The closed solid-state vinegar brewing system has revolutionized traditional vinegar production by introducing standardized fermentation protocols, resulting in consistent and high-quality flavor profiles. However, the intricate mechanisms governing microbial succession during the acetic acid fermentation phase within this system remain elusive. Similarly, the complex interplay between flavor components and key microbial communities is not fully understood. In this study, advanced metabolomic analysis was employed, leading to the identification and characterization of a comprehensive array of 9 organic acids, 16 free amino acids, and 64 volatile flavor substances. Metatranscriptome analysis further elucidated the dynamic shifts in microbial communities across distinct fermentation stages. Specifically, Lactobacillus acetotolerans, Acetobacter pasteurianus, Agrobacterium larrymoorei, Stenotrophomonas maltophilia, Xanthomonas sacchari, Saccharomyces unclassified, and Alternaria unclassified were identified as the predominant microorganisms during the acetic acid fermentation phase. Further investigation revealed that pH, moisture content, vinegar pei temperature, and non-volatile acids were the primary drivers of microbial succession. Additionally, a detailed metabolic network of flavor compounds in closed solid-state vinegar was successfully constructed. This research not only deepens our comprehension of the complex interplay between microbial communities and flavor quality but also provides essential insights for refining fermentation processes and improving flavor profiles in industrial-scale closed solid-state vinegar production systems.

Vinegar is traditionally produced by fermentation with a mixed system composed of naturally inoculated microorganisms. The complex microbial communities in the fermentation system are crucial to the formation of vinegar flavor. Studies on the microbial communities and their interactions are helpful to reveal the relationship between microorganisms and the quality of vinegar and are of great significance for targeted regulation of microorganisms in the fermentation process, productivity enhancement and vinegar quality improvement. Therefore, recent studies on the microbial diversity and the interactions among core functional microorganisms in the traditional fermentation process of vinegar are reviewed in this paper. Moreover, the positive effects of the interaction among core functional microorganisms on the flavor of vinegar are discussed. Finally, the problems existing in the current research are summarized. This review is expected to provide a reference for targeted regulation of vinegar quality.

In the traditional solid-state fermentation system, the temperature and humidity fluctuations inside and outside the fermented grains in summer cause poor flavor quality of vinegar. To address this issue, this study integrated high performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), an electronic tongue and sensory evaluation to compare the changes and differences in various indices between closed and traditional solid-state vinegar fermentation under different fermentation conditions. The results showed that closed solid-state fermentation exhibited higher efficiency than traditional solid-state fermentation in terms of temperature control, total acid content, non-volatile acid generation rate and reducing sugar consumption rate. Vinegar produced by closed solid-state fermentation showed higher proportion of non-volatile organic acids, faster production of umami free amino acids, and a larger number of volatile flavor compounds, indicating milder taste and more pronounced textural layers. Sensory evaluation showed that the vinegar showed a distinct sour and umami taste with more refreshing overall mouthfeel. In general, closed solid-state fermentation has significant advantages and potential in improving both the fermentation efficiency and product quality, laying a theoretical foundation for stable and high-yield Zhenjiang vinegar production.

A closed solid-state fermentation system refers to a system that automatically and intelligently completes solid-state fermentation under closed and controllable conditions to stabilize product quality, reduce labor intensity and improve intelligence level. In recent years, with the transformation and upgrading of the traditional brewing industry and with the increasingly urgent need to promote intelligent manufacturing, the research and development of closed solid-state fermentation systems have attracted more and more attention from the industry and researchers. In this paper, the monitoring methods for closed solid-state fermentation systems are reviewed from three perspectives: the application of various monitoring equipment and methods, the development of various mathematical models and control strategies, and the optimization of monitoring equipment using various control strategies. In addition, this review introduces the regulation strategies for closed solid-state fermentation systems in order to provide a theoretical basis for improving existing solid-state fermentation systems and developing new ones in the future.

Rum fermentation is driven by microbial consortia dominated by yeast. The interactions among yeasts in the fermentation system are the key to the formation of rum flavor. Investigating the interactions between Saccharomyces cerevisiae and non-Saccharomyces yeast species will contribute to understanding the relationship between yeast and rum quality, which is of great significance for fermentation process control, production efficiency improvement and rum quality enhancement. In this article, the microbial community diversity and the interactions among yeasts during rum fermentation are reviewed. Furthermore, the beneficial effects of co-fermentation with S. cerevisiae and non-Saccharomyces yeasts on the flavor quality of rum are also summarized. Finally, the limitations of current research are discussed in order to provide a theoretical basis for improving the flavor quality of rum.

The brewing of solid vinegar is traditionally carried out in an open solid-state fermentation system, which is susceptible to environmental factors, leading to unstable flavor quality, low degree of mechanization and low labor productivity. Compared with the traditional open solid-state fermentation system, the closed solid-state fermentation system is not disturbed by external environmental factors, and allows mechanized and automated vinegar brewing, which is beneficial for stabilizing product quality, improving labor productivity, and promoting the modernization of the vinegar industry. In recent years, the closed solid-state fermentation system has been widely used in the field of vinegar brewing, which has brought significant improvement to the production efficiency of solid-state fermented vinegar. This article introduces the structure, characteristics, and regulatory measures of common closed solid-state fermentation systems. Besides, the factors affecting the fermentation performance of the closed solid-state fermentation system are summarized, the application of the closed solid-state fermentation system in vinegar brewing is briefly discussed, and an outlook on future trends in the development of an automatic and intelligent closed solid-state fermentation system is given. We hope that this review can provide a reference for the development of a new closed solid-state vinegar system in the future.