Yimin Yang and Yusheng Liu
Lumps of cheese, shown with arrowheads, were collected from the neck and chest of a female mummy known as the "Beauty of Xiaohe." Inset shows an enlarged view of a cheese lump.
The world's oldest cheese has been found on the necks and chests of perfectly preserved mummies buried in China's desert sand.
Dating back as early as 1615 B.C., the lumps of yellowish organic material have provided direct evidence for the oldest known dairy fermentation method. The individuals were likely buried with the cheese so they could savor it in the afterlife.
Although cheese-making is known from sites in northern Europe as early as the 6th millennium B.C. and was common in Egypt and Mesopotamia in 3rd millennium B.C., until now no remains of ancient cheeses had been found.
The 3,600-year-old cheese was discovered during archaeological excavations carried between 2002 and 2004 at the Xiaohe cemetery, in the inhospitable Taklamakan desert in northwestern China, lead by Idelisi Abuduresule from Cultural Relics and Archaeology Institute, Ürümchi.
Also known as Small River Cemetery Number 5, the burial was first discovered in 1934 by Sweden archaeologist Folke Bergman and it's part of several archaeological sites spread in the Tarim Basin.
The cemetery was built on a large natural dune and houses hundreds of mysterious mummies with Caucasian features, buried into massive wooden coffins resembling upside-down boats.
"Recent DNA studies showed the population of these sites was mixed, European and Asian," Anna Shevchenko, proteomics specialist in Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany, told Discovery News.
Taklamakan literally means "go in and you won't come out." The area, with its salty, hyper-dry sands, extreme hot in summer and cold in winter, provided the perfect conditions for natural mummification.
Moreover, the boat-like coffins were covered by several layers of cowhide, which sealed them from air, water and sand as if they had been "vacuum-packed."
Skin and hair, baked onto the dehydrated corpses, remained almost intact, as well as woolen textiles, plant seeds, woven grass baskets and clumps of organic material around the neck and chest of the mummified bodies. No pottery was found that could be associated with making or consuming food.
The researchers lead by Chinese team leader Changsui Wang from the University of Chinese Academy of Sciences collected 13 samples of the yellowish organic material from 10 tombs and mummies, which included the so-called "Beauty of Xiaohe" -- a 3,800-year-old female mummy wrapped in a finely crafted shroud, bearing Caucasian features such as a long nose and light hair.
Protein analysis performed in Dresden showed the organic material wasn't butter or milk, but a cheese made by robust, easily scalable kefir fermentation. Shevchenko explained that such analysis is common in medical and biological science, but not in archaeology.
"Usually, proteins are either ignored or protein bulk content is estimated to characterize the nutritional properties," Shevchenko said.
"According to common belief, they are difficult to recover from the sample matrix, totally degraded and samples heavily contaminated by environment, therefore the analyzed are hardly meaningful," she added.
A full-body view of the "Beauty of Xiaohe" after the mummy was unwrapped.Yimin Yang and Yusheng Liu
But according to the researchers, who have detailed their finding in an upcoming issue of the Journal of Archaeological Science, proteins do survive under extreme conditions. Furthermore, in contrast to commonly analyzed lipids, they may bear the hallmarks of technological processes used to prepare the food. Altogether, they can be highly informative molecules.
"Our work opens new perspectives in the analysis of ancient material. But most importantly, it shows the technology behind ancient cheese-making," Germany team leader Andrej Shevchenko, an analytical chemist at Germany's Max Planck Institute of Molecular Cell Biology and Genetics, told Discovery News.
Indeed, the analysis revealed Xiaohe's cheese wasn't made with rennet, an chymosine containing enzyme complex from calf intestine which was widely used since ancient times for curdling ruminant milk.
It was instead produced by combining milk with a mix of Lactobacillus kefiranofaciens and other lactic acid bacteria and yeasts.
The technique is still used today to make kefir cheese, similar to cottage cheese, and a kefir probiotic lactose-free beverage, food with a slightly sour taste first mentioned by Marco Polo in 13th century.
"It's the earliest known dairy practice that persists until present times in an almost unchanged way. The discovery moves the mysterious history of kefir as far as to the second millennium B.C., making it the oldest known dairy fermentation method," archaeologist Yimin Yang at the University of Chinese Academy of Sciences, Beijing, told Discovery News.
Edible for the lactose-intolerant inhabitants of Asia, the mummies' cheese was very simple to make. Kefir fermentation did not require slaughtering the livestock to obtain the curdling enzyme.
Furthermore, milk fat might have been physically removed in kefir cheese production, as now is commonly practiced in rural areas across the Eurasia steppe and also in Tibet.
"It's the first direct evidence that milking spread to Eastern Eurasia," Wang said.
Kefir production could have been scaled up or down according to the actual demand: dried kefir starter grains can be stored for years without losing their fermentation capacity. Fermented milk could be either consumed as a probiotic beverage or curdled protein mass strained into a cheese with extended shelf life and high nutrition value.
"This is a technology with the potential for mass production. It could have changed the nutritional habits of ancient populations of Eastern Eurasia," Andrej Shevchenko said.