The tradition of using bogs to keep butter edible dates back over 3,500 years, according to a new study.
It reveals the practice dates back to at least 1750 BC, a further 1,500 years than was previously thought.
The study was carried out by scientists and archaeologists at University College Dublin , Queen’s University, University College Cork , the University of Bristol and the National Museum of Ireland .
The bog’s preservative powers are so strong that butter can still be edible after centuries in the ground, according to the group.
“The cool, low-oxygen, high-acid environment of the bog means it was ideal for preserving perishable food before modern refrigeration,” they said.
Prof Richard Evershed , from the University of Bristol said: “The widespread occurrence of these enigmatic butter deposits fits with our increasing knowledge of the central importance of dairying in prehistoric northern Europe . ”
Four of the five Bronze Age bog butters studied by the team came from Co Offaly – two were found near at Ballindown and Drinagh , while the other two examples were discovered approximately 12km apart at Esker More and Knockdrin.
The fifth was received from Clonava in Co Westmeath. The earliest dated sample from Knockdrin dates from between 1745-1635 BC.
Dr Jessica Smyth from the UCD school of archaeology said: “Clearly, it is unlikely there was a single reason for the deposition of bog butter over four millennia.
“In certain periods they may have been votive deposits, while at other points in time it may have been more about storage and even protection of valuable resources.”
Isabella Mulhall , curator at the National Museum of Ireland said: “Each year the National Museum of Ireland works with Bord Na Móna and with private individuals to record and retrieve bog butters that are found by chance.
“The Museum is particularly grateful to finders throughout the country who take the time to report these important finds and allow us to protect them for future research such as that featured here.”