|The Fine Art and Precise Science of Roasting|
© 2007 The George Howell Coffee Company
Roasting unlocks and frames a coffee's flavor potential; it is a science and an art that requires loads of experience, concentration and split second timing. Roasting is also the means by which the roaster imprints his/her signature. How bright or muted will the coffee be? How much depth or 'chiaroscuro' should the roaster impart to the coffee’s intrinsic flavor? Should there be a touch of bitterness at the end?
Green coffee beans feel like rounded cold pebbles in the hand; they are very hard and nearly half the size they will be after roasting.
There are different kinds of roasters. The classical machine is a rotating metal drum operating by conduction (hot surface) and convection (heated air passing through the rotating, tumbling beans). Our roaster is this type. Achieving the right balance is difficult but well worth the effort. Another type operates strictly by convection typically floating on a bed of hot air. Many inexpensive home roasters are this type (like modified popcorn cookers). They permit very clean expressions of a coffee's flavor profile. They can also lack a certain dimensionality that is given by traditional roasters, which impart a slight roast variation between surface and interior, achieving more depth and highlighting acidity. The roaster walks a fine line.
It can take anywhere from 2 minutes (jet-roasting) to 20 minutes or more to roast a batch of coffee. The extremes produce equivalently terrible results on quality coffee. Both fail to develop a fine coffee's complexity (over 600 flavor components); a fine coffee’s flavor profile is demolished beyond recognition. Some modern machines, designed for the mass market, are continuous rather than batch roasters; green coffee enters one end of a giant corkscrew and emerges in short order through the other side roasted in one unending sequence.
The Three Stages of a Roast
Stage One - During the first stage the green beans are dried by gently vaporizing away stored free water molecules - while using the water’s conductivity to pass heat throughout the bean and begin effective roasting in the second stage, a very fine line! The beans turn from bluish-green to yellow-orange in this first stage and it is easy to singe their surfaces, imparting a bitter aftertaste to the coffee brew, or to bake the coffee, resulting in a flat, lifeless cup.
Stage Two - The second stage of actual roasting begins about half way through the roast. As the beans turn from yellow to light brown, going past 320 F, they begin cooking from within; escaping steam and carbon dioxide begin building pressure on the beans’ cell walls. When the beans’ temperature passes 380F, their surfaces, increasingly brittle, begin to expand and crack open along their center lines, emitting popping sounds. Roasters call this moment 'the first pop'. The roast is now nearing the first of several stations where it can be stopped; it is up to the roaster to decide which one, as the beans go from darkening tones of caramelized browns and beyond - to carbonized glistening black.
Stage Three - The third stage is terminating the roast. With bean temperature at 420 F or higher, it is now critical to stop the beans from cooking as quickly as possible. The traditional way is to release them into a perforated tray that is stirred while drawing the cool surrounding air through the beans with a fan below.
The Coffee Roaster's Palette
There are three key roasts. Each roast covers a certain range suited for different tasting purposes.
1. Full Flavor Roast
A few minutes after the first popping the beans reach their maximum aromatic development, ideal for the unique floral-and-fruit expressions of fine single origin coffees. The cellular structure of the beans is intact with no oils bleeding to the surface. The beans can show a slight irregularity of tone. The range of what we call Full Flavor roast has been traditionally referred to as City to Full City roasts. The lighter end of this spectrum is ideal for drip and vacuum coffeemakers while slightly darker-hued beans offer deeper caramel notes, working well with French Press machines.
These coffees, roasted lightly, are meant to be savored as they cool in the cup, approximating the intensity of wine only as they reach room temperature, when our tastes buds are fully receptive. These roasts are too light for espresso brewing with one exception: softer coffees with low acidity, such as certain Brazils, can be roasted to this color for a North Italian style espresso, giving wonderfully sweet flavors without hint of bitterness or excessive acidity.
2. Vienna Roast
As the beans darken still further a second popping occurs, sounding more like a sizzling. Now the actual cellular structure begins to crack, allowing the oils enveloping the aromatics to gradually bleed to the surface, imparting a nice even sheen to the beans. A light Vienna roast is achieved just as the second popping commences – and can go all the way to full second “crack”, releasing still more oils and their precious volatile perfumes. Vienna roast coffee brewed in a drip coffeemaker is characterized by a semi-sweet caramel roastiness coupled with dramatic dulling of acidity – or liveliness - with a rise in bitter flavors towards the far-back of the tongue. It is commonly served in many quality restaurants these days because of its safe character, offering a certain generic richness, neither offending with any assertiveness nor particularly inspiring. Nevertheless, the right beans, roasted to a light Vienna, can make a fine French Press or a particularly rich espresso, where, through high-pressure percolation, enough acidity is squeezed out to make a complex, balanced demitasse delight.
3. French Roast
As the roaster goes beyond the second popping thick smoke begins oozing out of every opening and the coffee veers towards its version of a heavy Lapsang Souchong. Any remaining aromatics are now burned off, replaced by carbony smoke leaving a strong bitter aftertaste. Such coffees are best drunk hot when a certain cutting yet elegant bitterness can cut through the rich aftertaste of a heavy meal or dessert. When the cup cools coarser flavors come into play.
Hot French-roasted beans spill into the cooling tray, shining with thick bright oil. This quickly evaporates and the coffee stays a dull blackened-brown for the next dozen or so hours. Then the oils reappear in such profusion that the beans stick together. Rancidity can easily set in.
Back in the early days of The Coffee Connection, in the late 1970’s, before we knew much, we roasted one coffee beyond French to what we called Italian Roast, which was as close to jet-black as we could get. Italian Roast turned to Pompeii Roast once too often with the Fire Department converging on a mini inferno. We survived and over time evolved towards subtler pleasures.