HONG KONG — When the 3,600-year-old coffin of a young woman was excavated in northwestern China two decades ago, archeologists discovered a mysterious substance laid out along her neck like a piece of jewelry.

It was made of cheese, and scientists now say it’s the oldest cheese ever found.

“Regular cheese is soft. This is not. It has now become really dry, dense and hard dust,” said Fu Qiaomei, a paleogeneticist at the Chinese Academy of Sciences in Beijing and the co-author of a study…