Home Roasting

Beans are dark but the brewed coffee tastes bitter and weak.
This occurs because coffee is under roasted. The second popping never took place. It is better to over roast coffee than under roast it.
Popping doesn't occur after 10 minutes of roasting. (Popcorn or Melita roaster)
Your temperature is too low. Use more beans next time (don't add more this time) to keep more heat in the roaster. Or, cover the opening of the popcorn popper until the first pop is well under way. Placing your popper in a shallow bucket or box will increase the temperature of the roaster. Do not place a lid on the bucket because damage may occur to your roaster.
Beans aren't evenly roasted.
Typically, this is because the beans are not sufficiently stirred throughout the roasting process. Perhaps you're using too many beans, and the forced air is not strong enough to properly stir them. Or perhaps you need to stir them at the beginning of the roasting process when they may be too heavy to be adequately circulated by the air.
My beans aren't oily.
When the second popping is under way, oil patches will begin to appear. If you do not hear any popping, the temperature is too low. You must increase the temperature until popping occurs.
Some beans take longer to roast.
Coffees grown at high altitudes are dense and take longer to roast. Humid weather will also affect the roasting time needed to roast beans due to the amount of moisture in the air. In either case, you can raise the temperature. This will speed up the roasting process.

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