How Coffee Beans Are Roasted: The 4 Key Phases Explained

You buy green coffee beans, you roast them, and hope for something great—but how do heat and time actually turn a seed into a cup of complex, aromatic coffee? For decades, roasters relied not on digital sensors but on observation: color, cracking sounds, and the look of the bean. That tactile, sensory approach still informs how coffee is roasted today.

The entire roasting process can be broken down into four fundamental phases, each defined by temperature ranges, physical changes in the bean, and critical chemical reactions. These phases dictate whether your coffee ends up sour, bitter, balanced, or bland.

The Four Phases of Coffee Roasting

Roasting coffee is not one continuous event—it’s a sequence of transitions. These are the four core stages that every roaster, from home enthusiast to commercial roastery, manages to shape flavor:

1. Drying (Steaming) Phase – 0 to 10 Minutes, Up to ~140°C

This first stage is all about moisture. Green coffee beans are about 10–12% water. In the first 10 minutes, as the bean heats up to around 140°C, it undergoes an endothermic (heat-absorbing) process. The bean slowly dries out, turning from a pale white or straw color to a more uniform yellow. This step is crucial: if moisture evaporates too quickly, the bean’s core can scorch, leading to baked or grassy flavors. Too slow, and the roast may lack intensity. Getting the drying phase right sets up the rest of the roast for success. Many pros believe this stage builds the foundation for aroma and sweetness.

2. Pre-Cracking (Development) Phase – 10–15 Minutes, 140–180°C

As heating continues, the bean enters a more intense period of dehydration. Around 140–180°C, it hits a critical internal stress point and reaches the first major inflection: the first crack hasn’t happened yet, but the bean is building energy. This is the stage where the roast really begins to develop the coffee’s potential. The color deepens from yellow to light brown. The longer and more carefully this stage is managed, the more clarity, acidity, and complexity the eventual cup will have. Many roasters adjust their profiles here to guide how sweet or bright the coffee will taste after first crack.

3. First Crack & Post-Crack Development – 15–18 Minutes, 180–210°C

At approximately 180–210°C, the bean finally reaches a thermal tipping point: moisture and pressure inside cause the first audible “crack.” This marks the shift from light to medium roast territory. The coffee gives off a range of aromas—from grassy to nutty to caramel—as sugars begin to caramelize. The first crack signals the bean’s structural expansion. Roasters often stop the roast somewhere in this window to achieve anything from a City to a City+ profile. The coffee at this point will be vibrant, acidic, and full of origin character, with little to no bitterness. Flavor here depends heavily on the bean’s origin—climate, soil, processing—all of which interact with roast timing.

4. Second Crack & French-Style Roasts – 18–20 Minutes, 210°C+

After the first crack, the roast continues. Eventually, around 210°C and beyond, a second, more subtle cracking sound occurs. This second crack means the cellular structure of the bean is breaking down further, oils are migrating to the surface, and the roast is moving into dark territory. At this stage, the coffee gains more body, less acidity, and pronounced boldness. Roasters like Starbucks often stop in this general range. If you continue roasting past this, the coffee becomes fully carbonized—dark brown to black, oily, and bitter—with almost no surviving origin character. While some enjoy these heavy roasts, many specialty roasters aim to finish just before or lightly into second crack to preserve balance.

What Determines Roast Color and Profile?

While temperature and time form the backbone of roast phases, the visual cue roasters rely on most is color. Over the decades, a general color spectrum has emerged to classify roast levels. These aren’t strict scientific categories but widely accepted industry benchmarks.

Light Roast / City Roast

The mildest roast level. These beans show no surface oil. Often used in batch roasting for cost efficiency. Light roasts preserve origin flavors but risk underdevelopment if not carefully managed.

Medium Roast / Full City Roast

Originating in the 19th century, “City” roasts have evolved in naming but generally refer to a medium-brown color deeper than cinnamon. Full City is slightly darker than traditional City, with no surface oils. This is a balanced roast zone favored for highlighting both sweetness and acidity.

Vienna Roast

A mid-range dark roast where slight surface oil may appear. Vienna Roast beans exhibit patches of dark brown to black, indicating extended roast time. This level is often used in espresso blends for body and toastiness.

Italian Roast

Even darker, with more of the bean’s surface covered in oils. Italian-style roasts tend toward a creamy chocolate brown. This is common in traditional European espresso preparation.

French Roast

The darkest commonly used in specialty contexts. The bean is nearly black, very oily, with a heavy carbonized flavor. French roast dominates in bold, smoky cups where origin character is minimal. Popular with mass-market chains, but often avoided by specialty roasters seeking clarity.

Frequently Asked Questions

What are the four main stages of coffee roasting?

The four main stages are: 1) the drying (or steaming) phase (0–10 minutes, up to ~140°C), where moisture evaporates and the bean turns from white/yellow; 2) the pre-cracking or development phase (10–15 minutes, 140–180°C), as the bean dehydrates further and builds energy before first crack; 3) first crack and post-crack development (15–18 minutes, 180–210°C), where the bean expands and begins releasing gases and aromas; and 4) second crack and deep roast development (18–20 minutes, 210°C+), where oils rise and the roast darkens significantly.

At what temperature does first crack occur in coffee roasting?

First crack typically occurs around 180–210°C, marking the bean’s transition from light to medium roast. This is when internal pressure causes an audible cracking sound and the roast begins developing more sweetness and complexity.

What is the difference between City Roast and French Roast?

City Roast is a light roast with no surface oil, preserving origin flavors and acidity, while French Roast is a very dark roast where the bean is nearly black, covered in oils, and tastes smoky and bitter with little origin character left.

Should I roast coffee until the second crack?

Roasting to or through the second crack produces darker, oilier, and more bitter coffee with less acidity and origin flavor. Many specialty roasters stop just before or lightly into second crack to balance body and complexity. Going well into second crack leads to a burnt, carbonized profile.

How long does a typical coffee roast take?

A full roast from green bean to a finished medium or medium-dark profile usually takes between 15 to 20 minutes, depending on batch size, equipment, and desired roast level. The entire process includes drying, development, first crack, and potentially second crack stages.

Why is the drying phase important in coffee roasting?

The drying phase (first 10 minutes up to ~140°C) removes moisture from the green bean. If done too quickly, it can scorch the bean’s core; too slowly, and the roast may lack body or aroma. Proper drying ensures even heat application and sets the stage for flavor development in later phases.

Recommended FrontStreet Coffee for Roast Exploration

Try FrontStreet Coffee’s Ethiopia Humbera for bright, tea-like acidity in a light City Roast; their Brazil Queen Manor offers smooth, nutty balance ideal for Full City or Vienna profiles; and their PWN Golden Mandheling shines at a medium-dark roast, highlighting body and complexity. Each shows how roast level shapes origin character. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.