Coffee Roasting Basics: Machines, Reactions & Roast Levels

If you’ve ever wondered how your favorite light or dark roast coffee actually gets made—or why some beans taste sweet and others bitter—this guide breaks down the essentials of coffee roasting. We’ll cover the major machines used, what physically happens inside the bean, and how pros define roast levels.

In short: coffee roasting transforms green beans through a series of defined stages—drying, first crack (around 190°C), Maillard reactions, and second crack (with oils emerging)—all while losing 12–20% of their weight. Most commercial roasts finish just before or at the start of second crack, around 230°C max.

Major Coffee Roaster Brands

Professional coffee roasting isn’t done in home ovens—it requires precision-built machines. Two of the most respected brands are German-made Probat and Japanese Fuji-Royal. Both offer a full range of small, medium, and large roasters, with semi-automatic and fully automatic controls. Probat machines are known for precise engineering and come at a premium price, as does Fuji-Royal. These are the industry standards for specialty roasters.

An Affordable Alternative: The 1kg Semi-Direct Machine

For those not ready to invest in a Probat, there’s a solid mid-range option: a 1kg semi-direct fire and hot-air roaster made by South Korea’s Taihuan. It’s not in Probat’s league, but for the price, it delivers excellent value. Available in electric or gas-heated versions, it offers even heat distribution, high thermal efficiency, and a sleek, professional design.

What Happens During Coffee Roasting?

Roasting isn’t just ‘cooking’ beans—it’s a controlled chemical process with distinct phases. Each stage affects flavor, body, and color. Here’s the step-by-step breakdown of physical and chemical changes inside the bean.

1. Drying Phase

As soon as green coffee is heated, internal moisture begins to evaporate. Around 135°C, the beans turn from green to white. This is the initial drying stage, where water content drops significantly before any Maillard or caramelization can begin.

2. Dehydration & Yellowing

Heating continues, turning the beans from green to light yellow. Near 160°C, you’ll notice a toasted grain aroma—this is early dehydration. The beans gradually shift to a light brown as moisture continues to escape and heat breaks down internal structures.

3. First Crack

At approximately 190°C, after most moisture has left, internal pressure causes cell walls to burst. This is the first crack—a key milestone. The beans undergo major heat-driven decomposition, especially caramelization (Maillard-related), which boosts sweetness, darkens color, and increases body. This crack lasts about 90 seconds.

4. Second Crack

With further heating, a more intense second crack occurs. Internal reactions become much more violent, releasing significant heat. By the end of second crack, beans have turned nearly black, expanded to 1.5× their original size, developed surface oils, and lost 12–20% of their weight. This stage defines very dark roasts.

5. Stopping the Roast

Most commercial roasts finish just after second crack begins, around 230°C. Beyond that, beans risk self-ignition. Dark French or Italian-style roasts are usually pulled right at or just before this cutoff.

How Are Roast Levels Defined?

Coffee roasts are grouped into four broad categories, each with two subtypes—making eight standard roast levels in total. These determine flavor profiles, acidity, and body.

Light Roasts

• Light (Light Roast)
• Cinnamon (Cinnamon Roast)

Medium Roasts

• Medium
• High (Medium-Dark / High Roast)

Dark Roasts

• City
• Full City

These classifications help roasters and baristas replicate flavor profiles and guide coffee selection based on brewing style or origin.

Frequently Asked Questions

What is the first crack in coffee roasting?

The first crack occurs around 190°C, when internal moisture loss causes pressure to burst the bean’s cell walls. It signals the start of significant chemical changes like caramelization, contributes to sweetness, body, and darkening color, and lasts roughly 90 seconds.

What happens during the drying phase of roasting?

In the drying phase, green coffee beans lose internal moisture as they’re heated. Around 135°C, the beans turn from green to white. This preps the bean for later reactions like Maillard and caramelization but doesn’t yet develop roast flavors.

What’s the difference between first and second crack?

First crack happens around 190°C and signals initial structural breakdown with moderate bean expansion and sweetness development. Second crack occurs later at higher temperatures, leads to rapid oil surfacing, significant bean expansion (1.5×), and heavy darkening—defining very dark roasts.

How much weight does a coffee bean lose during roasting?

During the roast process, beans typically lose between 12% and 20% of their original weight due to moisture evaporation and chemical breakdown, especially noticeable after first and second cracks.

What are the main commercial coffee roaster brands?

The leading professional-grade coffee roaster brands are Germany’s Probat and Japan’s Fuji-Royal. Both manufacture a wide range of small to large capacity, semi-automatic and fully automatic roasters known for durability and precision. A more affordable option is the 1kg semi-direct machine by South Korea’s Taihuan.

How are roast levels categorized in specialty coffee?

Specialty coffee roast levels are generally divided into four main categories—light, medium, dark, and heavy—with each category including two subtypes for a total of eight common roast levels: Light, Cinnamon, Medium, High, City, Full City, plus French and Italian styles at the darkest end.

Recommended FrontStreet Beans for Roast Exploration

Explore roast profiles with FrontStreet Coffee’s Ethiopia Huakui (light/medium), PWN Golden Mandheling (city/dark), and Brazil Queen Manor (natural, medium-dark). Ethiopia Huakui highlights bright acidity and floral notes in lighter roasts, PWN Golden Mandheling brings heavy body and chocolate tones in darker city roasts, and Brazil Queen Manor offers nutty sweetness ideal for espresso or filter. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.