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.

The recall is categorized as "high," the most serious level applied by regulators with the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS). The agency's recall announcement Saturday noted that no illnesses have been reported in connection with the 55,608 pounds of chicken being recalled.

The company statement noted that a third-party lab "verified the foreign matter to be benign, natural materials. … However, because the company cannot say with 100 percent certainty that the product is safe for consumption," the recall was required.

The chicken produced by St. Cloud-based GNP, whose Gold'n Plump brand is a staple in Minnesota supermarkets, was produced from June 6-9 and packaged in 40-pound cases for food service and retail distribution, the FSIS said.

The products bear "P-322" inside the USDA mark of inspection.

Only one of the products being recalled is sold in grocery stores, that being the Just Bare 4-pound whole chicken with the same inspection mark and the use-by date of June 26. Its UPC is 024105594057.

"Consumers who have purchased these products are urged not to consume them," the federal recall notice read. The products should be discarded or returned to where they were bought for a refund, the notice added.

Consumers with questions about the recall can contact GNP's Jane Kalthoff at 1-800-328-2838.

For further details on the products being recalled, visit: tinyurl.com/hspq67m.

GNP has two plants that slaughter birds and produce finished chicken products — in Cold Spring and Arcadia, Wis. — and a third facility in Luverne, Minn. It also owns four hatcheries and feed mills and employs more than 1,700 people.