After approximately three to four minutes (some claim it's 6-9 minutes), the beans will enter a stage called first crack (a small snapping sound emitted from the bean as it increases in temperature). This depends on what method (or roaster) you use. Let the beans completely finish the first crack stage, this is what is considered a light or city roast. It's also called the New England Roast. The second crack is when you have hit the dark roast stage...This is called the Full City Roast.
Let the roasted beans stand for at least four hours before grinding, this lets the Co2 gas off.
All methods of roasting produces chaff and smoke, especialy in the darker roasts. Don't worry about this but instead take measures to control these two by-products. Kitchen fans work great for the smoke, or you can roast beside a window or outside. Very cold temperatures can affect the ability of the roasters to achieve the proper temp. Chaff can also be contained with a bit of planning. Manufactured roasters have chaff collecting features built in. If you use one of the above mentioned methods, roasting outside or in the garage may be the best solution.
I have found that the Hearthware is very sensitive to changes in the WEIGHT of the green coffee you use in a batch. You must weigh (or use their included measuring cup) the coffee, and be consistent!
Links to Roasters Alpenroast and Hearthware are two leading manufacturers.
In a nutshell, here is the roasting process you will be observing, using the Alpenrost:
For the first 5 minutes the bean remains greenish, then turn lighter and emit a grassy smell.
The beans start to steam as their internal water content dissipates.
The steam becomes fragrant. At around 15 minutes on the Alpenrost you will hear the "first crack," an audible cracking sound as the real roasting starts to occur: sugars begin to carmelize, bound-up water escapes, the structure of the bean breaks down and oils migrate from their little pockets outward.
After the first crack, the roast can be considered complete any time according to your taste. The cracking is an audible cue, and, along with sight and smell, tells you what stage the roast is at.
Carmelization continues, oils migrate, and the bean expands in size as the roast becomes dark.
At this point a "second crack" can be heard, often more volitile than the first. Small pieces of the bean are sometimes blown away like shrapnel! It can be more difficult to hear than the first crack though. This happens around 19 minutes on my Alpenrost. The cooling cycle begins when you hear the sound of the Alp. vent doors click open.
As the roast becomes very dark, the smoke is more pungent (oils burn against the hot surfaces of the roast chamber) as sugars burn completly, and the bean structure breaks down more and more.
Eventually, the sugars burn completely, and the roast will only result in thin-bodied cup of "charcoal water."
