Roast Levels

Roasting is a transformation process. Green coffee beans contain sugars, amino acids, organic acids, lipids, and hundreds of other compounds, but they taste grassy, raw, and nothing like brewed coffee. In the roaster, temperatures reaching 195–230°C drive a cascade of chemical reactions that create the characteristic colour, aroma, and flavour of roasted coffee. The roast level determines which reactions dominate and which compounds survive.

The Chemistry of Roasting

Drying phase (100–150°C): Free moisture inside the green bean evaporates. The bean turns from green to yellow. Grassy, hay-like aromatics are prominent.

Maillard reaction (150–200°C): The defining reaction of roasting. Amino acids and reducing sugars react to produce hundreds of new flavour and aroma compounds — the brown colour, the complex aromas, the characteristic coffee smell. Nearly every pleasant aroma in roasted coffee originates in the Maillard reaction. It begins around 150°C and accelerates as temperature rises.

First crack (195–205°C): Internal steam pressure builds until the bean structure fractures with an audible crack — similar in sound to popcorn. The cell walls rupture, expanding the bean significantly. Most roasts finish somewhere after first crack; the exact timing defines the roast level.

Caramelisation (200°C+): Sugars break down and reform into hundreds of caramel compounds. This drives the development of sweetness and body beyond first crack.

Second crack (225–230°C): A second structural breakdown as CO2 and volatile compounds vent rapidly. Beans become oily on the surface (cell structure breaks down enough for oils to migrate outward). Flavour shifts strongly toward roast character rather than origin character. Beyond second crack, roasted flavours become increasingly dominant and the bean begins to ash.

Light Roast

Light roast coffee is taken to just after first crack, typically at an internal bean temperature of 195–210°C. The bean retains much of its original cellular structure; oils remain inside the bean; the bean colour is light brown.

Flavour: Origin-driven. The terroir of the coffee — the variety, the region, the processing method — is maximally expressed. Bright acidity, floral aromatics, and fruit notes are prominent. Maillard reaction compounds are present but have not been cooked further into darker, more uniform roast flavours.

Caffeine: Slightly higher than darker roasts. Caffeine is relatively heat-stable but does degrade slightly at extended high temperatures; dark roasting destroys marginally more caffeine than light roasting.

Common misconceptions: Light roast coffee is often described as "less strong." This depends entirely on what you mean by strong. Light roast has more caffeine per gram, higher acidity, and more complex flavour. It has less roast bitterness. Brewed to the same ratio, a light roast is not "weaker" — it tastes different.

Medium Roast

Medium roast typically runs from shortly after first crack to the beginning of second crack, at 210–220°C. A balance point between origin character and roast character.

Flavour: Caramel, chocolate, and nut notes emerge from deeper caramelisation. Acidity softens but remains present. Sweetness is typically at its peak — the sugars have caramelised but not yet degraded. The origin character is still present but less prominent than in light roast.

Common use: Medium roast is the most commercially successful roast level because it appeals to the widest range of drinkers. It works well in pour-over, French press, espresso, and batch brew.

Dark Roast

Dark roast pushes into and past second crack, at 220–235°C. The bean is dark brown to nearly black; oil is visible on the surface; cellular structure is substantially degraded.

Flavour: Roast character dominates. Bitter compounds produced by the Maillard reaction and caramelisation are present in high concentration. Sweetness declines as sugars degrade. Organic acids largely break down, producing a low-acidity cup. Origin character is largely or completely obscured by roast character. Common descriptors: dark chocolate, tobacco, ash, smoke.

Common use: Espresso blends historically used dark roasts because the bitterness balances milk; dark roast extracts differently at espresso pressure; and the oils on the surface of dark-roasted beans contribute to a thick, creamy espresso texture. Specialty coffee has moved strongly toward lighter espresso roasts in recent years, though dark-roast espresso remains dominant in Italian tradition.

Development Time Ratio (DTR)

Within any roast level, the development time ratio matters. DTR is the proportion of total roast time spent after first crack. A roast of 10 minutes total with 90 seconds of post-crack development has a DTR of 15%. Short DTR produces underdeveloped coffee: bready, astringent, and hollow. Long DTR at the same first-crack point produces over-developed coffee: flat, baked, muted. Most specialty roasters target 20–25% DTR for light to medium roasts, adjusting for the specific bean's density, moisture, and target profile.

Roast and Grind

Roast level affects how coffee should be ground. Dark-roasted beans are more brittle and grind more easily; they also degas CO2 more rapidly and go stale faster. Light-roasted beans are denser and require more grinder force; they retain freshness and CO2 longer, often requiring 2–5 days of rest after roasting before brewing to allow initial intense degassing to subside.