DUBLIN (AP) -- Food quality officials said Thursday they have identified more horsemeat traces in beef burgers produced in Ireland and pinpointed the problem in an imported ingredient. Ireland's second-largest manufacturer of supermarket beef patties shut down its production line in response.
The Irish Agriculture Department said nine of 13 burgers analyzed Tuesday tested positive for horse DNA. In a potentially crucial finding, it said seven ingredients added to the product also were tested — and only one, imported from an unspecified European country, tested positive for horse DNA. It said the six Irish-produced ingredients did not contain any equine material.
"Identifying the source of the one (ingredient) contaminated is good news. We're getting there. The fact that the burgers were contaminated isn't a surprise, if an ingredient was positive," said Mike Gibney, director of the Institute of Food and Health at University College Dublin.
The processing plant at the center of the controversy, Silvercrest Foods in the Irish border county of Monaghan, announced it would suspend operations indefinitely pending further investigations into why horsemeat keeps getting into its products. The company already has recalled around 10 million beef burgers from supermarket shelves here and its main export market, Britain.
Ireland ordered the fresh testing of Silvercrest burgers hours after the country's Food Safety Authority published test results Tuesday of 27 brands of beef burgers on sale in November and December at Irish supermarkets. It found horsemeat in 10 of them. While virtually all had only minuscule traces, one produced for British supermarket giant Tesco had 29 percent horse content in its meat.
While that discovery poses no threat to public health — horsemeat is on the menu in some European and Asian countries — Ireland says it highlights either sloppy practices, fraud or both in the production of processed meat products.
Gibney said supermarkets' focus on selling food at the cheapest possible price could be part of the problem. Beef is three to four times as expensive as horsemeat, which is primarily used in pet food.
"As you push down the price of the producer, they push down the price of their supplier, there you get into the danger," he said. "You might find a supplier cutting costs and putting ingredients in there that shouldn't be in there."
Tesco published large apologies in Irish and British newspapers Thursday, saying customers had a right to know exactly what they were eating.
Thursday's Irish government statement said the newly tested burgers from different production runs were made from Jan. 3 to Jan. 14. It offered no specifics on the levels of horse DNA detected in any of the burgers or the seven ingredients, saying these measurements would be made after further tests at a lab in Germany.
Department of Agriculture spokeswoman Martina Kearney said the government could not disclose the ingredient or its manufacturer, but said it came from a specific European Union country.
On Tuesday the Food Safety Authority said imported ingredients from both Spain and the Netherlands were suspected of causing the problem. Agriculture Minister Simon Coveney described the ingredient as a powdered beef-protein additive used to bulk up cheaply produced burgers with relatively little meat.
Silvercrest's parent company, ABP Food Group, says it will introduce DNA testing in its production lines and dispatched investigators to the production plants of all of its ingredient suppliers.
Such DNA testing is not yet widely used in the food industry. Ireland began the practice only in 2011, when it discovered that many of the fish labeled as cod in supermarkets and fast-food joints was actually more cheaply sourced whitefish such as Pollock. The DNA testing can establish the species of the meat, a question of honest food labeling, but generally has no health implications.
The original tests found traces of pork in most of the "beef" burgers too. Experts said this suggested that butchered beef may pick up airborne molecules of other slaughtered meats while being carried in refrigerated trucks or stored in facilities that handle other kinds of meat. But Silvercrest does not handle horsemeat, adding to the mystery.