How to Define Coffee Roast Levels and Their Flavors

Ever wonder why your 'light roast' from one café tastes drastically different from another’s — or why some baristas swear by dark roasts while others champion light? You’re not alone. Roast level debates aren’t just personal preference — they’re rooted in inconsistent terminology and real chemical changes in the bean.

The key? Scientific roast measurement like Agtron numbers. These quantify surface color and caramelization, turning vague terms like 'city' or 'French roast' into objective data. Here’s how roast levels truly work, what they mean for flavor, and why the debate isn’t going away anytime soon.

How Roast Levels Are Scientifically Defined

For decades, U.S. roasters used informal terms — Cinnamon (lightest), City (light), Fully City (medium-dark), and Dark roast (including French and Italian) — to describe roast levels. But these terms varied wildly by region: what’s ‘light’ on the West Coast might be ‘dark’ back East. That changed with the Specialty Coffee Association of America (SCAA), which introduced Agtron numbers based on infrared measurement of bean surface caramelization.

These numbers reflect the degree of Maillard reaction and caramelization on the bean’s surface. Higher values = less caramelization = lighter roast. Lower values = deeper roast = more structural and flavor change.

How Roast Level Alters Coffee Flavor

Your coffee’s acidity, bitterness, sweetness, and aroma all shift with roast depth. Here’s what actually happens:

• Acidity: Higher in light roasts, decreases as roast gets darker. If you love citrus, berry, or stone fruit notes, opt for a lighter roast.
• Body & Mouthfeel: Lighter roasts tend to have a lighter, tea-like body; darker roasts develop more viscosity and heaviness (often described as ‘bold’ or ‘chewy’).
• Caffeine: Contrary to myth, light roasts actually contain slightly more caffeine than dark roasts. Caffeine breaks down under prolonged heat.
• Aroma & Sweetness: Fruity, floral, and fermenty notes shine in lighter roasts. Darker roasts emphasize smoky, caramelized, and bitter-chocolate characteristics, along with a heavier ‘roasty’ finish.
• Oil Development: Surface oils emerge around the start of the second crack (around Agtron 40), typically associated with darker roasts. Oils can impact crema in espresso and mouthfeel in filter.

The Great Light vs Dark Roast Debate

Roasters don’t just disagree on taste — they clash over fundamental philosophy. The debate often splits along regional lines and technical approach.

The Light Roast Camp

Northern Italy, parts of the U.S. East Coast, and roasters like Illy, Green Mountain, and Vivace (despite being in Seattle) favor stopping the roast just before the coffee beans release oils — usually before or at the start of the second crack, achieving Agtron values around 40. They argue that:

• Oils carry aromatic compounds; keeping them inside preserves more delicate flavors.
• The coffee achieves optimal balance between acidity and sweetness.
• Body and finish are cleaner and more expressive of origin character.

They criticize dark roasting as unnecessarily burning off those aromas, calling oil on the surface a loss of flavor potential.

The Dark Roast Camp

U.S. West Coast and Southern Italian roasters — including Peet’s Coffee (San Francisco), Caffe D’Arte (Seattle), and Beans & Machines — believe coffee should be roasted well into or through the second crack until oils surface. Their espresso roasts often score below Agtron 35, with some beans (like their Antigua) reaching extreme levels like Agtron 18.

They argue:

• Oils enhance boldness, bitterness, and the classic ‘roastiness’ sought in traditional espresso.
• Light roasts can taste one-dimensional or overly acidic if the beans are of lower quality.
• It takes advanced skill to navigate the volatile second-crack phase without producing burnt or ashy cups.

Peet’s, in particular, is known for extended roasting at high temperatures (over 200°C for 15+ minutes) while avoiding excessive bitterness — a technique they’ve perfected over decades.

What Really Determines Roast Quality?

Roast level is not just about time or temperature — it’s about how the roaster manages the bean through critical phases like first crack, Maillard transition, and second crack. Whether you prefer your coffee at Agtron 65 or 25, execution matters more than ideology.

Light roasts can be thin and sour if underdeveloped. Dark roasts can be bitter and ashy if over-roasted. Great roasting, regardless of level, requires precision, batch control, and sensory judgment.

Frequently Asked Questions

What is an Agtron number and how is it used in coffee?

An Agtron number measures the color and caramelization level of a coffee bean’s surface using infrared spectroscopy. It’s a standardized way to define roast degree: higher numbers (70+) indicate very light roasts (Cinnamon), while lower numbers (35 or below) indicate dark roasts (French/Italian). It removes subjective terms and provides objective data for consistency.

Does light roast coffee have more caffeine than dark roast?

Yes. Caffeine content is slightly higher in light roasts than in dark roasts because prolonged roasting breaks down some caffeine molecules. While the difference per bean is small, light roasts technically retain more caffeine than heavily roasted ones.

Why do some roasters stop before the second crack?

Roasters who prefer lighter profiles (like those in the City to Fully City range) stop roasting just before or at the beginning of the second crack (around Agtron 40). They aim to preserve acidity, origin flavors, and aromatic compounds that can be lost when oils emerge and the roast deepens further.

What happens during the second crack in coffee roasting?

The second crack signals a more advanced roast stage where the bean structure breaks down further, oils migrate to the surface, and the roast flavor becomes more dominant. This typically occurs around Agtron 40 or lower, leading to fuller body, bolder bitterness, and less acidity — hallmarks of dark roasts.

Which is better: light roast or dark roast?

Neither is inherently better. Light roasts highlight origin characteristics, acidity, and floral or fruity notes. Dark roasts emphasize boldness, body, caramelized sugars, and roast-driven flavors. Preference is subjective and depends on the coffee’s origin, processing, and brewing method.

Do darker roasts have more body?

Generally, yes. Darker roasts develop a heavier, more viscous mouthfeel due to chemical changes in the bean’s cellulose structure and the release of oils. This gives them a fuller, often described as 'chewier' or 'smoother' body compared to lighter roasts.

Recommended FrontStreet Beans for Roast Exploration

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for bright, juicy acidity in a light city-level roast; their Colombia Huila for balanced medium body around a Fully City profile; and their Sumatra Mandheling, often roasted to a darker Vienna/French style with low acidity and heavy mouthfeel. Each highlights 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.