Study on the Mechanism of Temperature Rise in Koji Room Fermentation based on the Influence of Microbial Metabolism

Abstract

[Objective] Koji-making rooms are the core loci of solid-state fermentation in Chinese Baijiu production; their hygrothermal state directly governs the kinetics of Daqu fermentation. Empirical retrofits based on artisanal experience no longer satisfy the stringent quality-control and intelligent-design requirements of the modern, highly engineered liquor industry. Here we elucidate the heat-rise balance mechanism that prevails during Daqu fermentation and explicitly incorporate the microbial activity-adaptation response. By quantifying the generation and transport of both heat and moisture throughout the fermentation cycle and regressing an extensive experimental dataset, we developed a steady-state hygrothermal balance model for koji-making room operation. Model predictions of spatial temperature–humidity distributions and substrate-consumption kinetics agreed with measured values within a mean relative error of <5 %, confirming high fidelity to the real system. Subsequent optimisation of ventilation/humidification schedules with the calibrated model revealed that microbial kinetics obey clear environment–activity relationships. For a small-scale koji-making room, an airflow rate of 80 m³ h^-¹ delivered in five 12-min pulses per hour maximised substrate utilisation efficiency while maintaining thermal equilibrium. These findings underscore the pivotal role of microbial activity adaptation in hygrothermal control and establish, for the first time, a mathematical characterisation of Daqu as both a moisture and a heat source. The model furnishes a quantitative platform for future simulation-based optimisation and offers a new paradigm for the intelligent design of next-generation koji-making rooms.