Coffee Roasting: First Crack vs. Second Crack

Roasting coffee beans is essentially the process of applying heat to green coffee beans, which initially exhibit only faint grassy and subtle fruity aromas, and virtually no taste. The roasting process triggers a series of chemical reactions within the beans, releasing the flavors previously locked inside the green coffee. Anyone familiar with coffee roasting will likely have encountered terms such as "first crack" and "second crack." But what exactly are these cracks, and how do they differ?

What Is the First Crack?

The first crack occurs due to heat-induced pressure from large amounts of gas and steam formed inside the coffee beans. When internal pressure becomes too great, the beans expand, resulting in an audible cracking sound. Typically, this first crack happens at roasting temperatures between 180–205°C. The sound is relatively loud and resembles popping popcorn.

What Is the Second Crack?

If roasting continues beyond the first crack, you'll eventually hear a softer, subtler sound—this is the second crack, occurring at temperatures around 205–230°C. During the second crack, roasters must closely monitor the beans and decide decisively when to end roasting, as even a few extra seconds can drastically alter flavor profiles. After second crack, substantial oils under pressure migrate from inside the beans to the surface, making them appear glossy. Beans roasted past second crack develop a pronounced bitterness, very low acidity, and a notable smoky character.

Identifying and Controlling the First Crack

The onset of first crack is a critical control point during roasting. Flavor development accelerates rapidly from this moment, though not all beans crack simultaneously. Typically, you'll first hear scattered cracks, followed by short silence, then additional cracks. At a certain point, it seems as though one bean triggers a chain reaction, resulting in continuous crackling sounds.

Variability of First Crack Sounds

The audibility of the first crack can vary significantly depending on the beans. Some beans have very distinct and clear cracking sounds, while others produce weaker, less noticeable cracks. Beans from lower elevations or with lower density often produce faint cracking sounds.

What If the First Crack is Hard to Hear?

Occasionally, the roasting machine’s insulation or structure can muffle sounds, making it difficult to hear the cracks clearly. In such cases, roasters must rely on other sensory indicators:

1. Smell: Use a sampling spoon to smell the beans. At the onset of first crack, the beans emit a distinctly vinegary aroma.
2. Visual Inspection: Observing beans with a sampling spoon can help. Beans actively cracking will visibly bounce or jump slightly, confirming the roasting stage.

By leveraging these multiple sensory inputs, roasters can maintain precise control and consistency, even when auditory cues are limited.