Methods & Equipment
Despite the simplicity of the requirements, at this writing the home appliance world still has not given us an effective, inexpensive home roasting device. Consequently, most approaches described here are improvisations. They will produce excellent coffee, however.
The simplest approach of all is dumping the beans in a skillet and stirring them until they're brown. This method does roast coffee, just as it did for hundreds of years before people started inventing machines to do it better. But the coffee produced by skillet-roasting surely will disappoint 20th-century sophisticates who have come to expect something tastier than the often scorched and uneven beans that satisfied our 18th-century forbears.
Let's review what needs to take place in coffee roasting:
The beans must be subjected to temperatures between 460F and 530F (240C and 275C). These temperatures can be lower if the air around the beans is moving faster, as in fluid-bed roasting apparatus, or higher if the air is moving sluggishly;
The beans (or the air around them) must be kept moving to avoid uneven roasting or scorching;
The roasting must be stopped at the right moment and the beans cooled promptly. (Some provision must be made to vent the roasting smoke.)
Roasting with Hot-Air Corn Poppers
Both hot-air corn poppers produce a very consistent, uniform roast with bright acidity, good aroma, and a clean taste. The body may be slightly lighter than in coffees roasted by other methods, and the taste perhaps less complex.
Use only poppers that introduce the hot air from the sides of the popping/roasting chamber. Do not use designs in which the hot air issues from grill-covered openings or slots on the bottom of the popping/roasting chamber. With such styles it is possible that roasting chaff could collect around the heating elements, and eventually cause the device to ignite.
Hot-air poppers can be easily modified to incorporate a metal candy/deep-fry thermometer. This simple (two-minute) modification enables you to monitor the progress of the roast by the inner temperature of the beans rather than their outer color or appearance. Kenneth Davids outlines the installation process in his book, Home Coffee Roasting: Romance & Revival.
Roasting in a Gas Oven
Achieving an acceptable roast in a given gas oven usually requires patient experiment with that particular appliance. Nevertheless, the flexible, precise control of temperature provided by gas ovens is an advantage, as are the venting arrangements, which carry the roasting smoke outside, usually with considerable efficiency. Most gas ovens will roast a pound or more of coffee at a time, and again, the flavor of oven-roasted coffee can be startlingly good.
Style or Color of Roast
The simplest way to translate your personal taste in roast into home practice is to find a store that sells a whole-bean coffee roasted in a style you like, buy some, and attempt to duplicate it at home.
Timing the Roast
Coffee roasting is considerably more forgiving in this respect than many kitchen procedures. With fresh pasta, for example, a thirty-second distraction can turn al dente into al mush, whereas with coffee roasting a minute or two delay merely produces a darker roast that is still drinkable and enjoyable.
You need to learn to read the roast with "your senses," as most roasters have done throughout history. The principles are simple: look, smell and listen.
You need sample beans, already roasted to the color you prefer, to which you compare the color of your own beans as they roast and gradually deepen in color. Place these sample beans where you can see them easily during the roasting session.
After you begin the roasting process nothing dramatic will happen for some three to ten minutes while a grassy or burlap-like odor rises from the beans. There is no need to watch the beans during this early stage of the roast, but if you do you will notice that they are changing in color from a grey-green to a light, golden brown.
Eventually steam, still smelling like grass or burlap, will begin rising from the beans. Gradually this steam will darken and take on a coffee-like odor. On the heels of the appearance of the darker, coffee-smelling roasting smoke you will hear a subdued crackling sound, confirming the onset of pyrolysis, or the inner transformation of the bean.
From this moment forward you must depend mainly on sight. Assuming your goal is a medium to medium-dark (full-city) roast, wait about thirty seconds (hot air popper) to two minutes (gas oven) after the crackling sets in and begin peeking at the beans to monitor their color. How soon after the onset of pyrolysis you need to start your visual inspection of the beans depends partly on how dark you want to roast. Roasts develop rather quickly in hot-air corn poppers, later in gas oven roasting.
Regardless of whether you are pursuing a lighter or darker roast you will need to visually observe the beans as they approach the critical moment when they match the color of your sample. When they are about the same or a little lighter than your sample you must stop the roast and begin the cooling process, usually by dumping the roasting beans into a colander or bowl. I realize that "the same or a little lighter" is hardly precise language, but you'll learn.
Never abandon roasting beans. This is a particularly important caution with hot-air popper methods. You should not even leave the room until the heat is off and the session over. If coffee beans are abandoned inside a hot roasting chamber long enough they become semi-flammable.
The gas oven method allows you a bit more leeway. By controlling the variables and keeping a few simple records, it is possible to determine approximately when to end a roasting session by elapsed time, thus permitting the use of a kitchen timer to alert you to the impending moment of truth.
Concluding and Cooling the Roast
Cooling the hot beans rapidly and efficiently is one of the most important steps in home roasting, since coffee continues to roast from its own internal heat long after it has been removed from external heat. Coffee that is allowed to coast down to room temperature of its own accord will taste dramatically inferior to coffee that is promptly and decisively cooled.
Many home roasters prepare small batches of a few ounces of beans per session, so simply dumping the beans into a colander and stirring or tossing them is sufficient cooling procedure. This procedure needs to take place over a sink or out-of-doors, so that the roasting chaff that floats free of the beans will not litter the counter or stove-top.
You also can initiate the cooling process by water-quenching, just as professional roasters often do. A pump or trigger spray dispenser, the kind with a nozzle that adjusts to a fine mist, works very well. Simply fill the dispenser with distilled or filtered water, and while stirring or tossing the hot beans subject them to a few seconds of light, intermittent mist. Perform this procedure immediately after roasting, and be careful not to overdo the application of water by spraying too long or using too coarse a spray.
Getting Out the Chaff
Removing the chaff using the hot air popper is no problem because the moving air removes the chaff during the roasting process. In other methods, tossing or stirring the beans in a large colander facilitates cooling, and rids the beans of most of their chaff. Any amount that is left in the beans will have little to no effect on flavor. The single most important piece of advice to home roasters in regard to chaff is not to be obsessive about it.
Two Ways of Looking at Roasting Smoke
The good news is that roasting smoke smells wonderful while you're roasting. To some people it still smells wonderful two hours later, but to many of us it becomes stale and cloying.
Hot-air poppers can be used on a porch or balcony in clement weather, or operated directly under a kitchen exhaust fan. Don't try to use them outside in temperatures under 50F however, since the cold may prevent them from achieving effective roast temperatures. Ovens that are components of kitchen ranges are well-vented and carry the smoke outside.
Those who like light-to-medium roast styles will have less to be concerned about than those who prefer darker roasts, since beans produce their most voluminous and intense smoke as they are carried to darker styles.
Accommodations for Differences Among Green Coffees
All coffees roast somewhat differently. If you have been roasting one coffee regularly and you begin roasting another, do not expect it to behave exactly like the first. For example, decaffeinated beans roast dramatically (15% to 25%) faster than non-treated beans, and must be observed with great care after pyrolysis sets in to avoid over-roasting.
Roasting Blends of Beans from Different Origins
The separate batches of beans from differing origins that together make upmost blends can be combined before or after roasting. If the batches are combined before roasting the look of the roast may not be absolutely uniform, but the cup quality usually will be fine. The only situation in which two components must be roasted separately is in the case of blends of decaffeinated and regular beans, since decaffeinated beans roast much more quickly than untreated beans.
Systematic Roasting: Controlling Variables
Some home roasters enjoy improvising; some relish the challenge of system and precision. A methodical approach is definitely the best way to achieve intimate knowledge of roast and coffee taste.
Informative experiment depends on control of four roasting variables:
The amount of coffee roasted;
The temperature inside the roasting chamber;
The identity of the green coffee (in particular its approximate moisture content, largely a condition of age);
The time or length of the roast.
This list of variables assumes that you are using the same roasting method or technology (i.e. gas oven, hot-air corn popper, etc.) for all of your experiments. The taste of a given roast style gotten by different methods will vary, sometimes greatly.
Like any good investigator, you need to control three of the four variables while systematically varying the fourth, meanwhile keeping careful record of the results. A sample form for recording notes on your roasting experiments is included in Home Coffee Roasting: Romance & Revival.
The two variables that you are most likely to experiment with are the identity of the green coffee and the length of time the roast is sustained.
If you are consistent from session to session with roast-chamber temperature, quantity of coffee roasted and quench method you can obtain useful results by recording only five to six variables: the identity of the green coffee, the date of the roast, the final bean temperature (if your method permits), the elapsed time of the roast, the appearance of the roasted beans, and your tasting notes.