One of the 3,600-Year-Old Tarim mummies from the Xiaohe cemetery in China, with kefir cheese samples (highlighted with red triangles) scattered around its neck. Image credit: Wenying Li
In a remarkable discovery, researchers have identified the world’s oldest cheese on 3,600-year-old mummies in China’s Tarim Basin. This finding sheds light on ancient food practices and provides insights into the evolution of dairy fermentation techniques.
The enigmatic white substance, found smeared on the heads and necks of mummies at the Xiaohe Cemetery in northwestern China, was initially discovered about two decades ago. Recent DNA analysis has revealed that this substance is kefir cheese, a type of probiotic soft cheese. The researchers published their findings in the journal Cell on September 25.
Kefir cheese is produced through the fermentation of milk using kefir grains, which are symbiotic cultures containing a mix of bacteria and yeast. It is these complex microbial cultures that ferment milk into cheese, similar to how a sourdough starter works for bread. This ancient cheese sample contained several bacterial and fungal species, including Lactobacillus kefiranofaciens and Pichia kudriavzevii, both of which are found in modern-day kefir grains.
The three kefir samples taken. Image credit: Wenying Li
The preservation of food items like cheese over thousands of years is extremely rare, making this discovery particularly valuable for understanding ancient diets and cultural practices. The researchers were able to extract DNA from the cheese samples and analyze it using advanced techniques, including DNA capture and shotgun sequencing. According to Qiaomei Fu, a paleontologist at the Chinese Academy of Sciences, the study of this ancient cheese offers a unique glimpse into the diet and culture of the Xiaohe people.
One of the intriguing aspects of this discovery is the presence of both cow and goat DNA in the cheese samples. This suggests that the Bronze Age Xiaohe population used milk from different ruminants to produce their cheese. Interestingly, the bovine and caprine milk appear to have been used separately rather than mixed, unlike some modern cheese-making practices.
Wearing Western-influenced textiles and possessing surprising technologies and customs, the origin of the fair-skinned Xiaohe population is a mystery. Photo: elaine
The production of cheese through fermentation may have been a practical solution for the Xiaohe population, who were likely lactose intolerant. Fermentation reduces the lactose content in milk, making it more digestible for those who cannot tolerate lactose. This technique not only extended the shelf life of raw milk but also made it possible for lactose-intolerant individuals to consume dairy products.
By examining the mitochondrial DNA of the goats used in cheese production, the researchers were able to trace connections between the Xiaohe population and other ancient groups. The goat DNA clustered closely with Neolithic, Chalcolithic, and Bronze Age European and Central Asian samples, suggesting interactions between steppe populations and the Xiaohe people.
The Xiaohe Cemetery where the mummies were found in boat-shaped coffins. Photo: Li et al. / Zhang et al.
The study also provided insights into the microbial community present in the ancient kefir cheese. Despite being exposed to the environment for thousands of years, some samples showed surprisingly little contamination from external bacteria. This resistance to contamination may have been crucial for the production of kefir cheese in ancient times when understanding of microbiology was limited.
One of the most significant findings of the study was the reconstruction of ancient Lactobacillus kefiranofaciens genomes. By comparing these ancient genomes with those of modern L. kefiranofaciens strains, the researchers were able to trace the spread of kefir-making techniques across Eurasia.
Xiaohe man. Photo: Martonkurucz
The analysis revealed two distinct spreading routes for different subspecies of L. kefiranofaciens. One route, associated with the subspecies kefirgranum, appears to have spread from the Northern Caucasus to Europe and coastal regions of East Asia. The other route, linked to the subspecies kefiranofaciens, suggests a spread from Xinjiang to other regions in inland East Asia, such as Tibet and the Gan-Qing area.
This discovery not only illuminates the cultural exchanges between ancient populations but also demonstrates how human activities have influenced microbial evolution. The researchers identified several instances of horizontal gene transfer in the L. kefiranofaciens genomes, suggesting ongoing adaptation of these bacteria to their environment and human practices.
Map of Eurasia showing the location of the Xiaohe cemetery, the Tarim Basin, the ancient Silk Road routes and the areas occupied by cultures associated with the settlement of the Tarim Basin. Image: Li et al.
Some of the transferred genes were related to stress response, defense against phage infections, and interactions with human hosts. These adaptations likely helped the bacteria survive in various ecological niches and may have been selected for by humans over time as they propagated preferred strains of kefir.
The study also raises questions about the purpose of smearing cheese on the mummies. While the exact reason remains unknown, it adds another layer of intrigue to our understanding of ancient burial practices and beliefs.
The beauty of a Xiaohe woman. Photo: Michael Kan
This research demonstrates the potential of modern scientific techniques like DNA analysis in unraveling the mysteries of the past. The discovery of the world’s oldest cheese on these ancient mummies opens up new avenues for understanding the development of food preservation techniques, the spread of dairy farming, and the complex interactions between humans and microbes throughout history.