This weekend I finally managed to combine all the various bits for the laptop roaster having finished building the thermocouple amp, so I was able to turn my mind back to the coffee roasting rather than the roaster itself.
It's early days, but so far I'm very pleased. Jim Schulman has posted extensively on alt.coffee about his profiling experiments with a variac and I decided to start by recreating one of his experiments: 3 roasts, the first typical of a popper with a steep rise in temperature at the start, flattening out towards the end, the second starting very gently and ramping up as the roast progresses (more like a hottop) and third an almost straight profile like a commercial roaster.
I tried the 'correct cupping procedure' but it went something like this: yuk... this isn't how i like my coffee, so 3 cups of filtered coffee with milk and sugar later things were tasting much better
More seriously though, the first (popper) profile showed all the deficiencies that lead me to this project in the first place, little scope to create an even light roast, far too much acidity and under developed origin flavour (requiring long rests to improve) as well as bitterness from the prolonged spell at high temps.
The second, concave - hottop roast improved on all counts and although the second and third profiles were very close, in my opinion the straight profile was the best on all counts, no acidic astringency, no bitterness, good origin flavour development and a well rounded, balanced cup.
One of the biggest surprises was how both the straight and hottop profiles allowed for good light roasts. With the popper profile colour seems to develop earlier in the roast but is usually either uneven requiring all roasts to go to a darker brown stage to even the beans out or just too acidic. With the new profiles, colour develops later in the roast (a feature of commercial roasters I've read), is far more even and controlable and I'd say might actually be lighter for the same degree of roast. I did a batch of Costa Rican and cooled them at an almost 'cinamon roast', they were very evenly tanned and without resting produced a smooth but floral cup. I couldn't have produced a roast that looked like this before and if I had I wouldn't have dared tasting it !
The features of the 'virtual roaster' - the software running on the laptop, are that I can do a manually controlled roast with realtime graphing, and also use any profile I created from a previous roast in an 'auto' mode so I can get the roaster to reproduce them without my input. It's also fairly easy to edit the saved profile data if I want to modify some aspect of it such as eliminating (or adding!) a temperature bump. I've attached a screenshot of it in operation doing a 'straightish' profile after a 300ºc preheat before dropping the beans in. The black shows the roast temperature (possibly reading a little high due to the thermocouple placement) while the red shows heater level as a percentage.
Sorry for the long post, I think in all I did around 12 roasts with differently tweaked profiles this weekend as well as reading a doctoral thesis on roasting (http://e-collection.ethbib.ethz.ch/cgi- ... s&nr=13620) so I'm somewhat saturated with data ! not to mention the best coffee I've managed to roast to date.
Chris