Nothing influences the taste of coffee more than roasting. The same green coffee can be roasted to taste grassy, taste baked, taste sour, taste bright and dry, taste full-bodied and mellow, taste rounded and bitter-sweet, taste charred. In appearance roasted beans can range from light brown with a dry surface through dark brown with an increasingly oily surface to black with an almost greasy look.
Changing Roast Traditions
Until recently preferences in roast style, like so many other cultural choices, were traditional. Traditional preferences are the basis of many of the names used in the contemporary American coffee business to describe style of roast: New England (light), American (medium), Viennese (slightly darker), French (still darker), Italian (still darker again), etc.
It is difficult to determine "best" style of roast. One of the many pleasures of home roasting is experimenting for yourself to determine what the "best" roasting style is for you. Of course one of the frustrations of home roasting is that once you get a batch of beans that tastes exactly the way you want them to you may have trouble precisely duplicating the procedure that produced them. But if you are at all systematic you can come very close to consistency, and home roasting is for romantics and adventurers anyhow. Those concerned purely with uniformity probably should stick to buying coffee from the store.
Bad by Any Standard
There are some clear parameters to good roasting, however, boundaries which, if transgressed, produce roasts that are bad by almost anyone's standard.
In roasts that are too light, in which the internal temperature of the beans never rises above 390F and the color remains a pale brown, the flavor oils stay undeveloped and the coffee will taste grassy, sour, and without aroma. In roasts that are too dark, in which the internal temperature of the beans has soared above 480F and the color is definitely black, most of the flavor oils will have been burned out of the bean and the woody parts of the bean itself may be charred. Such coffee tastes thin-bodied, burned, and industrial.
Another way coffees can be roasted definitively badly is either by baking them by holding them too long at too low a temperature, or by scorching the outer surfaces of the beans. Both mistakes are easy to commit for beginning home-roasters.
But so long as a roast avoids such extremes, only cultural preference and personal taste can determine which style is ultimately "best."
Names and Roast Styles
Currently-used names for roast styles come from two sources. One source is the general roasting preferences of various nations of coffee drinkers -- Italian, French, etc. The other grew up within the American coffee profession during the late 19th and early 20th centuries.
Geographical Roast Names
Let's take a quick run through the common roast names first, beginning with those that derive from coffee-drinking geography, since these are the names you are most likely to see on coffee bags and bins.
New England (light brown, dry surface)
American (medium brown, dry surface)
Viennese (medium dark brown, possibly flecks of oil on surface)
French (moderately dark brown, light oil on surface)
Espresso (dark brown, surface can range from very oily to barely slick depending on roast procedure)
Italian (dark, blackish brown, definite oily surface; most roasting establishments stop here)
Dark French or Spanish (very dark brown, almost black, very oily).
Traditional American Roast Names
There is another naming system haunting the aisles of coffee stores, however, one based on traditional American roasting terminology stretching back to the 19th century. It breaks out about like this:
Cinnamon (very light)
Light (light end of the American norm)
Medium-high (American norm)
City; high (slightly darker than norm)
Full city (definitely darker than norm; sometimes patches of oil on surface)
Dark (dark brown, shiny surface; equivalent to espresso or French)
Heavy (very dark brown, shiny surface; equivalent to Italian).
Numbers to the Rescue: The Agtron/SCAA Roast Color Classification System
The Specialty Coffee Association of America (SCAA) has recently released a kit for classifying roast based on precise machine reading of color.
The eight reference points in this classification system have no names, only numbers, and are matched with eight color disks. A sample of a roasted coffee can be matched with a color disk, thus assigning it an approximate number on a scale variously termed a chemistry index or Agtron gourmet scale. These color-disk (or color-tile) numbers run from #95 (lightest roast) through #85 (next lightest) at intervals of ten down to #25 (darkest common roast).
Talking About Taste
Here are a few of the most important terms for talking about differences in taste among green coffees and roast styles. I've disregarded popular terms that are self-evident or have no clear, consensus meaning (rich, floral, fruity, buttery, etc.).
Acidity; acidyOne of the most important tasting categories in coffee, and one of the most likely to be misunderstood. Neither acidic nor sour, an acidy coffee is brisk and bright. The darker a coffee is roasted, the less acidy it becomes. However, strong acidity in a green coffee may show up in a dark roast as sharpness or pungency.
Body; mouthfeelBody is the sensation of heaviness in the mouth; it also registers as a rich, full feeling at the back of the palate. Body is a sensation, an element of taste, not a measurable fact. As coffee approaches a medium-to-dark brown roast, body increases. As it passes into a very dark roast (Dark French or Spanish roast) body decreases.
AromaAlthough this term is self-evident in its general definition, it is important in discussions of roast. Aroma is less developed in very light roasts, peaks in intensity in medium to medium-dark roasts, and falls off in very dark roasts.
ComplexityAnother obvious yet useful term. A complex coffee allows certain strong sensations such as acidity and sweetness to coexist. It presents a wide range of sensation, and often doesn't reveal itself immediately and definitively. Complexity is undoubtedly at its peak in the middle ranges of roast style, from medium through the moderately dark to dark roasts used for espresso. Most blends aim to increase complexity.
DepthDepth describes the resonance or sensual power behind the sensations that drive the taste of the coffee. It is a tricky and subjective term, but it tries to get at the way certain coffees open up and support their sensations with a sort of ringing, echoing power, whereas others simply present themselves to the palate and then stand pat or even fade.
Varietal distinction, varietal characterThese terms seem to have migrated over to coffee from wine-tasting relatively recently. They describe qualities that distinguish one unblended, green coffee from another when the coffees are brought to the relatively light "cupping" roast used in professional coffee evaluation.
BalanceDescribing coffees in which the acidity is strong but not overwhelming, the body substantial, and no taste idiosyncrasy dominates.
Wild; natural; earthyA slight sour twist to the acidity is the best verbal description I can produce. Once you identify this taste syndrome you'll know it forever. I enjoy wild-tasting coffees; they remind me that I'm drinking something that comes from the earth. But I'm a romantic. If this taste is too pronounced it becomes an outright defect.
CleanIn some respects this term describes qualities that are the opposite of wild or natural. Clean-tasting coffees are free of defects, shadow undertones, or varietal distractions.
These are words specifically related to the overlay of taste that style or degree of roast contributes to green coffees.
SweetIn medium-dark through moderately dark roasts (Viennese through espresso) the development of sugars combined with the partial elimination of certain bitter flavor components like trigonelline give the cup a rounded, soft taste and rich body without flatness. Some coffees come to a sweeter dark roast than others.
Pungent, pungencyThese words are my choice to describe the distinctive, bitterish twist that dark-roasting contributes to taste. Any lover of dark roasts knows and honors this sensation.
Roast taste; bittersweetTerms describing the characteristic collective flavor complex of darker roasts. The acidy notes are gone, replaced by pungent notes combined with a subtle, caramel sweetness. Bittersweet is my term; some people call this often unnamed group of sensations roast taste or the taste of the roast.
BreadyA bready taste manifests in coffees that have not been roasted long enough or at a high enough temperature to bring out the flavor oils.
BakedAnother term for maltreated coffee. The coffee has been held too long in the roaster at too low a temperature; the taste in the cup is flat and without aroma.
Roast Styles and Flavor
Now let's look at how some of these key categories -- acidity, body, aroma, varietal distinction, and roast taste -- transform as coffee is brought in stages from a very light to a very dark roast style.
The most lightly roasted coffee (usually called cinnamon; internal bean temperature at conclusion of roast below 400F; SCAA color tile #95) is very light brown in color, will display a strong, sometimes sour acidity, little aroma, an often grainy taste, and thin body. The surface will be dry.
As the coffee achieves a more complete but still relatively light roast (New England, light; concluding internal bean temperature around 400F; SCAA color tile #85), the acidy notes will be powerful, and the varietal characteristics, which often are nuances of acidity, will be pronounced. The body will be developed, but not as fully as it will become in a somewhat darker roast. The surface of the bean remains dry, as the flavor oils continue to develop in tiny pockets inside the bean.
At a moderately light to medium-brown roast (light, medium, American; concluding internal bean temperature between 400F-415F; SCAA color tiles #75 through #65) the acidity will be bright but less overpowering, the varietal characteristics still pronounced, and body fuller. For most traditional East-Coast American coffee-drinkers this style represents a "good" coffee taste.
At a slightly darker, medium-brown roast (medium, medium high, American, city; concluding internal bean temperature 415F-435F; SCAA color tile #55) acidity remains strong though perhaps richer, varietal characteristics muted but still clear, and body still fuller. This is the traditional roasting norm for most of the American west.
At a full city, often labeled Viennese roast (concluding internal bean temperature 435F-445F; between SCAA color tiles #55 and #45), acidity is slightly more muted and body slightly heavier. The surface of the bean may remain dry, or oils may appear in tiny droplets or patches as they begin to rise from pockets inside the bean to its surface.
At a moderately darker roast (espresso, European, high; concluding internal bean temperature 445F-455F; between SCAA color tiles #45 and #35), the acidity is largely folded into a general impression of richness, the varietal characteristics muted virtually beyond recognition, the body full, and the bittersweet notes characteristic of dark-roasted coffees rich and resonant. At this roast the surface of the bean always displays some oil, ranging from a few droplets to a shiny coating.
When coffee is brought to a definitely dark roast (French, Italian, dark; concluding internal bean temperature 455F-465F; SCAA color tile #35) the bittersweet or dark roast taste completely dominates, the body begins to thin again, and all remaining varietal character and acidy notes are transmuted inside the pungent richness of the dark roast flavor, which may range from rounded and mellow (in less acidy coffees) to bordering on bitter (in coffees that begin very acidy). The surface of the bean will be bright with oil.
With very dark brown roasts (Italian, Dark French, Spanish, heavy; concluding internal bean temperature 465F-475F; between SCAA color tiles #35 and #25) the body continues to thin as more and more of the oils are evaporated by the roast, the bitterish side of the bittersweet equation becomes more dominant, and a slight charred taste may appear. The bean is shiny with flavor oils driven to the surface.
The ultimate dark roast, almost black (Dark French, Spanish; concluding internal bean temperature 475F-480F; SCAA color tile #25) is definitely a special taste. The body is even thinner, more bitter and less sweet, and burned or charred notes dominate. All coffees regardless of origin tend to taste about the same. The surface of the bean is bright with oil. Home roasters typically have an opportunity to sample this ultimate dark roast, since sooner or later we all produce a batch whether we plan to or not.
Beyond this point the coffee is definitively burned: it has no body, tastes like charred rubber, the oils are driven off the surface of the bean, and the roast is worthless.
Time/Temperature Ratio and Other Subtleties
All roast styles differ in taste depending on how the roast is achieved. Coffee brought to a given roast color quickly -- by higher roast temperature or a combination of higher temperature and rapidly moving air currents -- will usually preserve more acidy notes than will coffee brought to the same degree of roast at lower air temperatures over a longer period of time. On the other hand, a slower roasted coffee tends to be fuller in body and more complex in taste.
Time/Temperature Ratios and the Home Roaster
Your ability to experiment with subtler taste differences related to the way you achieve a given roast style depends above all on the equipment you use.
I propose four technologies for home roasters in Home Coffee Roasting: 1) stove-top crank corn poppers; 2) hot-air corn poppers and similar fluid-bed roasting devices; 3) gas ovens; and 4) electric convection ovens. Each tends to produce a roast emphasizing certain taste characteristics.
Those who like a bright, acidy coffee are probably best served by a fluid-bed roasting technology as represented in hot-air corn poppers and similar home roasters.
Those who like a more idiosyncratic roast taste with heavier body and a fuller profile may be best off with an old-fashioned stove-top corn popper that achieves a given roast more slowly and allows the roasting smoke to work around the beans.
Coffees prepared in gas ovens often display a striking complexity and depth of flavor because the irregularity of the roast coaxes a wider range of taste out of the coffee than do methods that produce a more regular, uniform roast. The relatively long roast times in gas ovens also promote a rather full body and relatively rounded, low-acid flavor profile.
Finally, there are electric convection ovens. The extremely long, slow roast produced by these appliances creates a clean-tasting, full-bodied, but very low-acid cup. Coffees roasted in electric convection ovens will taste dull to most palates, although some may enjoy their gentle, understated sweetness.
Green Coffee Characteristics and Roast Style
The moisture content and hardness of green coffee beans effect how quickly they roast and how they respond to various roast temperatures. The moister and denser the bean the somewhat slower it will roast and/or the higher the temperature needs to be in the roast chamber. More technically inclined roasters precisely measure the density and/or moisture content of the bean and modify their roasting procedure accordingly.
Such exact accommodations are not an option for most home roasters. However, there are a few rules of thumb based on the age of a green coffee and how it has been handled that can be usefully followed by the home roaster. These are included in later excerpts from Home Coffee Roasting.