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First Crack vs. Second Crack: What Coffee Sounds Can Tell Us
Learn how first and second crack sound, what causes the beans to crack, and how real roast recordings and acoustic studies help explain the difference.
Quick Answer
First crack is usually a series of distinct, popcorn-like pops. Second crack comes later and tends to sound like lighter snaps arriving more rapidly. Roasters listen for the changing pattern as well as the sound of each crack.
On This Page7 Sections
What First and Second Crack Sound Like
Listen for separate pops becoming a finer, busier crackle later in the roast. The size of an individual sound and the number of sounds are different clues: a dense run of light clicks need not contain the strongest events.
For a real listening example, use Thompson Owen's first- and second-crack recordings at Sweet Maria's. The page includes a narrated air-roaster comparison and separate first-crack examples. Listen once for the individual sounds, then again for their spacing.
What Is Cracking Inside the Bean?
As beans heat, water is lost, gases form and pressure builds within a changing, expanding structure. Cracking releases some of that pressure as the structure fractures. The beans continue to dry and change after first crack; later structural fractures produce the finer snapping associated with second crack.
A roast may be finished before second crack, so both stages do not have to appear in every recording. The roaster's heat input, the beans and the recording setup all help shape what you hear.
What Acoustic Studies Add
Three measurements separate features that the ear can easily mix together:
- Amplitude is the strength of a recorded event.
- Frequency content describes how sound energy is distributed across frequencies. A crack is more complex than a single musical note.
- Event rate is the number of distinguishable events in an interval, or the pace of the chorus.
Preston Wilson's 2014 study investigated automated roast monitoring and reported these relative differences in its recordings:
Swipe to see all columnsScroll to see all columns
| Acoustic feature | First crack | Second crack |
|---|---|---|
| Amplitude of events | Greater | Lower |
| Low-frequency energy | More | Less |
| Rate of events | Lower | Higher |
In Siebald and colleagues' 2024 study, a sample drum roaster was monitored with two microphones under five starting-temperature conditions, each repeated five times. The researchers found distinguishable spectral patterns and, for most tested processes, sound-pressure patterns as bean temperature changed, and also investigated estimating the proportion of cracked beans.
The university-hosted paper reports different first-crack onset times under those conditions. It also discusses earlier research with a different first-versus-second-crack frequency pattern from Wilson's. Those details explain why a useful sound comparison keeps the roast conditions and microphone setup attached.
Compare Recordings with Their Context
Keep playback settings steady and check how the clips were made. The roasting process, microphone position and audio editing affect a comparison. Separately normalized clips can help you hear patterns, but their playback loudness cannot establish which original events were stronger.
Listen once before reading the claimed stage label, then compare your note with the supplied recording context. A spectrogram can help separate frequency patterns when its axes, units, time range and processing are clear.
Keep the audible observation beside the information that supports its interpretation.
| What I hear | Context and useful conclusion |
|---|---|
| A later passage contains more closely spaced clicks | Both passages come from one recording with unchanged gain. The audible event pattern becomes denser. |
| A second clip sounds louder | Each clip was normalized separately. Playback loudness cannot settle which original events were stronger. |
| A clip is labeled "after first crack" | No tasting or roast record is supplied. The label alone does not explain the finished cup. |
What a Crack Stage Tells You When Buying Coffee
A phrase such as "dropped after first crack" locates a point in the roaster's process. Ask what cup profile the roaster was aiming for and how the coffee tasted. The coffee roast-level guide connects roast descriptions with flavor and buying choices; the oily-beans explanation covers surface shine.
A personal note: The difference between a pop and a run of clicks makes me want to listen more closely. I would rather write “the events seem closer together here” than jump straight to a roast label. Then I want to compare that note with the recording details and the roaster’s explanation. That small separation appeals to me: listening can sharpen the question without having to supply every answer. When I am choosing coffee, I still want the conversation to come back to what is in the cup.
Sources
- Wilson, P. S. (2014). Coffee roasting acoustics. Journal of the Acoustical Society of America 135, EL265–EL269. DOI: 10.1121/1.4874355.
- Siebald, H., Möller, M., Lenz, F., Kirchner, S., and Hensel, O. (2024). Acoustic condition monitoring of coffee beans, during the roasting process. LWT 199, 116119. DOI: 10.1016/j.lwt.2024.116119.
- Siebald et al. (2024). University of Kassel repository copy of Acoustic condition monitoring of coffee beans, during the roasting process.
- Thompson Owen, First Crack FAQ: What is First Crack? What is Second Crack? Sweet Maria's, with contextual roast recordings.