Gibbs free energy (ΔG)
Gibbs free energy
Japanese: ギブスの自由エネルギー（ΔG）
A thermodynamic indicator of whether a reaction proceeds spontaneously. Negative ΔG means spontaneous; positive ΔG requires external energy.
Gibbs free energy (G) is a thermodynamic state function indicating whether a system has the capacity to do work. If the change in free energy (ΔG) between reactants and products is negative, the reaction proceeds spontaneously; if positive, it does not.
Alcoholic fermentation has ΔG = -235 kJ/mol per mole of glucose—a large negative value meaning it readily proceeds. Yeast captures part of this energy as ATP; the rest dissipates as heat.
Miso fermentation tanks becoming slightly warm is due to this dissipated thermal energy. Feeling the spontaneity of invisible chemical reactions through your palm—fermentation is a rare phenomenon where thermodynamics becomes tangible.