According to the Changsha Administration of Customs, one-third of the meat on sale at the largest wholesale market in the city was found to be illegally imported. While the origin of the smuggled meat was unclear, a report on the official Hunan propaganda department website said that the contraband had come from the border with Vietnam.

In the region of Guangxi, which borders Vietnam, customs officials found that some of the smuggled frozen meat “was more than 40 years old,” according to The China Daily newspaper. Chinese officials did not explain where the meat originated or how it had been stored for almost two generations. After being refrozen, the meat was sold to retailers, supermarkets and restaurants across the country. China Central Television, the state broadcaster, showed workers in the southern city of Shenzhen repackaging the imported meat with Chinese labels, even though imported products, if legal, tend to be more profitable.

Some of the meat was sold on the Internet. Many meat retailers have set up profiles on Taobao, the online shopping website owned by Alibaba, offering local and imported meat. Some claim to be selling beef imported from the United States, even though such beef has been barred from the Chinese mainland since 2003, after outbreaks of bovine spongiform encephalopathy, or mad cow disease.

Food scandals are a politically sensitive issue in China, where tainted food has sickened huge numbers of people. In 2008, milk powder tainted with melamine, a toxic industrial compound, made 300,000 babies ill and six died. Since then, the country has encountered watermelons that exploded from the misuse of a growth accelerator chemical, pork soaked in a detergent additive, steamed buns tainted with pesticides, and 15,000 dead pigs drifting down the Huangpu River in Shanghai.

But the news of 40-year-old frozen meat being sold to consumers has left even the most seasoned experts in shock. Bob Delmore, an expert on meat science at Colorado State University, said that although it was possible for meat to last that long frozen, it would be covered by “a tremendous amount of freezer burn” as the product lost moisture and the flesh degraded. But once it began to thaw, a consumer would immediately know something was wrong. “The dead giveaway would be the odor and the taste,” he said.