Endothermic vs Exothermic Phases
Endothermic vs. exothermic phases describe the two primary thermal states during coffee roasting: the endothermic phase, where beans absorb heat, and the exothermic phase, where beans release energy during chemical reactions.
Understanding the endothermic vs. exothermic phases is essential for mastering the thermodynamics of coffee roasting. A roast is not a linear application of heat; it is a dynamic process where the coffee bean itself begins to generate energy, fundamentally changing how the roaster must manage the heat source.
The roast begins in an endothermic phase. During this time, the beans are absorbing energy from the roasting environment to drive off moisture and initiate the early chemical reactions. Because the beans are consuming heat, the roaster must provide a steady, controlled supply of energy to keep the roast moving forward. If the heat is insufficient, the roast will stall, leading to underdeveloped, 'baked' coffee.
As the roast progresses, typically approaching the first crack, the beans reach a point where the internal chemical reactions—specifically the Maillard reaction and the breakdown of complex sugars—become exothermic. This means the beans are now releasing their own heat. This transition is a critical moment for the roaster. If the heat input is not adjusted, the temperature can spike uncontrollably, leading to a 'flick' in the rate of rise and potentially scorching the beans.
Why does this matter? Managing the transition from endothermic to exothermic is the key to roast consistency. A roaster who fails to anticipate the exothermic phase will often find their roast 'running away' from them, resulting in a roast that is darker or more developed than intended. By reducing the heat input just before the exothermic peak, the roaster can maintain a smooth, controlled rate of rise, ensuring that the development phase is even and predictable.
In practice, this means that roasting is a constant balancing act. The roaster must be sensitive to the feedback from the bean thermocouple and the roast profile software to identify the exact moment the beans begin to generate their own heat. Mastering this transition allows the roaster to produce coffee that is consistently sweet, balanced, and free from the harsh, burnt notes that occur when the exothermic phase is left unmanaged.
- · https://softschools.com/difference/endothermic_vs_exothermic/442
- · https://achillescoffeeroasters.com/blogs/specialty-coffee-blog/how-roasting-transforms-coffee-a-chemical-breakdown