Filler ingredient from Poland is the source of horse DNA found in beef burgers on sale in the UK and Ireland, according to Irish agriculture officials.

Fresh tests on the suspected Polish ingredient have shown up to 20% horse DNA content relative to beef, Ireland’s agriculture ministry said at the weekend. This confirms earlier tests that pointed to Poland as the source of the horse DNA in beef burgers.

It has taken ten days of intense investigation by UK and Irish food safety officials to track down the source of the horse DNA, which has led to recalls by Tesco, Aldi, Lidl and Iceland, as well as “precautionary” recalls by Sainsbury’s, Asda and Waitrose. 

However, the Poland-based ingredient producer’s identity remains unclear. APB Food, which has seen two of its processing facilities as the centre of the horse scandal, denied over the weekend that its own plant in Poland had any involvement.

“The source of the contaminated meat from Poland is not related to ABP’s plant in Poznan,” said the firm. “As with all other parts of the Group this plant does not process any horse meat.” 

In addition, the source of pig DNA found in several beef ready meal products remains unclear. In the UK, the Food Standards Agency is conducting DNA tests across the meat supply chain to understand the extent of undeclared meat in products. 

Late last week, Tesco was forced into a fresh investigation after it emerged one of its stores in the UK overrode a recall notice to sell withdrawn beef burgers to a BBC journalist.

Since the scandal broke, further tests on the key suppliers involved – APB Food and Liffey Meats – show no new cases of horse DNA in their products. APB has introduced DNA testing on meat, “over and above any legal requirements”, it said at the weekend.

The processor’s CEO, Paul Finnerty, apologised for “the impact this issue has caused”. He added that, since the issue became public, APB has restructured its business, putting its Silvercreat plant within APB Ireland and Dalepak in APB UK.