[스크랩] 로스팅 단계

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1. Green unroasted coffee
This is an Organic coffee, a accidental blend I have had sitting around a few months. Sadly, if we mess up coffee here, there is nothing I can do with it, even though it is fine coffee involved. I wanted to find a charity I could roast our mistake blends for... Anyway, each photo here are different coffee seeds from the batch I roasted so size and shape will vary seed to seed. I actually cannot remember what exact coffees were in this mistake blend. I can say by appearance it is not super high-grown coffee, and I suspect a portion of the blend is actually Kona.


2. Starting to pale
Odd looking seeds - the nearer might be a Kona Typica and the farther is a rounded shape, perhaps the traditional Bourbon cultivar or Mundo Novo. As you have figured out, I am not pulling samples at regular intervals (no sense in that). I am pulling them when the coffee has reached an identifiable and significant visual stage. Bigger drum roasters take a long time to transfer heat to coffee so there is little change in the first few minutes. Also, keep in mind I wasn't trying to do a good roast on this batch, just trying to make it turn brown so I could take pictures...


3. Early yellow stage
At this point the coffee is still losing water in the form of steam and no physical expansion of the bean has taken place. In an air roaster coffee gets to this stage so much faster because of the efficient heat transference of the rapid moving air stream. The coffee has a very humid, hay-like smell at this point. All of these warm-up stages leading up to first crack are part of an endothermic process, as the coffee takes on heat, leading to the first audible roast reaction, the exothermic 1st crack.


4. Yellow-Tan stage
The roast is starting to assume a browner color, and a marbling appearance is starting to emerge. No bean expansion yet. The first "toasty" smells (toasted grain, bread) can be detected, and a bit less wet, humid air coming off the coffee. Note that some coffees turn a brighter and more distinct yellow at this time, such as Costa Rican and Mexican coffees.


5. Light Brown stage
First crack is drawing near at this point. Some bean expansion is visible as the central crack in the coffee has opened slightly. This allows the coffee to release some of the silverskin in the form of chaff that has been attached to the bean in the folds of the crack.


6. Brown Stage
Now we are right at the door of first crack. In a short time the coffee has browned considerably, which is partly due to browning reactions from sugars, but largely due to another browning reaction called the Maillard Reaction (which also is responsible for browning of cooked beef!)


7. 1st crack begins
At this point, the very first popping sounds of the First Crack can be heard. This sound can be similar to popcorn pops, in distinction to the sound of the Second Crack, which has a shallower sound, more like a snap.


8. 1st crack under way
As first crack continues 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 internal bean temperature) 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.


9. 1st crack finishes
This is considered a City Roast, a bean appearance where the surface has smoothed somewhat from expansion but still has darker marks in the coffee, like a finely etched pattern. 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.


10. City+ roast
The stage between the first and second crack is a short period of further endothermy as the coffee gains heat once again until it reaches the point where its woody cellulose matrix, the bean structure itself, begins to fracture ... that is, the Second Crack. You notice a darkening in a very short period of time and small change in temperature between the #9 picture above and this one.


11. Full City roast On the verge of 2nd crack
This image represents 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.


12. Full City+ roast First audible snaps of 2nd crack
This image 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. Compare the full size images from the lighter Full City roast and this one, and I think it is easier to see a difference. Well, maybe I shouldn't say it is easy, since the main cue that would distinguish the difference between the two is audible, not visual.


13. Vienna - Light French roast 2nd crack is under way (This is my darkest espresso roast)
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.

By the way; 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.


14. Full French roast 2nd crack is very rapid, nearing its end.
Sugars are heavily caramelized (read as burned) and are 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.


15. Fully carbonized
Some call this Italian or Spanish roast, an insult to either!


16. Immanent fire ...

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