Dropping Roast Knowledge...
Ever wanted to know how your favorite morning beverage comes to be? We LOVE this visual example from the amazing resource Sweet Marias. Read on to learn about the stages coffee goes through from green to 'imminent fire'.
Coffee stages, green to burnt!
1. Green unroasted coffee
This is a wet processed, Central American coffee. This is how your favorite morning beverage begins!
2. Starting to pale
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
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
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. The coffee releases some silverskin or chaff, the thin papery membrane surrounding the bean.
6. Brown Stage
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
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
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
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. Roasting to City Roast is a growing trend among west coast and urban centered roasters. A City roast will give the taster the greatest level of acidity present in the bean. This can be an acquired taste for some, similar to the recent trend in a substantial use of hops in NW beers as well! Those PNW folks like to go big.
10. City+ roast
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.
Note; many of our beans at Bestslope are roasted to this level as we feel it provides a nice balance from the sometimes biting acidity present in a City roast and the sweeter caramelized flavors that develop as the roast progresses.
11. Full City roast
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 farenheit. 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 outgassing 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 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+ roast
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 your 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.
13. Vienna - Light French roast
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.
14. Full French roast
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
At this stage, the coffee can be over 25% ash; it is carbonized, dead, charcoal.
16. Imminent fire ...
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. The sudden rush of oxygen might be the 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 get smaller at this stage...
Know your roasts- how this all translates to taste
Most roasters have specialized names for their favored roasts and there is very little industry standardization. This can cause some confusion when you’re buying, but in general, roasts fall into one of four color categories — light, medium, medium-dark and dark.
Many consumers assume that the strong, rich flavor of darker roasts indicates a higher level of caffeine, but the truth is that light roasts actually have a slightly higher concentration.
The perfect roast is a personal choice that is sometimes influenced by national preference or geographic location. Within the four color categories, you are likely to find common roasts as listed below. It’s a good idea to ask before you buy. There can be a world of difference between roasts.
Light brown in color, this roast is generally preferred for milder coffee varieties. There will be no oil on the surface of these beans because they are not roasted long enough for the oils to break through to the surface.
▪ Light City
▪ Half City
This roast is medium brown in color with a stronger flavor and a non-oily surface. It’s often referred to as the American roast because it is generally preferred in the United States.
▪ City to City +
Medium dark roasts
Rich, dark color, this roast has some oil on the surface and with a slight bittersweet aftertaste.
▪ Full City
This roast produces shiny black beans with an oily surface and a pronounced bitterness. The darker the roast, the less acidity will be found in the coffee beverage. Dark roast coffees run from slightly dark to charred, and the names are often used interchangeably — be sure to check your beans before you buy them!
▪ New Orleans