Hans Hallén, who monitored ICA stores in southern Sweden from 2003-2005, said he had informed the company's managers of the exact practices that were exposed in an investigative television programme earlier this week.
According to Hallén, many stores engaged in practices such as repackaging meat in order to change the best before date.
"They even re-minced meat that had already been out on the shelves, before repackaging it and putting it back out on the shelves," he told Sydsvenskan.
Sausage meats that had become old and sticky were also repackaged after rinsing, he said.
Hans Hallén was one of eight quality control managers employed by ICA until 2005, when the position was discontinued.
"Our main job was to train staff in order to ensure that scandals of this kind would not occur," he told Sydsvenskan.