How Coffee Roast Levels Are Actually Defined by Agtron Numbers

Ever wondered why your "light roast" from a West Coast café tastes far darker than one from the East? Or why terms like "Full City" or "French roast" don’t mean the same thing everywhere? You’re not alone. For decades, U.S. coffee professionals have used subjective roast names that vary wildly by region and personal taste—leading to confusion and inconsistent expectations.

Here’s the clear answer: modern specialty coffee in the U.S. uses Agtron numbers—a scientific measurement of coffee bean surface color and caramelization—to define roast level objectively. These numbers eliminate guesswork and standardize what "light," "medium," and "dark" really mean.

What Are Agtron Numbers and How Do They Define Roast Levels?

The Specialty Coffee Association of America (SCAA) introduced Agtron values as an objective way to measure roast degree. Agtron machines shine infrared light on roasted coffee beans and measure how much light is reflected—essentially gauging how much the bean has caramelized during roasting. The higher the number, the lighter the roast; the lower the number, the darker the roast.

This system provides a shared language that removes regional bias and helps both producers and consumers understand exactly what roast they’re dealing with.

How Roast Level Changes Coffee Flavor and Caffeine Content

Roast level dramatically affects how coffee tastes—and even how much caffeine it contains. As a rule, acidity (that bright, fruity tang) decreases as roast level increases. So, if you enjoy crisp citrus or berry-like flavors, aim for a lighter roast. On the flip side, heavier roasts bring out deeper, more intense flavors such as caramel, chocolate, and smokiness, along with that classic “bold” mouthfeel.

Caffeine content also shifts: lighter roasts retain slightly more caffeine than darker ones, because some caffeine breaks down under prolonged high heat. However, the difference is small—don’t expect a dramatic jolt just from choosing light roast.

Flavor notes evolve with roast level too. Lighter roasts preserve more origin characteristics and develop subtle fruit, floral, or herbal tones. They may lack the heavy body or syrupy sweetness of darker roasts, but they highlight the bean’s intrinsic qualities. Darker roasts, meanwhile, tamp down origin nuances in favor of roast-driven traits like bitterness, bittersweet chocolate, and a heavier mouthfeel. But if the roast isn’t executed well, you risk ending up with a burnt, ashy cup.

Why the Light vs. Dark Roast Debate Still Rages

The debate over ideal roast level is one of the oldest and most polarizing in coffee. On one side are proponents of lighter roasts, mainly based in Northern Italy and the U.S. East Coast. They typically pull the roast around Agtron 40—stopping just before or as the first signs of coffee oils appear on the bean surface. This group includes respected names like Illy Caffe, Green Mountain, and Vivace Espresso. Their argument? Oils carry delicate aromatic compounds. Letting beans reach first crack or early oil development maximizes balance between acidity and sweetness, while preserving body and complexity.

These roasters often criticize darker roasts for pushing oils to the surface, claiming it leads to a loss of aromatic intensity. They see their approach as preserving the coffee’s inherent character.

On the opposite end are the dark roast advocates, concentrated in Southern Italy and the U.S. West Coast. Players here include Peet’s Coffee (San Francisco), Caffe D’Arte (Seattle), and Beans and Machines. These roasters typically roast well into the second crack, aiming for Agtron values below 35—even dropping as low as 18 for certain beans like Antigua. They argue that darker roasts unlock deeper flavors, enhance body, and develop the characteristic boldness many drinkers associate with espresso or “classic” coffee.

They also reject the idea that oil surfacing ruins flavor, insisting instead that lightly roasted beans are underdeveloped—lacking depth, balance, and the rich, bold profiles they value. Some critics even claim that light roasting is partly a cost-saving move, since only the finest Arabica beans can handle intense heat without turning bitter.

Peet’s, especially, is known for mastering long, high-temperature roasts—sometimes over 200°C for 15 minutes—that produce bold, smooth cups without harshness. Their success has helped elevate dark roasting as an art form in its own right.

Frequently Asked Questions

What is an Agtron number and how is it measured?

An Agtron number measures the reflectance of infrared light off a roasted coffee bean’s surface, indicating its degree of caramelization. Higher numbers (70+) mean a very light roast; lower numbers (35 or below) indicate a dark roast. SCAA uses these values to provide a standardized way to define roast levels objectively.

Which roast level has more caffeine, light or dark?

Light roasts generally contain slightly more caffeine than dark roasts, because caffeine breaks down at high temperatures during extended roasting. However, the difference is minimal and shouldn’t be the sole reason for choosing one over the other.

Does roast level affect coffee flavor?

Yes. Lighter roasts tend to highlight acidity, fruitiness, and origin flavors, while darker roasts emphasize body, bitterness, caramel, and roast-driven notes like chocolate or smoke. Over-roasted beans can taste burnt or ashy.

What is the difference between City and Full City roast?

City roast is a light roast, usually with an Agtron number of 60 or above, offering brighter acidity and more origin character. Full City (or Vienna roast), around Agtron 40, is medium-dark, balancing acidity with more body and sweetness.

Why do some roasters let beans develop oils and others don’t?

Roasters who stop before oils surface (usually lighter roasts) believe it preserves aromatic compounds and optimizes balance. Dark roast roasters let beans reach or pass first and second cracks, letting oils emerge to enhance body and boldness, which they see as essential to full flavor development.

Which is better: light roast or dark roast?

Neither is universally better—it depends on personal taste. Light roasts offer more acidity and nuanced origin flavors; dark roasts deliver bold, rich, and sometimes sweeter profiles. It’s subjective, and both have their merits.

FrontStreet Coffee Beans for Exploring Roast Profiles

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for a bright, floral light roast showcasing the clarity of City-level profiles. For something more balanced, their Colombia Huila offers a medium-bodied cup with juicy acidity—ideal for Full City fans. And if you prefer bold, the FrontStreet Brazil Natural highlights chocolatey sweetness in a darker Vienna-to-French range. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.