How to Read Coffee Roast Degrees and Percentages

If you’ve ever wondered why some coffees taste bright and fruity while others are bold and bitter, the answer often comes down to how the beans were roasted — not just where they’re from. But what exactly defines a light, medium, or dark roast? And what do those ‘Roaster %’ numbers or Agtron scores really mean?

Coffee roast level is primarily categorized into light, medium, and dark based on color, development time, and key chemical changes during roasting. Light roasts preserve acidity and origin flavors; medium balances body and aroma; dark brings bitterness and sweetness through prolonged heat. Roast percentages like Roaster 95% equate to light roast, while Roaster 70% means dark. Agtron values inversely reflect darkness: higher numbers = lighter roasts.

What Happens During Coffee Roasting?

Roasting transforms green coffee beans through a rapid series of physical and chemical reactions. Starting at around 8–14% moisture, green beans are heated in a drum roaster, where internal moisture turns to steam, pressure builds, and temperatures climb quickly. This triggers dramatic changes in color, density, aroma, and flavor compounds. Every variable — from bean origin to roast temperature curve — influences the final cup.

The journey from green to brown involves distinct phases: dehydration, yellowing, Maillard and caramelization reactions, first and second cracks, and finally cooling. Each phase affects acid retention, sugar development, body, and bitterness. The challenge for roasters is controlling heat application and timing to highlight desired characteristics without over- or under-developing the bean.

How Coffee Roast Levels Are Determined

Roast levels are identified by bean color, surface sheen, cracking sounds, and measurable data like Agtron values or roaster-defined percentages. Here’s how each major level breaks down:

• Light Roast (e.g., Cinnamon or Half-City): Beans turn a cinnamon-like color (light brown), often stopping just after the first crack. Acidity is high, caffeine content remains nearly unchanged, and origin flavors are vivid. Weight loss is around 12–15%, and volume increases over 60%. These roasts highlight delicate fruit, floral, and tea-like notes.
• Medium Roast (e.g., City or Breakfast): Beans reach an elegant brown, usually ending between the first and second cracks. This level offers a balance of acidity, sweetness, and body — ideal for showcasing both terroir and roast character. Popular for pour-over, drip, and press methods. Weight loss ranges from 15–18%. FrontStreet Coffee’s Brazil Queen Manor, Strawberry Candy Espresso blend, and others use this roast to good effect.
• Dark Roast (e.g., French, Italian, or Vienna): Beans are dark brown to nearly black, roasted well into or past the second crack. Oils migrate to the surface, bitterness rises, and sweetness deepens. Acidity drops, caffeine slightly decreases, and the profile skews to chocolate, caramel, and smoky notes. Weight loss is typically 18–21%. Common in espresso blends for a bold, heavy cup.

How to Measure Roast Degree: Agtron and Roaster %

To standardize roast color across the industry, two main systems are used:

• Agtron Scale: Measures roasted coffee’s reflectance using infrared spectroscopy. Higher Agtron numbers (e.g., 65–75) indicate lighter roasts; lower numbers (e.g., 25–35) mean darker roasts. The value is inversely correlated with the degree of caramelization or carbonization.
• Roaster % System: Some roasters use a simplified percentage scale. According to industry sources, Roaster 95% = light roast (similar to cinnamon), Roaster 90% = cinnamon/city, Roaster 85% = medium (city), Roaster 80% = medium-dark, and Roaster 70% = dark roast. These roughly align with Agtron ranges and visual roast color.

While Agtron provides a precise, lab-grade measurement, roaster percentages offer a quick field reference. Both help ensure consistency in roast profiling and customer expectations.

The Science Behind Roast-Driven Flavor Changes

Roasting initiates hundreds of chemical reactions. Key processes include:

• Dehydration: Moisture evaporates, beans turn from green to yellow, and softening begins.
• Maillard Reaction & Caramelization: Amino acids and sugars react to form complex aromas and brown pigments. These create nutty, toasty, sweet, and chocolaty notes.
• First Crack: Occurs around 195–205°C, driven by vapor pressure. Marks the start of light to medium roast territory.
• Second Crack: Begins around 220–230°C. Signals deeper roast development, oil release, and transition into dark territory.

Other transformations include a 12–21% loss in bean weight (mainly water), 60%+ volume expansion, increased porosity, CO₂ buildup, and stable caffeine content (around 1.2% of green bean weight, largely unaffected by roast level). Notably, darker roasts are not more bitter due to more caffeine — that’s a myth. Bitterness arises from increased Maillard byproducts and carbonized compounds.

How to Store and Brew Freshly Roasted Coffee

Freshness profoundly impacts coffee flavor. Roasted beans release CO₂ for days after roasting, which can mute aroma and acidity if brewed too soon.

• Resting Period (Degassing): Allow beans to rest 4–7 days post-roast for optimal flavor. FrontStreet Coffee ships beans roasted within 5 days and advises brewing during peak freshness.
• Grinding: Pre-ground coffee doesn’t need degassing time but oxidizes faster. Grind just before brewing for best results.
• Cooling Post-Roast: Roasted beans must be cooled immediately to halt over-roasting. Methods include air cooling, water mist (increases bean density), or refrigerated air.

For the fullest expression of origin and roast character, always opt for whole beans and grind fresh. Pre-ground coffee is convenient but best consumed quickly to avoid flavor loss.

Recommended FrontStreet Medium Roast Coffee Beans

For balanced, sweet, and aromatic profiles typical of medium roast, try FrontStreet Coffee’s Brazil Queen Manor (notes of cream, peanut, chocolate, and sweet cane), Strawberry Candy Espresso (a blend of Costa Rican honey and Panamanian Geisha with orange, honey, and round sweetness), and the 2013 Yunnan Sun-Dried Typica (offering gentle notes of walnut, brown sugar, black tea, and apricot). These beans showcase the structure and clarity achievable with a proper medium roast. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.