1.
Green Coffee Beans 0:00 - 75 f
This is a wet processed,
Jamaican Blue Mountain Coffee, a accidental blend I have had sitting around.
Each photo here are different coffee seeds from the batch I roasted so size
and shape will vary seed to seed.
2.
Starting to pale 4:00 - 270 f
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 so much faster because of
the efficient heat transference of the rapid moving air stream, so the whole
warm-up phase can be as fast as two minutes.
3.
Early yellow stage 6:00 - 327 f
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 6:30 - 345 f
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.
5.
Light Brown stage 8:00 - 370 f
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.
6.
Brown Stage 9:00 - 393 f
Now we 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.
1st crack begins 9:20 - 401 f
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.
8.
1st crack under way 10:00 - 415 f
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 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 10:40 - 426 f
This is considered a City Roast. 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.
City+ 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 above and this 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.
This image represents a Full City
roast; the coffee is on the verge of 2nd crack. This might be hard to judge the
first few times you roast; after a while, you will have a feel for it. The
beans are have a slight sheen of oil and the edges are softer.
The internal bean temperature for
second crack normally is 446 degrees Fahrenheit. But in fact second crack is a
bit less predictable than first crack, in my experience. Why? It could be 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 cellulose 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 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.
The darker side of a
Full City roast is Full City +, where the coffee has barely entered 2nd 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 you’re cooling - the
better your ability to stop the roast at the degree you want.
Compare the full size
images from the Full City roast and this one, and I think it is easy to see a
difference. Well, maybe not easy, but the Full City+ roast is a bit fuller,
more small cracks on the face (or flat side) of the bean.
The Vienna stage (also
called Continental) to 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. Nontheless, some coffees are
excellent at this stage.
By the way; Espresso
is not a roast. But Northern Italian style espresso is usually roasted to 440 -
446 internal bean temperature. Southern Italian (Scura) is generally a Light
French Roast or a tad darker.
Sugars are 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 to fill your
house with smoke.
Notice how fast and dramatic the
change is from the previous photo - all that happened in less than 30 seconds!
15. Fully carbonized 13:00 - 486 f
Some call this Italian
or Spanish roast, an insult to either!
At this stage, the coffee can be
over 25% ash; it is carbonized, dead, charcoal.
16. Imminent fire ... 13:30 - 497 f
This bean is right at
the verge of fire - in fact you can actually start a fire with a large batch
once you dump the coffee out of the roast drum into the cool tray. 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 get smaller at this stage...
