City Roast Level (light):
This is the earliest palatable stage that the roast can be stopped and result in good tasting coffee. City roast occurs between 415-425 degrees Fahrenheit. At this roast level the origin flavor isn’t eclipsed by roast flavors, but the risk is that sourness, astringency, or under-developed sweetness can make the cup unpleasant. City roast generally has a light brown color with strong surface texture, even dark creases in the bean surface, and only moderate expansion of bean size. This varies greatly in different coffees, though.
City+ Roast Level (light medium):
This roast level occurs roughly between 425-435 degrees Fahrenheit. The coffee has been allowed to develop anywhere from 10 seconds to 1 minute or more, depending on roast method, after the last “pop” of First Crack. At this level, there is a balance between moderate roast flavor and the origin flavor of the bean. Astringent, sour or “baked” light roast flavors are reduced, yet the flavors specific to a particular coffee lot are still expressed in the cup. City+ roasts have a medium brown color and may not yet have the smooth surface that with further development towards Second Crack.
Full City Roast Level (medium):
Full City is right at the brink of Second Crack, roughly between 435-445 degrees Fahrenheit. At this roast level, certain qualities of the bean's origin might be best experienced when the roast flavors are actually greater. Many Sumatra coffees fall in to this category. Full City roasts have a much more uniform dark brown color and have a smooth surface from the browning and bean expansion that occurs as the coffee is on the brink of Second Crack.
Full City+ Roast Level (medium dark):
A coffee that’s been roasted just up to the first few snaps of second crack are heard and then terminated, roughly around 445-450 degrees Fahrenheit. At this level roast flavors begin to dominate, which tones down certain origin characteristics and creates a harmony between the two. This is an ideal roast level for single origin espresso.
Vienna Roast Level (dark):
Vienna Roast occurs at the beginning of second crack, roughly around 450-460 degrees Fahrenheit. The Vienna stage (also called Continental) to Light French stage is where you begin to find origin character eclipsed by roast character. If you buy coffee for its distinct origin qualities, heavy roasting is at odds with revealing those nuances. Nonetheless, some coffees are excellent at this stage. Vienna is a common roast level for espresso.
French Roast (very dark):
Sugars are heavily caramelized (burned) and degraded. This occurs roughly around 460-470 degrees Fahrenheit. At this stage, the woody bean structure is carbonizing, the seed continues to expand and lose mass, the body of the resulting cup will be thinner and lighter as the aromatic compounds, oils, and soluble solids are being burned out of the coffee.