How Coffee Roast Levels Are Defined and What They Taste Like

If you’ve ever wondered why one roaster’s ‘light roast’ tastes deeper than another’s ‘medium,’ you’re not alone. Despite common terms like 'city' or 'full city,' there’s no universal standard—making roast definitions confusing, especially across regions. So how do you really know what you’re getting when you buy a bag labeled 'light' or 'dark'?

The answer lies in measurable data: the Agtron number, a scientific scale that quantifies roast level based on coffee bean surface color and caramelization. Agtron values range from 70+ for very light roasts down to 35 or lower for dark roasts, removing guesswork.

What Is a Coffee Roast Level?

Coffee roast level refers to how long and at what temperature green coffee beans are roasted. The roast profoundly affects flavor, aroma, body, and even caffeine content. Common terms like 'light,' 'medium,' and 'dark' are widely used but vary by region and roaster. Without a standardized system, one roaster’s 'city' might be another’s 'full city.'

How Roast Levels Are Scientifically Defined: The Agtron Scale

In response to inconsistent terminology, the Specialty Coffee Association of America (SCAA) popularized the use of Agtron numbers—a spectrophotometric measurement of bean surface color reflecting the degree of caramelization (Maillard reaction products) and roast development. These numbers provide a consistent, objective way to define roast level:

• Agtron 70 and above: Cinnamon roast (very light)
• Agtron 60–69: Light roast, often called City
• Agtron around 40: Vienna roast or Fully City
• Agtron 35 and below: Dark roast, including French and Italian styles

This scale removes regional bias. For example, what a West Coast US roaster calls a 'light roast' (say, Agtron 65) might register as a 'medium' or even 'city+' elsewhere. Agtron brings clarity.

How Roast Level Affects Coffee Flavor and Caffeine

Roast level dramatically influences your cup. Here’s how:

• Acidity: Higher (more acidic, fruity, bright) in lighter roasts; decreases as roast darkens.
• Body & Mouthfeel: Lighter in light roasts; increases (becomes richer, heavier) as roast darkens, peaking around Full City to Vienna.
• Flavor Notes: Light roasts preserve more origin characteristics—floral, fruity, and herbal notes. Dark roasts develop smoky, bitter, chocolatey, or even burnt tones. Aromas like fruity esters fade with darker roasting.
• Caramelization & Roast Development: Deeper roasts undergo more Maillard reaction and sugar caramelization, contributing to bold flavors but reducing origin complexity.
• Caffeine: Contrary to popular belief, lighter roasts actually contain slightly more caffeine than darker ones. Caffeine is marginally degraded by prolonged heat, meaning darker roasts have marginally less.

Light roasts also retain more of the coffee’s natural lipids (oils), which can contribute to a livelier cup but may also taste sharper or more acidic to some drinkers. Dark roasts bring out heavier, syrupy body and more intense bitterness—but risk tasting ashy or roasty if overdone.

The Great Light vs Dark Roast Debate

The question of ideal roast level isn’t just technical—it’s cultural, even tribal. In the US and Northern Italy, many roasters prefer lighter roasts stopped just before or at the start of the second crack. These roasts (often Agtron 40–60) highlight origin qualities, preserve coffee oils inside the bean, and are said to deliver a better balance of acidity and sweetness. Notable proponents include Illy, Green Mountain, and Seattle’s Vivace Espresso—even though it’s in dark-roast-heavy territory.

These roasters argue that letting oils migrate to the bean surface (a sign of over-roasting or nearing second crack) leads to loss of aromatic compounds. Their light roasts aim to finish extraction just before maximum oil exudation, preserving both flavor complexity and body.

On the other side are proponents of darker roasts—common in Southern Italy, the US West Coast, and among classic espresso-focused roasters. Roasters like Peet’s Coffee (California), Artisan Coffee (Seattle), and Beans & Machines roast well into or past the second crack until oils rise to the bean’s surface. Their dark roasts often register Agtron 35 or lower—including espressos as low as Agtron 18 (like their Antigua offering).

This camp believes that allowing the roast to progress through and past the second crack develops deeper flavors: bittersweet chocolate, bold body, intense crema potential for espresso, and a rounded, “complete” taste. They reject the idea that early stopping preserves quality, instead accusing light roasts of being underdeveloped, overly sharp, or boring. Some even argue that lighter roasts are a cost-saving measure, as only high-quality beans can withstand darker roasts without turning unpleasantly bitter.

PDT (Peet’s), known for roasting well beyond second crack for over 15 minutes at high temperatures, maintains that their dark roasts achieve a rich yet non-bitter cup through skillful control—a technique they’ve honed through custom-roasted machinery.

Frequently Asked Questions

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

An Agtron number measures the color of roasted coffee beans using infrared spectroscopy, reflecting how much caramelization has occurred. It’s a scientific way to define roast level. Higher numbers (70+) indicate very light roasts (like Cinnamon), while lower numbers (35 or below) indicate dark roasts (like French or Italian). It removes subjective terms and standardizes roast measurement.

What’s the difference between a light roast and a dark roast?

Light roasts are stopped earlier in the roasting process, typically just before the first crack or right after. They feature higher acidity, more fruity or floral notes, lighter body, and more caffeine. Dark roasts are roasted longer, often through or past the second crack, resulting in bolder, bitterer flavors, heavier body, less acidity, and slightly less caffeine.

Does roast level affect caffeine content?

Yes. Lighter roasts generally contain slightly more caffeine than darker roasts. This is because caffeine is slightly degraded by prolonged exposure to high heat during extended roasting. However, the difference is small and often overshadowed by bean variety and brew strength.

Which roast level best highlights the coffee’s origin flavors?

Lighter roasts (City to Cinnamon, Agtron 60–70+) are better at preserving the unique fruity, floral, or herbal notes of the coffee’s origin. Darker roasts tend to mute these subtleties in favor of roasted, chocolatey, or bitter flavors developed during prolonged heat.

Why do some roasters let beans get oily and others don’t?

Coffee beans release natural oils as they roast. Lighter roasts typically stop before these oils reach the surface (Agtron 40–60), preserving certain aromatics and balance. Darker roasts continue roasting until oils emerge (Agtron 35 or lower), which some roasters believe contributes to richer body and complexity, especially for espresso.

Is French roast the darkest possible roast?

French roast is very dark (Agtron 35 or lower), but some roasts go even darker, such as Italian roast or competition-style dark roasts (e.g., Agtron 18). These extremely dark roasts are used mostly for espresso or bold brewed coffee and can taste smoky or burnt if not carefully managed.

Recommended FrontStreet Beans for Roast Exploration

Try FrontStreet Coffee’s Ethiopia Yirgacheffe for a bright, juicy light roast (Agtron ~65) with citrus and floral notes; their Guatemala Antigua as a balanced Full City (Agtron ~45) with chocolate and caramel; and their Sumatra Mandheling for a classic dark roast (Agtron ~35) with earthy spice and bold body. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.