The first stage in roasting. The beans turn from green to a yellowish color. Grassy/earthy aroma present.
The second stage in the roasting process. The beans begin to brown. Just prior to Cinnamon roast. The moisture in the bean begins to vaporize.
At this stage the beans continue to expand, releasing water and gasses trapped inside. This expanding makes a "cracking" noise. Also at this stage, the papery membrane surrounding the beans begins to peel off. This is called the coffee "chaff". At this stage, the beans have a very uneven brown color.
The beans have a medium brown color. They have all expanded, reducing their weight, but nearly doubling their volume. At this point in the roast the varietal character of a bean starts to develop.
Full City Roast
Medium dark brown color with some slight oily drops, beginning of second crack. Varietal character is still intact with a little bitter sweetness. 10 seconds or so into second crack of bean.
Vienna Roast / Second Crack
At this stage the beans turn darker brown and have entered the second crack. During the second crack the beans begin breaking apart due to the weakening of the cellulose structure. You cannot taste as much of the bean's natural flavor. This roast like the roasts following French, Italian, and Spanish are moving quickly along the second crack, will give the smoky/burnt taste undertones in the flavor.