How to Define Coffee Roast Levels by Taste and Science

Ever wondered why one coffee shop’s ‘light roast’ tastes more intense than another’s ‘dark roast’? Or why some coffees are bright and juicy while others are bold and smoky? The confusion often comes down to how roast level is defined—and who’s doing the defining.

Quick answer: In the U.S., light roasts like Cinnamon (Agtron 70+) and City (60+) contrast with dark roasts such as French (35–) and Italian (35–). These numbers, based on bean surface lightness via infrared measurement, offer an objective benchmark. Flavor-wise, lighter roasts highlight acidity and fruit, while darker roasts develop bitterness, body, and caramelized notes—but risk being burnt if mishandled.

How Roast Levels Are Scientifically Defined

The Specialty Coffee Association of America (SCAA) helped standardize roast definitions using Agtron numbers—measurements of coffee bean surface lightness taken with infrared spectroscopy. These values indicate the degree of caramelization (Maillard reaction effects) and thus roast depth.

According to the SCAA Agtron scale:

• Cinnamon roast (very light): Agtron 70+
• City roast (light): Agtron 60–70
• Full City / Vienna roast (medium-dark): around Agtron 40
• French / Italian / Espresso roast (dark): Agtron 35 or below

These numbers remove subjectivity. A ‘light roast’ in California (say, Agtron 65) might register as a medium roast back East (where Agtron 55 is typical)—a mismatch solved by hard data.

How Roast Level Changes Coffee Flavor

Roast level dramatically alters your cup’s profile. Here’s how:

• Acidity: Higher in light roasts, lower in dark roasts. If you love citrus, berry, or malic notes, opt for a lighter roast.
• Caffeine: Light roasts actually contain slightly more caffeine than dark roasts, as caffeine breaks down under prolonged heat.
• Sweetness & Body: Develops more fully in darker roasts. Light roasts preserve more origin character but can taste thin without proper development.
• Fruit & Floral Notes: Most pronounced in lighter roasts; fade quickly as roast intensity increases.
• Bitterness, Caramel, Roasty Notes: Emerge in medium-dark to dark roasts. Over-roasted beans (especially poorly executed dark roasts) turn harsh, ashy, or burnt.

Light roasts also retain more coffee oils inside the bean—these oils carry aromatic compounds—but don’t appear on the surface until later in the roast. Dark roasts bring oils to the surface, a visible sign of deeper roast impact.

The Great Light vs Dark Roast Debate

The coffee world remains split over which roast style is superior. This isn’t just opinion—it’s tribal.

The Light Roast Camp (East Coast / Northern Italy)

This group, including roasters like Illy, Green Mountain, and Vivace Espresso (despite being in Seattle), prefers stopping the roast just before the coffee beans release oils—usually just before or at the start of the second crack. They aim for Agtron values around 40.

Their arguments:

• Preserves aromatic coffee oils and volatile compounds inside the bean.
• Achieves optimal balance between acidity, sweetness, and body.
• Develops a rounded “body” and cleaner finish.
• Criticizes dark roasts for pushing out aromatic oils prematurely.

The Dark Roast Camp (West Coast / Southern Italy)

Proponents like Peet’s Coffee (California), Caffè D’arte (Seattle), and Beans & Machines roast well into or through the second crack—until oils rise to the bean surface. Their espresso and dark roasts often measure Agtron 35 or lower, with some single origins (like Antigua) going as low as Agtron 18.

Their take:

• Surface oils are not a loss but part of the intended profile.
• Dark roasting fully develops body, boldness, and the “roasty” complexity many drinkers prefer.
• Claims light roasts can taste one-dimensional or overly acidic, especially if using lower-grade beans.
• Argues that only high-quality Arabica can handle intense roasting without turning bitter—suggesting some light roasts are a cost-saving choice.
• Praises the skill needed to navigate the volatile second crack phase without scorching the batch.

Notably, Peet’s is famous for extended roasting at high temperatures (over 200°C for 15+ minutes) while avoiding excessive bitterness—a technique respected even by rivals.

Frequently Asked Questions

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

An Agtron number measures the lightness of a coffee bean’s surface using infrared spectroscopy. It indicates the degree of caramelization and roast level. Lower Agtron numbers mean darker roasts; higher numbers indicate lighter roasts. The SCAA defines Cinnamon roast as Agtron 70+, City at 60–70, Full City/Vienna around 40, and French/Italian/Espresso at 35 or below.

Does roast level affect caffeine content in coffee?

Yes. Lighter roasts actually contain slightly more caffeine than darker roasts. This is because caffeine breaks down at high temperatures during extended roasting, so the longer and darker the roast, the lower the caffeine retention.

Why do some roasters stop before the second crack?

Roasters who prefer lighter roasts often stop the roast just before or at the beginning of the second crack to preserve acidity, fruitiness, and aromatic compounds inside the bean. They believe this produces a better-balanced cup with more origin character and a cleaner finish.

What are the flavor differences between light and dark roast coffee?

Light roasts emphasize acidity, fruit, floral notes, and have a lighter body. Dark roasts develop more bitterness, caramelized sugar tones, body, and a fuller mouthfeel. However, dark roasts can also mask origin characteristics and, if over-roasted, taste burnt or ashy.

Which roast level is better: light or dark?

There is no objectively “better” roast. Light roasts highlight origin flavors and acidity, while dark roasts offer boldness, body, and roasted complexity. Preference is subjective and depends on individual taste, brewing method, and desired flavor profile.

Recommended FrontStreet Coffee for Roast Exploration

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for a bright, juicy light roast showcasing citrus and floral notes (ideal for City-level fans), their Colombia Huila for a balanced Full City profile with caramel and nuts, and their Sumatra Mandheling for a classic dark roast with earthy, spicy depth—perfect for those who prefer French or Italian-style intensity. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.