Take home message

• Why bury dead people with kefir grains?
• Mummies from the Chinese Xiahoe cemetery in Xinjiang district wore a necklace of SCOBY (grains) around their necks 3,500 years ago (Bronze Age). Were people buried with relics of value to them or in their culture?
• For such a lactose-intolerant population, kefir grains are important because by adding the grains to milk, now one could digest the milk properly. Perhaps there was also a belief in an afterlife, and people gave such grains to the deceased. Otherwise, it surely came in handy in an afterlife.

A mummy about 3,500 years old from the Xiahoe cemetery in China. The red arrows point to the kefir grains lying around the neck like a chain (taken from Liu et al., 2024)

Lactose conversion

SCOBY we know as kefir grains. Chinese researchers (Liu et al., 2024) call it ‘kefir cheese’. In any case, it is the starter, the complex of bacteria and fungi that ferments (raw) milk into a longer-lasting product. Moreover, and of great importance to Asians, fermented products could be digested without the possession of the enzyme lactase. Asians, Chinese, Mongolians, Tibetans, although known for the consumtion of milk products (sheep, goat, yak, horse), are lactose intolerant. Their adaptation to still be able to consume milk is a cultural adaptation, namely by fermenting the milk with kefir grains.

Sifted and washed kefir grains after making kefir drink within 24-36 hours

Without lactic acid fermenting bacteria, it was impossible to ferment the milk, and make it last longer as yoghurt, kefir drink, fresh cheeses, Gouda cheese or mountain cheese. Early milk processors used various methods to acidify milk, such as kefir grains or wooden milking tools or administering acidified whey to the fresh milk. The peculiarity of both kefir grains and wooden vessels is that they act as coat hangers for lactic acid bacteria. These places hide inside and on the grains, as well as in the cracks, crevices, fissures of the wood.

Wooden cheese tools as a starter are still used successfully, which is excellent if you make the warm milk (from a single milk meal) into a cheese twice a day (morning milk separately, evening milk separately). For centuries, Dutch farmers in the meadow area made their Gouda cheese this way. In other regions of Europe, too, wooden cheese vats were and still are used to process cheese milk in the traditional way. Sun and D’Amico (2023) name 7 different European cheeses where a wooden cheese vat is significant, including in the French Salers or the Italian (rather Sicilian) Pecorino. Funnily enough, here too, as in kefir grains, Lactococcus lactis strains, but also the Lactobacillus kefiranofaciens play an important role as starter, now from the cracks in the wood. We described earlier, how these authors show in a very insightful way, how the starter culture nestling in the wood, ultimately determines the fermentation of the cheese milk.

Traditional wooden cheese vat, the Tina from Italy

Kefir originates from the Caucasus

It remains unclear, how and when exactly the kefir grains were composed, in which lactic acid-digesting bacteria plus yeasts live. The grains or SCOBY form an ecosystem in their own way. SCOBY did not exist until many millennia later, after the domestication of our farm animals and the first milk processing started. How and since when kefir was deployed on the steppes in Mongolia is also unclear. Between the start of animal husbandry some 10,000 years ago and the mummies in China, there is a period of more than 6,000 years. The Chinese research does still show, however, that there are differences between Tibetan kefir on the one hand and Caucasian and European kefir on the other. Different strains of Lactobacillus kefiranofaciens have been found in the regions. They are likely to be adaptations in the genome, created by environmental differences. However, the similarities between the kefir from the two regions outweigh the differences. Even in wooden cheese vats the same bacteria are found, now not trapped in the kefir grains, but in the wooden walls and cracks of the cheese vat, even wooden vats and kefir grains look alike. They are the carriers of the leaven, the starter of the fermentation of milk sugar into lactic acid. The wooden barrel and grains of kefir as biofilm are necessary for making any type of dairy (fresh cheese, yoghurt, hard cheese, mould cheese, ….).

Literature

• Liu, Y., Miao, B., Li, W., Hu, X., Bai, F., Abuduresule, Y., … & Fu, Q. (2024). Bronze Age cheese reveals human-Lactobacillus interactions over evolutionary history. Cell, 187(21), 5891-5900.

• Sun, L., & D’Amico, D. J. (2023). The impact of environmental conditions and milk type on microbial communities of wooden vats and cheeses produced therein. Food Microbiology, 115, 104319. https://doi.org/10.1016/j.fm.2023.104319