The transformation from green coffee beans to rich, aromatic roasted coffee is a complex and fascinating process. At Merlo, we’ve spent years refining our roasting methods to deliver exceptional flavour in every cup. In this guide, we’ll walk you through each stage of the roast from pale green beans to perfectly roasted coffee.

From Green to Roasted: The Coffee Bean Journey

Warm-Up Phase

The roast begins with green beans gradually heating. Drum roasters take longer to warm up, while hot air roasters (like Merlo’s) transfer heat more efficiently, speeding up the process. The beans begin to pale and prepare for transformation.

Yellow Stage

As the beans lose moisture, they emit a light, grassy aroma. The surface begins to yellow, and the coffee starts taking on heat, setting the stage for further colour and flavour development.

Yellow-Tan Stage

Beans start shifting from yellow to tan, and marbled patterns begin to appear. A gentle toasted aroma emerges, a sign the roast is progressing steadily.

Browning & Expansion

As colour deepens, beans begin to expand. The central crack opens slightly and releases silverskin or chaff. This stage signals the approach of the first crack.

The First Crack: Where Coffee Comes Alive

Audible Change

The first crack sounds like popcorn popping - an exothermic reaction where the beans release heat and expand rapidly. Colour may look mottled, but this is part of the transition to a fully developed roast.

Managing Heat

It’s critical to maintain consistent, high heat during this stage. If the roast stalls, the result will be a flat, “baked” flavour instead of a vibrant, complex cup.

End of First Crack

When beans develop a smoother texture and fine line patterns, the first crack has finished. At this stage, you can stop the roast for a light roast or continue for deeper flavour profiles.

Coffee Roast Levels Explained

The point at which you stop the roast determines the flavour, aroma, and character of the coffee. From light to dark, each level has a distinct personality.

Light Plus Roast

Just beyond the first crack, beans take on a soft surface and balanced acidity. Original bean characteristics remain, with added complexity and a slight boost in body.

Medium Roast

Beans are removed just before the second crack begins. This roast balances origin flavours with caramel, chocolate, and toast notes - ideal for those who enjoy well-rounded coffee.

Medium Plus Roast

Stopped at the start of the second crack, this roast offers rich, full-bodied flavour with enhanced sweetness and subtle bitterness. It’s bold but still balanced.

Medium to Dark Roast

Roasted just beyond the second crack, this level brings strong roast character, reduced acidity, and a full-bodied finish. It’s where most Merlo blends are roasted to ensure great flavour and long shelf life.

Full Dark Roast

Beyond this stage, beans begin to carbonise. Even a few seconds too long will result in burnt, ashy flavours, a reminder that timing is everything in roasting.

Experience Merlo’s Expert Roasting

Every step in the roasting process impacts your final cup, from aroma and body to sweetness and finish. At Merlo, our expert roasters use hot air bed roasting to ensure clean, consistent results without scorching.

Visit one of our roasting houses to experience the roasting process in action and discover what goes into every freshly brewed Merlo coffee.