How chemical equilibrium influences pungency evolution: Evidence from aged Baijiu

Balance deviation quantifies the acid–ester equilibrium state. • Balance deviation shows a V-shaped link to pungency. • This framework converts empirical ageing rules into thermodynamic terms. This study demonstrates that the pungency of Chinese Baijiu is governed by the thermodynamic equilibrium of its main acid–ester pairs. During distillation, a non-equilibrium state with high ester and low acid levels forms, which then moves towards equilibrium during ageing. We quantify this process using the balance deviation (BD, defined as the ratio of the reaction quotient to the equilibrium constant). Results reveal that pungency decreases as BD approaches 1, whereas deviations in either direction increase pungency, creating a V-shaped trend. Additionally, surpassing a critical total concentration threshold elevates pungency even at equilibrium. Overall, this research shifts the empirical rule of ‘acid increase, ester decrease’ into a quantitative thermodynamic model, offering a general framework for understanding how chemical equilibrium influences sensory perception.