In-house tampering is being blamed for GNP Co. of central Minnesota recalling more than 27 tons of chicken over the weekend after contaminants were detected in some of the product that was distributed primarily to food service and institutional outlets.

The recall involving the Gold’n Plump and Just Bare brands by the Upper Midwest’s leading chicken manufacturer follows the company disclosing the discovery of sand and black soil in the chicken. GNP is the parent of the popular Gold’n Plump brand.

“Our own inspections turned it up,” said Lexann Reischl, a GNP spokeswoman, “and two food service customers called and told us they found the same material.”

In a statement issued Sunday afternoon, the company said, “Extraneous foreign matter … is linked to an isolated product tampering incident that occurred at the company’s Cold Spring processing plant the week of June 6.”

An employee, who has since been fired, is believed to be behind the contamination, Reischl said.

Cold Spring Police Sgt. Jason Blum said Sunday “there is a known suspect” being investigated, but an arrest has not been made.