What is a "crash" in roasting?
A "crash" in roasting is a sudden, undesirable drop in the Rate of Rise (ROR) curve, typically occurring shortly after the . This defect indicates that the bean’s internal energy management has failed, often leading to a "baked" flavor characterized by flat, dull, or papery taste notes because the heat could not be maintained during the final development phase.
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In professional roasting, we manage heat with extreme precision, tracking the Rate of Rise—the speed at which the bean temperature is increasing. A "crash" occurs when that ROR curve abruptly loses momentum, plummeting toward zero or even turning negative. This usually happens in the minutes following the , a period where the coffee is undergoing rapid exothermic (heat-releasing) and then endothermic (heat-absorbing) changes.
When a crash occurs, the bean essentially stops developing its complex aromatic compounds. Because the temperature isn't rising, the chemical reactions required for proper caramelization and the breakdown of chlorogenic acids stall. The result is "baked" coffee. You might recognize this in the cup: it lacks the vibrant acidity or sweet, complex fruit notes you’d expect. Instead, the flavor is muted, tasting papery, hollow, or simply "flat."
Why does a crash happen? Often, it is a failure in profile management. A roaster might have applied too much energy early on, causing the bean to reach the too quickly, leaving it without the thermal inertia to keep moving. Alternatively, it can be a failure to manage airflow correctly. During the , the bean releases a significant amount of moisture and chaff; if the roaster doesn't adjust the exhaust or heat input, the bean can effectively cool itself down too rapidly.
Preventing a crash is a hallmark of an expert roaster. It requires understanding the specific density and moisture of the to ensure the roast carries enough momentum through the development phase. By monitoring the ROR closely and making incremental, informed adjustments—rather than drastic ones—a roaster can ensure a steady, smooth decline in the ROR rather than a crash. In daily practice, avoiding this defect ensures that the hard work done by the farmers at origin is preserved rather than destroyed by a poorly controlled roast.
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