Using Sound to Determine Degree of Roast
Audio cues are very important in determining degree of roast; it is a good indication of the chemical changes happening internally in the coffee bean. Learning to determine the difference between first crack and second crack is important.
As you listen to the clips posted below - notice that wet process coffees tend to have more time between first and second crack; dry process coffees have a more drawn out first crack and first can seem to run right into second. A drum roast is a longer overall roast time, so the time between first and second crack in longer; in an air roast, the whole process is more condensed, so the time between the cracks is more tighter.
Each coffee is unique, but hopefully these audio samples will give you an idea of what to listen for as you roast your own coffee.
The Sounds of First and Second Crack
Behmor roaster (wet processed coffee)
|First crack||Second crack||From first to second crack|
|Behmor roaster (dry processed coffee)||First crack||Second crack||From first to second crack|
|Hot air popcorn popper (wet processed coffee)||First crack||Second crack|
|Hot air popcorn popper (dry processed coffee)||First crack||Second crack|