First crack
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German: First Crack (erstes Knacken) Also known as: Erstes Knacken, Second Crack
The audible cracking of beans during roasting that marks the transition to a drinkable roast.
During roasting, pressure inside the bean rises through steam and gases. At a certain temperature the beans burst open with an audible crack, the first crack. From this point the coffee is basically drinkable and the beans expand noticeably.
Light roasts are ended shortly after or around the first crack. If a second, quieter cracking sets in later (second crack), the dark range begins, in which oils can reach the surface. Roasters use these signals as orientation during the roast.