( CNN ) -- The discovery of horse DNA in hamburgers on sale at supermarkets in Ireland and Britain is testing the appetite of meat lovers there . The Food Safety Authority of Ireland said Tuesday that 10 out of 27 hamburger products it analyzed in a study were found to contain horse DNA , and 23 of them tested positive for pig DNA . Read more : Multi-state beef recall tied to potential E. coli contamination . The horse-tainted burgers , on sale at several different supermarket chains , came from two meat processing plants in Ireland and one in Britain , the Irish authority said . `` This raises concerns in relation to the traceability of meat ingredients and products entering the food chain , '' it said , but noted that the findings posed no risk to public health . Read more : Bacteria seen in nearly half of U.S. meat . In nine out of the 10 burger samples , the horse DNA was found at very low levels , the authority said , but in one sample from Tesco , Britain 's largest retailer , the horsemeat accounted for about 29 % of the burger . Tesco responded by pulling from its shelves all products from the company that had supplied the dubious burgers . Read more : How severe weather makes people go hungry . `` We understand that many of our customers will be concerned by this news , and we apologize sincerely for any distress , '' Tesco said . The retailer is working with Irish and British authorities and the supplier to work out what had happened , it said . Alan Reilly , the chief executive of the Irish food authority , said there was a `` plausible explanation '' for the pig meat finding its way into the burgers , since meat from different animals is processed at the same plants . But he said there was `` no clear explanation at this time '' for the presence of the horsemeat . Report : Unsafe food putting lives at risk . `` In Ireland , it is not in our culture to eat horsemeat and therefore , we do not expect to find it in a burger , '' Reilly said . `` Likewise , for some religious groups or people who abstain from eating pig meat , the presence of traces of pig DNA is unacceptable . '' Many British and Irish people expressed their distaste over the revelations on social media . Read more : Horse -- coming soon to a meat case near you ? Some Twitter users said they were n't surprised to hear about the questionable origins of the burgers , while others debated the ethics of eating horsemeat . And then there were those who saw an opportunity for attempts at humor . `` Going to # tesco and expecting a beef burger . Instead you get # horsemeat . Sounds to me like foal-play , '' wrote Twitter user Matt Oswin under the username @ BrushmanLestar .
Irish Food Safety Authority finds horse DNA in 27 out of 10 burgers it tested . The hamburgers are on sale in supermarkets in Britain and Ireland . The agency finds about 29 % of a burger from Tesco to be made of horsemeat . Tesco says it has withdrawn from sale all products from the supplier in question .