Light Roast vs Dark Roast: What Actually Changes in the Cup

The most common question about coffee roast levels is about caffeine: does darker mean stronger? The answer is no — and understanding why reveals how roasting actually works.

What Roasting Actually Does to a Coffee Bean

Green coffee beans are essentially seeds — dense, grassy-smelling, and almost unrecognisable as coffee. Roasting applies heat that triggers a series of chemical reactions. The Maillard reaction begins at approximately 150°C, creating roasty, caramel, and nutty notes. First crack occurs at approximately 196°C — this is when light roasts are typically finished. Second crack occurs at approximately 224°C, where dark roasts are taken.

The Caffeine Question

The persistent belief that darker roasts contain more caffeine is a myth. Caffeine is a stable molecule that does not degrade significantly at roasting temperatures. By weight, light and dark roast contain almost exactly the same amount of caffeine per gram.

Acidity: Why It's Higher in Light Roast

Light roast retains a higher proportion of chlorogenic acids, contributing to bright, clean acidity. As roasting continues, chlorogenic acids break down into quinic acid — which is bitter rather than bright.

Flavour: Origin Character vs Roast Character

Light roast preserves origin character — the flavours that distinguish an Ethiopian Yirgacheffe from a Colombian Huila. Dark roast creates roast character — past second crack, most volatile aromatic compounds have burned off, leaving the flavour of roasting itself.

Body and Brewing

Dark roast tends to produce a heavier body; light roast is lighter and more transparent. Pour over suits light to medium roasts. French press and cold brew suit medium to dark. Espresso works across the spectrum but light roast requires more precise technique.

Summary: When to Choose Each

Choose light roast when you want to taste origin character, prefer brightness and floral notes, or are brewing pour over. Choose dark roast when you want bold consistent flavour, are adding milk, or making cold brew. Medium roast is often the most versatile option.