Degree of Roast, Temperature, Description
We have high grown coffee with a considerable amount of chaff clinging to the coffee which only indicates that this coffee was not polished (an unnecessary, silly practice anyway). This coffee should give you a good, general idea of roast appearance but every coffee type is different! Dry-processed coffees are not sorted in the wet-mill process, it is done entirely by hand, visually. So the coffee roasts more uneven from seed to seed. Even color is NOT and indicator of roast quality, or coffee quality!
200-250 degrees f. internal bean temperature
At the yellow stage the coffee has a wet-hay or humid grassy smell as moisture begins to be liberated from the coffee and often you will see steam (not smoke) rising from the roaster. Some coffees become quite orange at this time, while others are tan. Sumatras have a unique aroma early in the roast, and earthy-grassy smell.
Light Brown Stage:
250-300 degrees f. internal bean temperature
At this time the coffee has a toasted grain or baked bread smell. Up until first crack the coffee is undergoing an endothermic reaction, taking on heat, but as it undergoes first crack the reaction becomes exothermic, releasing heat/energy.
First Crack Begins:
355 degrees f. internal bean temperature, 395-405 f by thermo-probe
As first crack begins the coffee still appears mottled and uneven in color, as the coffee first starts its expansion in size that is marked by the cracking of the seed. Moisture is being liberated from the interior of the coffee and as it expands the crease in the seed usually opens enough to allow much of the remaining chaff to be released. Since first crack is an exothermic reaction, the beans are giving off heat in first crack, but the quickly become endothermic, meaning that a roaster that is not adding enough heat to the process will stall the roast at this point ...not a good thing. Once caramelization begins (340-400 degrees) a roast that looses heat will taste "baked", perhaps due to the disruption on long-chain polymerization. The melting point of sucrose is 370 f and corresponds to this window of temperatures when caramelization begins.
City Roast, City+ Roast*:
400 - 415 degrees f. internal bean temperature, 425-435 f by thermo-probe
The coffee has completed the First Crack, and has been allowed to brown up a little, but Second Crack has not sounded yet. Not the slightly rough texture the coffee surface, and how it is crazed with darker lines. At this point the coffee has expanded due to the outgassing of First Crack, marking the point where water and carbon dioxide go their separate ways.
In terms of cup qualities, at this stage and the light Full City below you will have the best chance to sense the Origin Character of the coffee, although this style of roast might not appeal to your palate. In fact, at this degree of caramelization you have (perhaps) caramelized 50% of the sugars. Non-caramelized sugars cup sweeter than the bittersweet-bitter caramelized ones, so here you have a compliment of the presence of both, lending dimension to the cup character. The roast temperature window of 400-425 represents the "peak of flavor" roast temperatures.
Full City Roast, Full City+ Roast*
415-425 degrees f. internal bean temperature, 438-448 f by thermo-probe
A lighter Full City roast, where the coffee has just barely showed signs of 2nd crack -a snap or two-, or that 2nd crack is imminent, and the roast is stopped. The actual temperature that second crack normally occurs is higher: 446 degrees f internal bean temperature. But in fact second crack is a little less predictable than first crack, in my experience. Why? It could be explained as this: first crack is the physical expansion of the coffee seed as water and carbon dioxide split and CO-2 outgassing occurs. Second Crack is the physical fracturing of the cellular matrix of the coffee. This matrix is wood, also called cellulose, and consists of organized cellulose that reacts readily to heat, and not-so-organized cellulose that does not. Since every coffee is physically different in size and density due to the cultivar, origin, altitude, etc. it might make sense that the particular cell matrix is different too, and not as universally consistent in reactiveness as H-2O and CO-2.
|*City, Full City note: We are dividing up the roasts around City and Full City into finer distinctions using the + sign. So City (or sometimes "true City roast" means the coffee has fully cleared 1st crack, and the roast is stopped (about 425-430 f). City+ means the coffee has cleared first crack, and time is allowed for an even bean surface appearance to develop, about 435f usually. Full City, or "true Full City" is where the coffee is roasted to the verge of 2nd crack without entering it, which is about 440-445f and enters it slightly, but the coffee is dumped/roast is ended at that point, so the batch has no momentum to truly enter 2nd crack, roughtly 445-448f. Beyond that and we are talking Vienna roast in my book. The temperatures in this paragraph are not internal bean temperatures, but probed bean temperatures from my Probat roaster.|
Full City Roast+, on the dark side
430-445 degrees f. internal bean temperature, 450 f by thermo-probe
This stage represents the darker side of a Full City roast, where the coffee has barely entered 2nd crack, and 10 seconds of snaps are heard, and the roast is then stopped.
450-465 degrees f. internal bean temperature, 455-465 f by thermo-probe
An aggressive Full City roast and beyond into the Vienna stage (also called Continental) is where you begin to find Origin Character begin to be eclipsed by Roast Character. If you buy coffee for its distinct origin qualities, it makes sense that heavy roasting is at odds with revealing the full effect of the differences we can sense in coffee due to distinct origins.
Espresso is not a roast. But Northern Italian style espresso is usually roasted to 440-460 internal bean temperature. Southern Italian (Scura) is generally a French Roast.
Full French Roast -Italian Roast
475-510 degrees f. internal bean temperature, 470-490 f by thermo-probe, or more (!)
Sugars are heavily caramelized and begins to be degraded; the woody bean structure is carbonizing, the seed continues to expand and loose mass, the body of the resulting cup will be thinner/lighter as the aromatic compounds, oils, and soluble solids are being burned out of the coffee and rising up to fill your house with smoke.
520-530 degrees f. internal bean temperature, fire coming soon!
At this point the coffees flavor-contributing compounds are severely degraded, the cellular matrix of the coffee is completely ruptured, the soluble solids content of the coffee is diminished (so the cup will not have body and taste "thin"), and fire will soon ensue... the mythic and dreaded "third crack".