Understanding Coffee Roasts

Barbara Rolek
Roasted coffee beans with coffee cup

Navigating the coffee aisle at your local store can be confusing when faced with the sheer number of brands lining the shelves. But brand, country of origin and type of bean are secondary to how the coffee is roasted.

What Roasting Does to Coffee Beans

Roasting is a heat process, according to National Geographic, that turns spongy, soft green coffee beans into the aromatic, dark brown, crunchy beans everyone knows and loves.

Most roasting machines are heated to a temperature of about 550 degrees F, according to the National Coffee Association (NCA). The beans are kept moving throughout the process, often in a rotating cylinder, to keep them from burning. After roasting, they are flash-cooled and are ready to move on to grinding and brewing.

The desired color and strength of the end product determines how long the beans are roasted and the way in which they are ground.

Coffee Roast Categories

In general, coffee roasts fall into one of four color categories, notes both National Geographic and the NCA's Coffee Roasts Guide -- light, medium, dark (also known as medium-dark) and darkest (also known simply as dark). The longer a bean is roasted, the more oily it becomes and the acidity of a light roast is replaced with bitterness in a dark roast. If you like your jolt of caffeine to still taste of coffee, then a light roast might be for you. Or are you the type who doesn't mind feeling a little wired from the charred overtones of a finely ground dark roast? Choosing the right roast should be the first thing to consider when buying coffee.

Light Roasts

Lightly roasted coffee allows the country of origin and true bean flavor to shine through because it's roasted only for about seven minutes, before the oil has a chance to rise to the surface. Contrary to most beliefs, light roasts have slightly more caffeine than dark roasts, notes the NCA.

  • Color: Light brown, no oil on the surface
  • Flavor: Mild
  • Acidity: High
  • Roasting time: About seven minutes
  • Common names: Light City, Half City, Cinnamon, New England

Medium Roasts

Coffee beans roasted to the medium stage get about nine to 11 minutes in the roaster. At this point, the oil locked inside the beans starts to rise to the surface giving a more pronounced flavor and aroma to the coffee than a light roast.

  • Color: Medium-brown
  • Flavor: Full-bodied, sweeter than light roast, aromatic
  • Acidity: Slightly less acidic than light roast
  • Roasting time: About nine to 11 minutes
  • Common names: City, American, Breakfast, Brown

Dark Roasts

Coffees in this category are dark in color and have an oily appearance on the surface of the bean because they are roasted for 12 to 13 minutes, enough time for the oil to emerge. They have a slightly bittersweet aftertaste.

  • Color: Rich, dark color with some oil on the surface
  • Flavor: Full-bodied, bittersweet aftertaste, aromatic
  • Acidity: Acidity not detectable
  • Roasting time: About 12 to 13 minutes
  • Common names: Full City, High, Continental, New Orleans, European, Viennese, French

Darkest Roasts

Coffee beans roasted for up to 14 minutes fall into the darkest category. The beans are black, almost charred in appearance, and have a distinctly oily surface. The acidity, coffee bean flavor and country of origin of a light roast are almost completely replaced with bitterness and caramelized overtones.

  • Color: Black, slightly charred-looking beans with an oily surface
  • Flavor: Pronounced bitterness, smoky, tastes more of roasting than the bean flavor
  • Acidity: Acidity disappears and is replaced with bitterness
  • Roasting time: About 14 minutes
  • Common names: Italian, Espresso

Acidity in Coffee

In the culinary sense, the term "acidity" has somewhat of a negative connotation. When it comes to coffee, however, acidity is not a bad thing. The levels of acidity are high in lightly roasted coffee, allowing the true flavor of the bean and its country of origin to shine through. The darker the roast, the less acidic and the more bitter the coffee will be.

Coffee beans used for light and medium high-acidic roasts are usually Arabicas, grown at high altitudes.

Arabica Beans vs. Robusta Beans

Of the approximately 6,000 species of coffee in the world, the two most commonly used for drinking are Arabica and Robusta. What sets these two species apart is their country of origin (Hawaii, Ethiopia, Brazil, Vietnam, etc.) and how they are roasted, and then eventually ground.

Arabica Beans

Arabica trees are grown at high altitudes and, thus, their beans are more expensive because of labor-intensive harvesting techniques.

The beans from these trees produce a fine, soft, high-acidic, aromatic coffee that represents about 70% of the world's coffee production, reports the Specialty Coffee Association. Varieties include Bourbon, Typica, Caturra, Mundo Noo, Tico, San Ramon, Jamaican Blue Mountain and others.

Robusta Beans

Robusta trees are grown at low altitudes, making it cheaper to harvest. Thirty percent of the world's coffee production comes from Robusta beans, notes the NCA, and are grown in Central and Western Africa, parts of Southeast Asia, including Indonesia and Vietnam, and in Brazil.

These beans are less flavorful, less aromatic, harsher and have twice the caffeine of Arabica. These beans, considered inferior to Arabica, are used primarily in blends, instant coffees and for espresso grinds.

Coffee Is a Personal Choice

Just as there is no right or wrong when it comes to wine choices, the same is true of coffee. Coffee is a highly personal, subjective matter. It's not a bad idea to taste all four categories of roasts -- light, medium, dark and darkest. Choose the roasting degree that appeals to you most. Then expand on the countries of origin within that color category. It might be surprising that you have favorites in all four roasting categories.

Understanding Coffee Roasts