Billy Quinn and Declan Moore, two archaeologists with Moore Archaeological & Environmental Services (Moore Group) in Galway, believe that an extensive brewing tradition existed in Ireland as far back as 2500 BC. In an article to be published in Archaeology Ireland next month, they detail their experiments and research into the enigmatic site that is the fulacht fiadh. These monuments (of which there are approx. 4500), which present in the landscape as small, horseshoe shaped grass covered mounds, have been conventionally thought of by archaeologists as ancient cooking spots. However, Quinn and Moore believe that they may have also been used as breweries.
On the one hand, beer was probably ubiquitous so this isn't very far fetched. OTOH, the admit it's all circumstantial and vaguely Kon Tiki-esque. Need something actually linking the sites to beer-brewing specifically.
There's a link to the beer project, too.