tags: [] - coffee/roasting - coffee/roasting/profile aliases: - Exothermic stage - Exothermic roasting phase

Exothermic Phase¶

Overview¶

The exothermic phase of coffee roasting is the period during which the beans release heat energy as a result of the chemical reactions occurring within them — primarily first crack, the caramelisation and late Maillard reactions of the development phase, and pyrolytic breakdown. An exothermic reaction releases energy to the surrounding environment; in coffee roasting, this means the beans themselves become a heat source during the development phase, supplementing the drum's energy input and accelerating the Rate of Rise. Managing the exothermic contribution of first crack and the development phase is one of the most technically demanding aspects of roast profile control.

Exothermic Events in Coffee Roasting¶

First crack: The most dramatic exothermic event in the roast. First crack is caused by the buildup of steam and CO₂ inside the bean reaching a pressure that fractures the cell walls. The structural fracturing is accompanied by a release of stored energy — the beans momentarily generate heat in addition to absorbing it from the drum. This exothermic pulse typically produces a spike in the Rate of Rise curve that, if the roaster has not reduced gas input beforehand, can drive the roast through the development phase more rapidly than intended.

Development phase (post-crack): After first crack, caramelisation reactions and pyrolysis continue to release energy exothermically as complex molecules break down. The exothermic character of the development phase is less dramatic than first crack itself but sustained — the beans continue to release energy throughout development, meaning that the gas input required to sustain the roast decreases relative to the endothermic drying phase.

Second crack: A second exothermic event at higher temperatures (typically 225–240 °C), caused by further structural collapse of the bean. Second crack characterises Vienna, French, and Italian roast levels.

Managing the Exothermic Phase¶

Because the beans generate heat during first crack and development, roasters must reduce gas input before these events to prevent an uncontrolled RoR spike:

Gas reduction before first crack: Reducing burner output 30–60 seconds before first crack is anticipated ensures that the exothermic energy of the crack itself does not add to an already-high gas input, preventing a steep RoR spike
Declining RoR through development: The exothermic character of development means that maintaining a constant gas input will accelerate the roast through this phase; the roaster must actively reduce gas to achieve a declining RoR
Crash avoidance: Reducing gas too aggressively in response to a first crack spike can cause the RoR to drop too sharply (a "crash"), stalling development and risking underdevelopment

Contrast With Endothermic Phase¶

Phase	Thermal character	Gas management approach
Drying phase	Endothermic; beans absorb heat	Sustained or increasing gas to maintain RoR
Browning phase	Transitioning	Gas modulated; watch for first crack approach
First crack	Exothermic pulse	Gas already reduced before crack begins
Development	Sustained exothermic	Declining gas to maintain controlled declining RoR

Key Facts¶

Exothermic phase: beans release heat energy rather than absorbing it; occurs at first crack and through development
First crack is the primary exothermic event — bean structural fracture releases stored energy, causing RoR spike
Second crack is a further exothermic event at dark roast temperatures
Development phase is sustained exothermic: caramelisation and pyrolysis release energy progressively
Gas must be reduced before first crack to prevent exothermic energy from producing uncontrolled RoR spike
Declining RoR through development requires active gas reduction against the exothermic background

References¶

Changelog¶

Date	Change
2026-04-27	Note created
2026-05-03	Compliance review: added `---` before copyright

This article is part of All-About-Coffee.com - The comprehensive coffee knowledgebase.