans did not extract at all because the grind was too fine. *Turned knob back one full turn. A little better, but only about 10 ml in 30 seconds. *Another turn back. AhÖIíve never seen such a beautiful sight emerging from Silviaís portafilter spout. Like honey trickling, thick but slowly. Thirty millimetres of viscous fluid in 25 seconds, almost all dark crema. *If the cup had been a swimming pool you would have floated on top without sinking, which is what the sugar did.
I now have a second batch, which is of a very, very uniform roast, maybe a little on the dark side. My daughters sharp hearing was put to use listening for that first crack. *Will pull a shot tomorrow morning, 24 hours after roasting. But if that first batch is anything to go byÖ..weíre knocking at the door to coffee heaven.
Technical info: BBQ preheated to 210 degrees C. Roasted at 210-220 degrees at 56-60 RPM. First crack at 9.30 mins. Second crack at 11.30 mins. Stopped roast at 12 mins.
Temperature relatively easy to keep consistent. Itís a three-burner, but equivalent output to 6 burners. Keep iron hotplates on left and right burners for critical mass, remove the centre hotplate but leave ceramic bricks over middle burner to even out heat. *Leave middle burner on high, adjust temperature by going low/high on side burners.
Hope this helps
PS: My store keeper cant tell my what type of Ethiopian beans shes sold me. Perhaps someone can help: they are about 10 mm long, *a very pale green.
Progressing well Robusto.
Comment about temperature. Your thermometer may or may not be accurate but it will be fine as long as you understand what temperatures deliver the results you want to achieve.
A roasting "rule" that has served me well is to have your roast finished in the range 12 to 16 minutes. If you achieve timing in this range, your temperature and roast curve must be pretty close to the money. Recently I have started to include a period of about 4 minutes on low heat to dry out moisture and then ramping up the heat to reach first crack in 10 to 12 minutes, cutting back for 3 minutes and then nudging it up again to get to second and to whatever degree of depth I want to finish at. The preheat seems to produce greater consistency, particularly with the Yemen Ismaili which is notoriously difficult to roast to a consistent colour.
Lets know how you go with other beans.