# Turning-Modulated Vertical CO2 Gradients Drive Microbial Stratification and Amadori Product Accumulation in Winter Daqu

## TL;DR

This study shows how CO2 levels in winter Daqu fermentation affect microbial activity and product quality in Chinese baijiu production.

## Contribution

The study introduces a closed-loop system linking microenvironmental factors, microbiome, and metabolome to explain HTD quality variations.

## Key findings

- CO2 concentration is the core factor causing quality variations in winter Daqu fermentation.
- Vertical CO2 gradients restrict the enrichment of aerobic microbes like Bacillus species.
- Amadori product accumulation indicates stalled Maillard reactions under CO2 stress.

## Abstract

High-temperature Daqu (HTD)’s quality determines the characteristics and yield of the Chinese sauce-aroma baijiu. However, winter production frequently encounters challenges such as fermentation instability and metabolic fluctuations, primarily stemming from complex, unmonitored microenvironmental changes within the HTD pile. This study established a closed-loop system linking the microenvironment, HTD quality, microbiome, and metabolome. Through continuous monitoring of the winter fermentation pile’s microenvironmental conditions and integrating multi-omics analyses, we revealed that CO2 concentration within fermentation piles is the core factor causing quality variations in HTD. By breaking the respiratory bottleneck formed by carbon dioxide (CO2) accumulation through the turning anaerobic stress can be alleviated, thereby driving metabolic succession. The study found that vertical CO2 concentration heterogeneity severely restricts the enrichment of aerobic core functional microbial communities such as the Bacillus species. This directly blocks key metabolic pathways including amino acid metabolism and energy supply via ABC transporters. Moreover, the specific accumulation of Amadori products further confirms that this low-temperature environment under CO2 stress causes the Maillard reaction to stall at intermediate stages. Consequently, this study proposes a steady-state control strategy centered on oxygen and CO2 gas characteristics. By actively regulating the gaseous microenvironment to eliminate metabolic heterogeneity, it provides theoretical support for standardizing traditional fermentation processes.