Hi gang,

I have a modified popcorn machine. I am feeling to get better result when I slow down the first phase of heating (before first crack), and then accelerate the second phase. But I am not really sure. All this by controlling the speed of the air blown. The thing is that I am using so much beans making tests... it is starting to take a lot of my money and my time. So I am wondering if some of you know if there is a perfect shape of curve to have. When I do not control the temperature, the curve looks logarithmic (on a linear scale of temperature and time). And what I tend to do is to make it look more linear.

I also have troubles with temperature. Maybe my thermometer is not well calibrated. But it is one of these precise numerical thermometer, so I do not think so. On the Internet, people usually claim to have the first pop around 400F, I get it at 430F or more, and I can keep the temperature under for a long time, it will never pop. Even worse, if I wait too long, then there is not first pop anymore when I let it pass 430F. And the second pop, it starts at 460F, and get really into it at 470F. And this with any bean I tried.

On measuring: You may be measuring too close to the bottom of the roaster, where the hot air is entering. For air roasting, measure the temperature at the top, as the air exits. Here the air has exchanged most of its heat with the beans and the temperature will be close to that of the beans.

On the Roast Profile (that's the term for the bean's temperature versus time curve): You can divide the roast in three, the drying phase up to 290F or 145C. Spend about 3 to 5 minutes getting to this point, so the beans have reached a yellow color. Up to 400F or 205F, the first crack, where one gets Maillard reactions but no caramelization: take this part of the roast as fast as possible unless you want to develop woody and malty flavors, around 3 to 4 minutes. The final phase, go faster for brewed coffee, slower for espresso, three to five minutes.

Good luck.

Oh thank you very much for your very precise answer. I will try this tomorrow.