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  • #16
    Originally posted by triton91 View Post
    "coasting" is when the beans losing heat.

    This is why
    "First crack is an exothermic reaction; the beans are giving off heat. But then the beans quickly become endothermic, meaning that a roaster that is not adding enough heat to the process will stall the roast at this point ...not a good thing. Once caramelization begins (340-400 f degrees internal bean temperature) a roast that looses heat will taste "baked", perhaps due to the disruption on long-chain polymerization. The melting point of sucrose is 370 f and corresponds to this window of temperatures when caramelization begins."
    This explanation for "coasting" doesn't really make sense. Heat and temperature are not the same thing.

    The beans can only lose heat if they are at a higher temperature than their surroundings - regardless of whether or not the *reactions* are endo or exothermic.

    If a *reaction* is endothermic, it means the reaction products have higher chemical energy than the reagents.

    In an isolated system (where no heat can transfer in/out), this will result in a decrease in the temperature until such time that the reaction stops because it is no longer kinetically favourable. The system is not losing energy (i.e. heat), it's merely being converted to chemical bonds!

    In an open system, if the surroundings are at a greater temperature than the reacting system, then there will be a net transfer of heat (i.e. energy) from the surroundings TO the system, lowering the temperature of the surroundings until such time as they reach temperature equilibrium with the system.

    In a roaster, you can maintain the temperature of the surroundings (i.e. the air and the roaster) provided your heat input (to the air/roaster) matches the rate of heat transfer from the air/roaster to the beans.

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    • #17
      hmmmm .... a simple explanation/driving analogy I think would amount to taking your foot off the accelerator and letting time and distance decrease speed naturally, neither braking nor accelerating aka coasting. No cruise control option ... lol

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