"This is the oldest known cheese sample ever discovered in the world," says Qiaomei Fu, the paper's corresponding author at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. "Food items like cheese are extremely difficult to preserve over thousands of years, making this a rare and valuable opportunity. Studying the ancient cheese in great detail can help us better understand our ancestors' diet and culture."

About two decades ago, a team of archaeologists discovered mysterious white substances smeared on the heads and necks of several mummies found in the Xiaohe cemetery in Northwestern China's Tarim Basin. These mummies date back to about 3,300 to 3,600 years ago, from the Bronze Age. At the time, scientists thought these substances might be a type of fermented dairy product, but they couldn't identify exactly what kind.

After more than a decade of advancements in ancient DNA analysis, a team led by Fu has unraveled the mystery.

The researchers successfully extracted mitochondrial DNA from samples found in three different tombs at the cemetery. They identified cow and goat DNA in the cheese samples. Interestingly, the ancient Xiaohe people used different types of animal milk in separated batches, a practice differing from the mixing of milk types common in Middle Eastern and Greek cheesemaking.

Most importantly, Fu and her colleagues managed to recover the DNA of microorganisms from the dairy samples and confirmed that the white substances were in fact kefir cheese. They discovered that the samples contained bacterial and fungal species, including Lactobacillus kefiranofaciens and Pichia kudriavzevii, both commonly found in present-day kefir grains.