Scientists Decode the Microbial Alchemy Behind China’s 2,000-Year-Old Sour Meat

In ceramic jars buried in the kitchens of Guizhou Province, China, a quiet microbial revolution has been unfolding for more than two thousand years. Sour meat, a traditional fermented pork product made by sealing sliced pork belly with salt and glutinous rice flour, owes its distinctive tangy aroma and rich taste to an invisible ecosystem of bacteria and fungi. Now, a research team led by Xiefei Li of Guizhou Medical University has mapped that ecosystem with unprecedented precision, revealing exactly which microbes drive the transformation of raw pork into a flavor-packed delicacy. The findings, published in Food Chemistry: X, could finally bring this ancient craft into the era of industrial standardization.

The challenge facing food scientists has long been a technical blind spot in how microbial communities are measured. Conventional high-throughput sequencing reports only relative abundance, essentially the percentage share of each microbe in a sample. That approach can mask dramatic shifts in total microbial load, making it impossible to know whether a species is genuinely proliferating or simply riding along as other populations collapse. To overcome this, the team employed quantitative microbiome profiling using synthetic DNA spike-in standards. Twelve prokaryotic 16S rRNA gene sequences, each roughly 1,500 base pairs long and carrying five primer-binding sites, were added to every sample at four known concentrations ranging from 10^3 to 10^6 copies. By comparing amplification signals from these internal standards against native microbial DNA, the researchers converted relative percentages into absolute cell counts per gram of meat, providing a biologically meaningful picture of microbial succession.

The results were striking. During the first 28 days of fermentation, total bacterial abundance surged from 10^6 to 10^9 copies per gram, an exponential growth phase that relative sequencing would have completely obscured. At day zero, Proteobacteria dominated the raw meat at 5.6 × 10^6 copies per gram, roughly 71 percent of the total microbial load. But within two weeks, Firmicutes had taken over, exploding from 8.0 × 10^5 to 1.0 × 10^9 copies per gram and representing 99 percent of all bacterial DNA, a dominance maintained through the remaining fermentation period. At the genus level, Escherichia–Shigella initially led with 2.0 × 10^6 copies per gram, but was rapidly displaced by Weissella, which jumped from 2.6 × 10^5 to 5.8 × 10^8 copies per gram by day 14, marking the onset of significant acid production. By day 28, Staphylococcus had become the predominant genus at 1.1 × 10^9 copies per gram, a position it held through day 70, likely thanks to its remarkable tolerance of acidic and saline conditions.

Fungi followed a parallel trajectory. Nine fungal phyla were identified, with Ascomycota expanding from 2.6 × 10^5 to 1.5 × 10^8 copies per gram and ultimately comprising 99 percent of total fungal DNA. Cladosporium dominated the fresh meat at 1.1 × 10^5 copies per gram, but by day 14 Candida had surged from a mere 1.2 × 10^3 to 7.7 × 10^6 copies per gram, eventually reaching 10^8 copies per gram and accounting for roughly 90 percent of the total fungal load in later stages. Candida metabolizes glucose into ethanol and carbon dioxide via the Embden–Meyerhof–Parnas pathway and generates additional alcohols through the Ehrlich pathway, while also producing esterases that catalyze ester formation. Debaryomyces, the second most abundant fungal genus, is widely recognized in fermented meats as an ester-producing species with proteolytic and lipolytic activities and strong adaptability to high salinity, low pH, and reduced water activity.

To capture the flavor chemistry unfolding alongside these microbial shifts, the team deployed two complementary volatile analysis platforms. Headspace–gas chromatography–ion mobility spectrometry identified 61 monomeric volatile compounds, including 18 alcohols, 19 esters, 4 aldehydes, and 4 ketones, while headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry detected 89 volatiles, among them 29 esters, 13 aldehydes, and 8 acids. Orthogonal partial least squares discriminant analysis distilled these datasets down to 17 and 37 key aroma contributors, respectively. The volatile fingerprint revealed a clear biphasic evolution. During the first 28 days, alcohols such as propanol, hexanol, and 2-pentanol were significantly enriched, alongside aldehydes and ketones, likely derived from microbial fermentation and lipid oxidation. After day 28, a marked decline in these early-stage compounds coincided with a surge in esters, particularly ethyl acetate, ethyl butanoate, propyl butanoate, butyl butanoate, and ethyl hexanoate, which became the predominant volatiles through day 70.

This ester transition represents the biochemical maturation of sour meat. Esters form through esterification reactions between short-chain fatty acids and alcohols, and they impart the fruity, sweet, floral, and creamy notes that define the product’s characteristic aroma. Interestingly, ethyl tridecanoate, ethyl pentadecanoate, and ethyl undecanoate peaked on day 42 before declining, a rise–fall pattern the researchers attribute to acid-catalyzed ester hydrolysis breaking these compounds back down into their constituent alcohols and acids. Meanwhile, aldehydes such as heptanal and octanal, which contribute citrus-like scents, dominated day 28 samples. Heptanal arises from the oxidative degradation of linoleic and arachidonic acids, whereas octanal originates from oleic acid oxidation. By day 70, volatile acids had increased significantly, and (Z)-9-tetradecenal, known for floral, fruity, and herbal notes, reached its highest concentration, suggesting that prolonged fermentation intensifies lipid degradation and oxidation while enriching the meat in ethyl esters and carboxylic acids.

Non-volatile taste compounds were tracked using ultra-performance liquid chromatography–quadrupole time-of-flight tandem mass spectrometry, which identified 54 metabolites with variable importance in projection scores above 1, including amino acids and their derivatives, fatty acids, and nucleotides. Total free amino acids increased significantly over fermentation, peaking at day 70, though their high sensory thresholds suggest they contribute more as precursors than as direct taste agents. Umami peptides accumulated progressively through day 70, their savory character deriving primarily from glutamic acid and aspartic acid residues in peptide-bound form. These peptides rarely impart a singular taste, instead exhibiting complex sensory properties including sourness, sweetness, or mild bitterness that enrich the multidimensional flavor profile. Notably, concentrations of AMP and IMP nucleotides decreased significantly following fermentation, indicating that the distinctive umami and aromatic attributes of sour meat are governed primarily by lipid oxidation and amino acid degradation products rather than nucleotide-derived taste modulators.

Spearman correlation analysis wove these threads together, linking 20 dominant microbial genera, 10 bacterial and 10 fungal, to 87 flavor compounds. Most esters and several organic acids showed significant positive correlations with Staphylococcus and Candida, with correlation coefficients exceeding 0.75. Staphylococcus has been implicated in the biosynthesis of ethyl palmitate, ethyl oleate, ethyl decanoate, ethyl myristate, and ethyl stearate, and is estimated to mediate the proteolytic degradation of over 40 percent of proteins and peptides in fermented meat products. The genus also correlated strongly with free amino acids and umami-active peptides such as aspartyl-phenylalanine and glutamyl-isoleucine. Hexanoic acid, 2-hydroxystearic acid, and related organic acids were similarly correlated with both Staphylococcus and Candida, positioning these two genera as the principal functional microbiota statistically associated with both volatile and non-volatile flavor formation.

Functional prediction using PICRUSt2, based on Kyoto Encyclopedia of Genes and Genomes orthology annotations, added a mechanistic layer to the story. Predicted enzyme-encoding genes involved in substrate degradation and flavor biosynthesis increased progressively through fermentation, peaking at day 42, coinciding with the exponential growth phase of the microbiota. The predicted metabolic network traces glutinous rice flour starch hydrolyzed by glucoamylase and α-amylase into glucose, which is then funneled through glycolysis to pyruvate, a central precursor for organic acids, alcohols, and esters. Pyruvate can be converted to lactic acid, acetic acid, and ethanol via L-lactate dehydrogenase, pyruvate oxidase, and alcohol dehydrogenase, or channeled into the tricarboxylic acid cycle through pyruvate dehydrogenase. In parallel, lipases catalyze the conversion of fatty acids into volatile esters, while branched-chain amino acid transaminase and dihydroxy-acid dehydratase link proteolysis to the production of higher alcohols.

The authors acknowledge that their sequencing data were analyzed at the genus level and cannot resolve species- or strain-level functional heterogeneity, and that correlation alone cannot prove causation. The spike-in quantification method detects both viable and non-viable cells, meaning the late-stage plateau in DNA copies may partly reflect residual DNA from dead microbes rather than true growth stagnation. Future work combining viability qPCR or plate counting will help distinguish live-cell dynamics. Nevertheless, the study delivers actionable insights for the rational design of synthetic starter consortia. By identifying Staphylococcus, Weissella, and Candida as stage-specific functional drivers, the research lays the groundwork for targeted inoculated fermentation that could standardize sour meat production, reduce batch variability, and bring this two-millennium-old tradition into modern food manufacturing.

Subject of Research: Microbial community dynamics and flavor compound formation during traditional Chinese sour meat fermentation

Article Title: Microbial community evolution and flavor formation during sour meat fermentation: Integrated quantitative microbiome profiling, HS-SPME-GC–MS, and UPLC-Q-TOF-MS/MS

Article References: Li, X., Yang, J., Yuan, X., Lou, Y., Ding, Y., Zhou, Y., Luo, P., & Pan, D. (2026). Microbial community evolution and flavor formation during sour meat fermentation: Integrated quantitative microbiome profiling, HS-SPME-GC–MS, and UPLC-Q-TOF-MS/MS. Food Chemistry: X, Article 104625. https://doi.org/10.1016/j.fochx.2026.104625

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104625

Keywords: food science, fermentation, microbiome, flavor chemistry, quantitative microbiome profiling, sour meat, Microbial, community, evolution, flavor, formation, during