In the late 1990s, archaeologists working in the arid Tarim Basin, in the middle of China’s Xinjiang region, excavated hundreds of boat-shaped coffins dating back to the Bronze Age, about 3500 years ago. When researchers opened the wooden vessels and unwrapped the cloth-covered bundles inside, they came face to face with a surprising sight: mummies warmly clad for the afterlife in tall, felt hats and woven wool garments, with ghostly white faces. Some had bumpy, cauliflowerlike beige lumps strung around their necks.

The mummies buried in the Xiaohe Cemetery, it turns out, were covered in cheese…

Variants of both bacteria are still found in modern kefir, a fermented dairy drink that can be strained to make a kind of soft cheese, produced across Europe and Asia. “It’s the oldest cheese DNA in the world,” Fu says.

The lumps were probably kefir starter grains, the concentrated bacterial colonies used to start fermentation in new batches of cheese—a precious gift to take into the next world.

The kefir was part of a remarkably cosmopolitan diet for the Xiaohe people. Previous studies of their dental calculus showed they ate dairy and wheat from western Asia, millet grain from eastern China, and medicinal plants sourced from hundreds of kilometers away.