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Kona Coffee Roast Guide

We are currently working on our Interactive Coffee Roasting guide. Until then, enjoy some information about the stages of roasting.

1. Green unroasted coffee   75 °F / 24 °C
This is a wet processed batch of green coffee at room temperature. These seeds have pulped from coffee cherries, dried and had the parchment and silver skin removed. Each photo here is of  different coffee seeds from the batch roasted so size and shape will vary from seed to seed.

2. Starting to pale   270 °F / 132 °C

Drum roasters take a long time to transfer heat to coffee so there is little change in the first few minutes. In an air roaster coffee gets to this stage much faster because of the efficient heat transference of the rapidly moving air stream, so the whole warm-up phase can be as fast as two minutes. The beans are losing water that is boiling off due to the heat.

3. Early yellow stage   327 °F / 164 °C
At this point the coffee is still losing water in the form of steam and no physical expansion of the bean has taken place. 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   345 °F / 174 °C
The beans in the roast are starting to assume a browner color, and a marbling appearance is starting to emerge. No bean expansion has occurred 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   370 °F / 188 °C
First crack is drawing near at this point. Some bean expansion is visible as the central crack in the coffee has opened slightly. The coffee releases some silverskin or chaff, which will start to go up the smokestack of the roaster.

6. Brown Stage   393 °F / 200 °C
Now the roasting beans are right at the door of first crack. 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. First crack begins   401 °F / 205 °C
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). At the point of first crack the internal bean temperature would be around 356 °F / 180°C – it’s surprising how the internal temperature lags the roaster temperature, but that is the process of roasting for you.

8. First crack is under way   415 °F / 213 °C
As first crack continues the coffee still appears mottled and uneven in color. The coffee starts expanding in size and shows visible cracks. The amount of chaff in the crease of the seed is noticeably less.  First crack is an exothermic reaction: the beans are giving off heat. But then the beans 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 °F / 170-204°C internal bean temperature) a roast that loses heat will taste "baked", perhaps due to the disruption of long-chain polymerization. The melting point of sucrose is 370 °F / 188°C and corresponds to this window of temperatures when caramelization begins.

9. First crack finishes 426 °F / 219 °C
Finally!  We have some coffee that we can drink.  This is considered, or called, a City Roast coffee. First crack is done and the roast is stopped. Notice the bean surface is smoother somewhat from expansion but still has darker marks in the coffee, like a finely etched pattern. The edges of the seed are still fairly hard. At this point the coffee starts giving off carbon dioxide gas from reactions within the bean.

10. City Plus Roast stage   435 °F / 224 °C
City Plus means the coffee has cleared first crack, and time is allowed for an even bean surface appearance to develop.  There are only very small changes between the #9 picture and the #10 one, notably the edges of the bean are a bit softer. The whole stage between the first and second crack is a short period (15 to 30 seconds) where a lot is happening chemically to the beans. The coffee gains heat once again until its woody cellulose matrix, the bean structure itself, begins to fracture ... that is, the Second Crack stage.

11. Full City roast --   On the verge of Second Crack 444 °F / 229 °C
Beans #11 represent a Full City roast; the coffee is on the verge of second crack. The beans have a slight sheen of oil and the edges are softer. The internal bean temperature for second crack normally is 446 °F / 230°C. But in fact second crack is a bit less predictable than first crack due to the fact that first crack is the physical expansion of the coffee seed as water and carbon dioxide split and CO2 out gassing starts. Second Crack is the physical fracturing of the celllose matrix of the coffee. This matrix is both organized cellulose that reacts readily to heat, and not-so-organized cellulose that does not. Since every coffee bean is physically different in size and density due to the cultivar, origin, altitude, etc., it make sense that the particular cell matrix is different too, and not as universally consistent.

12. Full City Plus roast -- First audible snaps of Second Crack 454 °F / 234 °C
The darker side of a Full City roast is Full City Plus, where the coffee has barely entered second crack. A few snaps are heard, and the roast is then stopped. Second crack may continue into the cooling phase - this is called "coasting". The more effective and rapid the cooling your system can achieve - the better your ability to stop the roast at the degree you want.

Compare the full size images from the Full City roast and the Full City Plus roast, and you can probably see a difference.  The Full City Plus roast is a bit fuller with more small cracks on the face (or flat side) of the bean.

13. Vienna - Light French roast --  Second crack is under way   465 °F / 241 °C
The Vienna stage (also called Continental) or Light French stage is where you begin to find Origin Character eclipsed by Roast Character. A dark or heavy roast is at odds with buying coffee for its distinct origin qualities. Dark roast coffees tend to taste more like each other - as the differences due to distinct origins are obscured by the carbony roast flavors. Nevertheless, some coffees can be excellent at this stage (Kona coffees are not one of those).

By the way; “Espresso” is not a roast. But Northern Italian style espresso is usually roasted to 440 - 446 °F / 227-230°C internal bean temperature. Southern Italian (Scura) expresso is generally a Light French Roast or a tad darker.

14. Full French roast 474 °F / 246 °C
The second crack is very rapid and is nearing its end.  Sugars in the beans are now heavily caramelized (read as burned) and are degraded; the woody bean structure is carbonizing and 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 as really great smelling smoke. 474 °F is well beyond any roast we do here in Kona. This stage is shown here only for completeness.  Notice how dramatic the change is from the photo #13 - all that happened in less than 30 seconds in the normal roaster!

15. Fully carbonized 486 °F / 252 °C
Some call this Italian or Spanish roast, an insult to either or both! At this stage, the coffee can be over 25% ash; it is carbonized, dead, charcoal. You will never see this stage of roasting in Kona unless the roast master has gone off and ignored the roasting process.  And finally. . .

16. Imminent fire ... 497 °F / 258 °C
These beans are right at the verge of fire - in fact you can actually start a fire with a large batch if you dump the coffee out of the roast drum onto the cooling tray. The sudden rush of oxygen might be the only needed ingredient for cafe del fuego. Kids, grab your marshmallows! Hope you like 'em smokey!  Needless to say, this roast level is full-on carbon and you can write your name with a coffee bean. The bean size here is smaller that photo #15 due to the randomness of the seeds selected to photograph - coffee does not actually get smaller at this stage: it is just a lump of carbon by now.

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