The identification of processed plant foods is one of the most stubborn challenges in archaeobotany. Whole seeds and grains survive charring in recognizable form, preserving the diagnostic shapes of seed coats, embryos, and internal cell structures that allow specialists to assign remains to species. But once ancient cooks crushed, ground, or kneaded their ingredients, that diagnostic architecture was destroyed. What remains after charring is an amorphous lump of fused plant tissue, a feature that archaeologists often record generically as charcoal or food residue and move past. The Yongsan-dong lumps could easily have been dismissed as shapeless burnt debris had the researchers not subjected them to a battery of analytical tests.

Microscopic examination of the lumps revealed that they consisted exclusively of soybean tissue, with no evidence of other plant materials mixed in. This monocultural composition was itself informative. A lump of accidental kitchen waste or general fuel residue would be expected to contain a heterogeneous mixture of plant matter. Instead, the material was uniformly soybean, suggesting deliberate processing of a single ingredient. The researchers then turned to stable isotope analysis, measuring the ratios of carbon-13 to carbon-12 and nitrogen-15 to nitrogen-14 in the charred remains. Carbon isotope values in plants reflect the photosynthetic pathway of the species concerned, and soybean, as a C3 plant with a distinctive isotopic signature, could be distinguished from C4 crops such as millet. Nitrogen isotope values added a further line of evidence, since legumes like soybean fix atmospheric nitrogen through their symbiotic relationship with soil bacteria, giving them characteristically low nitrogen isotope ratios compared with plants that depend on soil nitrogen alone.

Isotopic data alone could not settle the question of how the soybeans had been processed, so the team turned to experiment. Under controlled laboratory conditions, they carbonized whole soybeans as well as soybean-based food products, replicating the charring that occurs when food is accidentally burnt or discarded into a fire. The morphological changes that whole beans undergo during carbonization are well documented: seeds swell, crack, and distort in predictable ways. The ancient lumps did not match the appearance of charred whole beans. Instead, the experimental results indicated that the archaeological material had been shaped into a dough-like form before it was charred, meaning the soybeans had been crushed and reconstituted into a compact mass prior to their encounter with fire.

The closest modern analogue for such a product is meju, the traditional Korean fermented soybean block that serves as the foundation for doenjang, Korea’s fermented soybean paste, and for kanjang, its soy sauce. In the traditional production process, whole soybeans are boiled, crushed, and formed into dense blocks that are then allowed to ferment, during which naturally occurring molds and bacteria break down proteins and generate the deep savory flavors, the umami compounds, that define Korean fermented foods. The researchers are careful to note a crucial limitation: fermentation itself cannot be directly demonstrated in the charred remains. Microbial activity leaves no morphological trace that survives carbonization, and the lumps could in principle represent an unfermented dough product. What the evidence does establish is that the processing step, the transformation of whole beans into compact masses, existed by the early centuries AD.

To test whether the Yongsan-dong lumps were an isolated curiosity or part of a broader pattern, the researchers extended their investigation to similar amorphous remains from four additional archaeological sites on the southern Korean Peninsula. The comparative analysis corroborated the interpretation, suggesting that the practice of processing soybeans into lumps was established across the region as early as AD 200, with related remains continuing into the following centuries. This chronological and geographic spread places the practice squarely within the period of early state formation on the peninsula, the era of the Samhan polities that preceded the Three Kingdoms, when agricultural intensification and social stratification were transforming Korean society.

The functional logic of processing soybeans into compact masses is compelling from the standpoint of food storage. Whole dried soybeans store reasonably well, but they are vulnerable to pests, moisture, and spoilage, and they require lengthy cooking before consumption. Crushing the beans and forming them into dense blocks reduces their volume, concentrates their nutrients, and creates a product that can be stored for extended periods and reconstituted as needed. Fermentation, when it occurs, adds a further preservation benefit by producing acids and antimicrobial compounds that inhibit spoilage organisms, while simultaneously generating the amino acids and flavor compounds that make fermented paste such a potent seasoning. In other words, the same process that kept food edible through lean seasons also made it delicious, a convergence of necessity and pleasure that characterizes many of the world’s great fermented food traditions.

Historical and ethnographic sources enrich this material picture. Early Korean historical texts, including the Samguk Sagi, the twelfth-century history of the Three Kingdoms, contain references to fermented soybean products, and later ethnographic documentation records the central place of jang, the family of fermented soybean condiments, in Korean household economy. Traditional meju production was a domestic activity, typically carried out by households in late autumn, with soybean blocks hung from rafters to ferment over the winter. The archaeological lumps suggest that the technological and culinary knowledge underpinning this tradition was already in place well over a millennium before such documentary records, pushing the deep history of Korean fermented foods back to the early centuries of the Common Era.

The study also speaks to broader questions in the archaeology of food. Soybean is a legume of remarkable nutritional value, rich in protein and, through its biological nitrogen fixation, beneficial to the soils in which it is grown. Archaeobotanical work has traced soybean cultivation in East Asia over thousands of years, but the archaeological record of how ancient peoples transformed the raw bean into food has remained thin, dominated by finds of whole seeds that say little about cuisine. By demonstrating that amorphous charred lumps can be identified to species and assigned to processing stages through the combined application of microscopy, stable isotope analysis, and experimental charring, the researchers offer a methodological template that other archaeobotanists can apply to shapeless plant remains elsewhere in the world.

The social dimensions of the find are equally intriguing. Fermented condiments occupy a special position in Korean foodways, functioning not merely as flavorings but as markers of household identity, seasonal rhythm, and, in stratified societies, status. Previous research on foodways in the ancient Baekje Kingdom has shown that feasting and culinary practice were entangled with social differentiation, and the emergence of a paste-making technology in the early centuries AD may reflect both the agricultural surpluses and the developing tastes of increasingly complex societies. Whether the Yongsan-dong lumps represent everyday household provisioning, communal food preparation, or something more ceremonial cannot be determined from the charred evidence alone. What can be said is that nearly two millennia ago, communities on the southern Korean Peninsula were already manipulating soybeans in ways that their descendants would refine into a culinary tradition that continues to shape Korean identity, and global appetites, today.

Subject of Research: Archaeobotanical identification of processed soybean remains from ancient Korean sites and their implications for legume storage and culinary practices

Article Title: Processed soybean remains from ancient Korean sites: archaeobotanical insights into legume storage and culinary practices

Article References: Kim, M., & Song, G.-S. (2026). Processed soybean remains from ancient Korean sites: archaeobotanical insights into legume storage and culinary practices. Archaeological and Anthropological Sciences, 18(11), Article 213. https://doi.org/10.1007/s12520-026-02580-9

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02580-9

Keywords: soybean, archaeobotany, fermented soybean paste, meju, stable isotope analysis, Korea, food storage, culinary practices, charred plant remains, Yongsan-dong, legume processing, ancient foodways

The team focused on three iconic Korean fermented soybean products: cheonggukjang, doenjang, and meju. Although all three begin with boiled soybeans, they diverge dramatically in their fermentation conditions, microbial communities, and resulting chemistry. Cheonggukjang is fermented briefly and with little salt, allowing Bacillus species to dominate. Doenjang undergoes prolonged maturation in a high-salt environment that reshapes its microbial ecology. Meju, the fermented soybean brick that serves as the foundation for both doenjang and soy sauce, is dominated by fungi such as Aspergillus species and is rich in the enzymes and metabolites those microbes generate. Because these pastes are known to contain bioactive compounds with antioxidant, anti-inflammatory, and immunomodulatory properties, the researchers reasoned that their extracts might act as functional starter ingredients rather than mere flavorings.

To test the idea, the scientists prepared extract solutions from commercially purchased cheonggukjang, doenjang, and meju by diluting each paste 1:100 in distilled water, then centrifuging and filtering the mixture. Each extract was inoculated at 0.5 percent by volume into 400 milliliters of milk cream. A control butter was fermented with a commercial starter containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. All creams were fermented at 37 degrees Celsius for 24 hours, aged at 4 degrees Celsius for 12 hours, and then churned at 280 revolutions per minute for 15 minutes. The resulting butters were subjected to a battery of analyses covering pH, color, viscosity, moisture and fat content, microbial counts, electronic nose and electronic tongue profiling, and a sensory evaluation by a sixteen-member trained panel.

The pH results immediately revealed a fundamental biochemical divide. Butters fermented with the soy paste extracts had significantly higher pH values than the control, with the cheonggukjang sample highest of all. The explanation lies in the contrasting metabolisms of the microbial communities involved. Commercial lactic acid starter cultures flood the cream with lactic acid early in fermentation, driving pH down. The mixed communities drawn from traditional pastes, by contrast, include fungi and Bacillus species that decompose proteins and deaminate amino acids, releasing ammonia and other alkaline metabolites that push pH upward. The authors suggest this milder acidity may actually benefit the product, reducing sourness while allowing flavor-producing microbes to remain metabolically active, potentially enhancing both flavor quality and the delivery of probiotic organisms.

Physical properties told a reassuring story for manufacturers. Viscosity showed no significant differences among any of the butters, treated or control. Butter’s high-fat water-in-oil matrix provides substantial emulsification stability, and the small quantities of microbial metabolites generated during fermentation were simply not enough to alter its flow behavior. This means soy paste extracts can be incorporated without compromising the texture consumers expect. Color, however, did change: the meju and cheonggukjang butters were significantly more yellow than the control and the doenjang butter. Bacillus species abundant in these pastes produce peptides, free amino acids, and Maillard reaction products during fermentation, while molds and yeasts can promote browning reactions between reducing sugars and amino acids. The yellowness matters commercially, because previous research has shown that consumers associate a deeper golden hue in butter with higher purchase intention.

Microbial counts exposed the most striking differences. Total plate counts were significantly higher in all three extract-fermented butters than in the control, with cheonggukjang butter highest, reflecting its Bacillus-rich, low-salt, short-fermentation origin. Lactic acid bacteria counts were also elevated in all treated samples, but here meju butter took the lead. The researchers attribute this to Aspergillus oryzae, the fungus central to meju fermentation, whose powerful enzymes break proteins and carbohydrates into low-molecular-weight compounds that effectively feed lactic acid bacteria. Meju-derived communities also showed greater tolerance and adaptability to environmental stress than freeze-dried commercial strains. The doenjang-derived bacteria, adapted to high-salt conditions, grew more slowly in butter’s low-salt, high-fat environment, while cheonggukjang organisms, adapted to high water activity, were similarly constrained in the low-moisture product.

The flavor chemistry was mapped with an electronic nose, which identified elevated levels of volatile compounds including trimethylamine, ethanethiol, ethyl acetate, 2-methylbutanal, 3-methyl-1-butanol, and propyl acetate in the extract-fermented butters. Ethyl acetate, associated with buttery and fermented notes, was markedly higher in the meju butter. Principal component analysis of the aroma data achieved a discrimination index of 88, with the first principal component alone explaining 97.4 percent of the variance, cleanly separating the control from the treated samples and distinguishing the treated samples from one another. Notably, the sulfurous, rancid, and beany flavors often associated with fermented soybean products were not detected in the finished butter, suggesting the extracts can contribute desirable fermented aromas without importing off-flavors.

The electronic tongue added a taste dimension. Extract-fermented butters scored higher than the control in sourness, saltiness, and umami. The elevated sourness tracked with lactic acid bacteria counts, since more bacteria meant more organic acids. Saltiness was highest in the doenjang butter, consistent with residual salts carried over from its brine-fermented origin. Umami, measured against a monosodium glutamate reference, was highest in the meju butter, reflecting its greater content of glutamic acid, small peptides, and nucleotides released by the proteolytic activity of Aspergillus and Bacillus enzymes. Interestingly, the taste-based principal component analysis showed minimal differences among the three treated butters, indicating that despite their different origins, the pastes share overlapping microbial communities and metabolite profiles that converge in the finished dairy matrix.

The sensory panel delivered the verdict that matters most to consumers. The meju butter scored highest in flavor, taste, absence of off-flavor, and overall acceptability, and together with the cheonggukjang butter earned the top appearance scores, mirroring the color measurements. Panelists rated all extract-fermented butters higher than the control for texture attributes, likely because metabolites such as melanoidins, polyphenols, and peptides disperse within the fat matrix and moderate greasiness. The authors caution that their extracts contained both microorganisms and metabolites, so the observed effects reflect their combined action, and further microbiological work will be needed to separate the two. Still, the conclusion is clear: meju extract in particular can meaningfully improve the quality, microbial profile, and sensory appeal of fermented butter. As demand grows for dairy products that offer health benefits beyond basic nutrition, this study suggests that centuries-old Korean fermentation wisdom may have a place on the modern breakfast table, one golden, umami-rich pat at a time.

Subject of Research: Use of Korean traditional fermented soy paste extracts as starter ingredients to improve the quality and sensory properties of fermented butter

Article Title: Quality properties of fermented butter using extract solution from Korean traditional fermented pastes

Article References: Jeong, Y.-S., Yong, H. I., & Park, S.-Y. (2026). Quality properties of fermented butter using extract solution from Korean traditional fermented pastes. Food Science of Animal Resources, 46(1), Article 92. https://doi.org/10.1007/s44463-026-00089-2

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00089-2

Keywords: fermented butter, Korean fermented soy paste, meju, doenjang, cheonggukjang, lactic acid bacteria, electronic nose, electronic tongue, sensory evaluation, food fermentation, dairy quality, umami