Shanghai Scientists Reveal Organic Acids Boost Yeast Growth and Ethanol Output in Huangjiu Fermentation

Researchers at the Shanghai Institute of Microbiology have published new findings on how organic acids influence the microbial communities during the fermentation of Huangjiu, a traditional Chinese rice wine. The study, released in npj Science of Food, used advanced techniques such as flavoromics and metatranscriptomics to analyze 44 compounds that affect the fermentation process.

Huangjiu is produced through the fermentation of glutinous rice, and its quality depends heavily on the activity of various microorganisms. However, until now, the specific role of organic acids in shaping these microbial communities was not well understood. The research team compared two groups of Huangjiu fermentations: one with high levels of organic acids (H group) and another with low levels (L group). Samples were collected from a major producer in Zhejiang province at different stages over a 35-day fermentation period.

The analysis showed that total sugar content declined more rapidly in the H group, while ethanol content increased faster after the first week, reaching 23.1% by the end of fermentation—higher than in the L group. The H group also had a 14.71% higher total acid content compared to the L group. Amino acid nitrogen content remained similar between both groups.

Using gas chromatography-mass spectrometry, researchers identified 44 volatile flavor compounds in both groups. While most compounds did not differ significantly between groups, some—such as isoamyl alcohol and ethyl butyrate—were found at higher concentrations in the H group by the end of fermentation.

Microbial community analysis revealed that lactic acid bacteria dominated both groups, but their abundance patterns differed over time. In terms of fungi, Saccharomyces and Thermomyces were more prevalent in the H group, while Aspergillus was more common in the L group.

The study focused on how specific organic acids affected these key microorganisms. Succinic acid was found to have a positive correlation with Saccharomyces and Thermomyces populations. Laboratory experiments confirmed that adding succinic acid at low concentrations promoted Saccharomyces cerevisiae growth and increased ethanol production by up to 32%. In contrast, high concentrations of lactic acid and tartaric acid inhibited yeast growth.

Metatranscriptomic analysis provided further insight into how these acids affect gene expression during fermentation. In the H group, genes involved in sugar metabolism and ethanol production were upregulated, especially those related to glycolysis and the tricarboxylic acid (TCA) cycle. This upregulation was linked to higher succinic acid levels and greater metabolic activity in Saccharomyces cerevisiae.

The findings suggest that endogenous organic acids play a regulatory role in shaping microbial community structure and function during Huangjiu fermentation. By understanding these interactions, producers could potentially manage organic acid levels to steer microbial succession, optimize fermentation performance, and improve product quality.

The study also highlights possible applications for other traditional fermented beverages where complex microbial communities are involved. The authors note that while their experiments were conducted under controlled laboratory conditions, further research is needed to validate these results at an industrial scale and to establish causality through targeted metabolic studies.

This research provides new perspectives for precision management of fermentation processes by focusing on organic acid regulation rather than relying solely on environmental factors like temperature or humidity. Such approaches could help stabilize microbial communities, reduce spoilage risks, and produce Huangjiu with more consistent sensory profiles.

The data supporting these findings are available from the corresponding authors upon request. The study was supported by several public projects and university funds in Zhejiang Province and Shaoxing city.