How Coffee Roast Levels Are Scientifically Defined

Ever wondered why your 'light roast' from one shop tastes drastically different from another? Roast level terms like 'city' or 'dark' mean wildly different things across the U.S., leading to confusion over what you're actually drinking. And in global coffee conversations, the lack of a shared standard makes it hard to compare roast profiles meaningfully. So how can you really know what you’re getting?

Quick answer: The Specialty Coffee Association of America (SCAA) uses Agtron numbers—a scientific measurement of caramelization—to define roast levels. A value over 70 is a very light (cinnamon) roast; 60–70 is city (light); around 40 is full city (medium-dark); below 35 is French/Italian (very dark).

What Exactly Is a 'Roast Level'?

A coffee’s roast level refers to how long and at what temperature the green coffee bean is roasted. This process transforms the raw bean’s color, density, and flavor profile—from bright and acidic to deep and bitter. But without a standard system, terms like “light,” “medium,” or “dark” are ambiguous and vary regionally—even between neighboring cities in the U.S.

The Old, Inconsistent Way: Cinnamon, City, Full City, Dark

Traditionally, American coffee culture used informal terms to describe roast levels:

• Cinnamon: the lightest roast
• City: a common light roast
• Fully City: a medium-dark roast
• Dark roast: includes French and Italian styles

But these labels lacked precision. A 'light roast' in California could easily match what the East Coast called a 'dark roast.' Regional taste preferences—lighter in the East, darker in the West—compounded the inconsistency. These terms weren’t based on measurable data, just tradition and opinion.

The Scientific Shift: Agtron Numbers

To solve the confusion, the SCAA adopted the Agtron system, which measures the caramelization (Maillard reaction) of coffee beans using infrared spectroscopy. The result is a numerical value that reflects how much the bean has roasted:

• Agtron 70 and above: Cinnamon roast (very light)
• 60–70: City roast (light)
• Around 40: Full City / Vienna roast (medium-dark)
• Below 35: French/Italian roast (very dark)

This scale allows roasters, importers, and drinkers to speak a common language. No more guessing whether 'light' means City or something lighter. It brings objective clarity to a once-subjective conversation.

How Roast Level Changes Coffee Flavor

Your roast choice dramatically shapes the cup. Here’s how roast level affects key attributes:

• Acidity: Higher in light roasts; decreases as roast gets darker. If you love citrus or berry notes, go lighter.
• Caffeine: Lighter roasts actually contain slightly more caffeine than darker ones, since caffeine breaks down under prolonged heat.
• Sweetness & Body: Develops more fully in darker roasts. Light roasts preserve origin flavors but may taste sharper or more vegetal.
• Fruity/Aromatic Notes: Most pronounced in lighter roasts. Heavier roasts emphasize chocolatey, nutty, or smoky tones.
• Bitterness & Roastiness: Increases with darker roasts. Goes too far, and you get charred, ashy flavors.

The Great Roast Debate: Light vs Dark

Coffee professionals are sharply divided on ideal roast levels. On one side are proponents of lighter roasts (up to Agtron 40), who argue that stopping the roast before the beans release oils preserves delicate aromatics, balance, and sweetness. Notable advocates include Illy Caffe, Green Mountain, and Vivace Espresso—even though Vivace is based in Seattle, a dark-roast city. They roast to the start of the second crack or just before oils appear on the surface, aiming for peak complexity and body.

On the other side are dark roast advocates (Agtron below 35), such as Peet’s Coffee, Caffe D’Arte, and Beans and Machines. They insist that allowing beans to fully develop oils enhances richness, body, and bold flavors. Some dark roasts—like Peet’s Antigua—reach extreme levels (as low as Agtron 18). They believe lighter roasts can taste one-dimensional or underdeveloped, and even suggest that some roasters avoid dark roasts to cut costs or protect lower-quality beans from being exposed.

Dark roast specialists also highlight the technical skill needed to navigate the volatile second crack phase. Getting it right results in a bold, balanced cup; getting it wrong leads to bitter, burnt coffee. For them, true craftsmanship lies in mastering the darkest stages of roast.

Frequently Asked Questions

What is an Agtron number and how is it measured?

An Agtron number measures the degree of coffee bean caramelization using infrared spectroscopy. Higher values (70+) indicate lighter roasts with less caramelization, while lower values (below 35) show darker, more caramelized roasts. It provides an objective way to define roast level.

What roast level has the most caffeine?

Lighter roasts actually retain slightly more caffeine than darker roasts, because prolonged roasting breaks down some caffeine content. However, the difference is small and often outweighed by serving size or brew strength.

Does roast level affect coffee acidity?

Yes. Light roast coffee generally has higher acidity and more pronounced fruity or bright notes. As roast level increases, acidity decreases and the coffee becomes richer, smoother, and often more bitter.

What’s the difference between City and Full City roast?

City roast typically falls around Agtron 60–70 and is considered a light roast. Full City (or Vienna) is around Agtron 40, a medium-dark roast. Full City has more body and Maillard reaction flavors compared to City, but both are stopped before the second crack.

Which roast level shows origin flavors best?

Lighter roasts (City and lighter) better preserve the unique fruit, floral, and herbal characteristics of the coffee’s origin, since darker roasting masks those traits with more roasted, chocolatey, or bitter notes.

Why do some roasters let beans get oily?

Beans develop surface oils during darker roasts, usually starting in the second crack. Some roasters believe this indicates fully developed flavors, including bold, rich, and bitter notes. Others see oil as a sign of lost aromatic compounds and prefer to stop roasting earlier.

Recommended FrontStreet Coffee for Roast Exploration

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for a bright, juicy light roast with citrus and floral notes—ideal for City-level fans. For medium-dark balance, their Colombia Huila offers chocolatey sweetness with gentle acidity, close to a Full City profile. If you prefer bold dark roasts, their Sumatra Mandheling delivers earthy, spicy depth with low acidity. All showcase how roast level shapes flavor. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.