Beer in 5th century Britain

Brewing in Britain was probably well established when the Romans arrived in 54 BC,[1] and certainly continued under them.

"In the 1980s archaeologists found the evidence that Rome's soldiers in Britain sustained themselves on Celtic ale. A series of domestic and military accounts written on wooden tablets were dug up at the Roman fort of Vindolanda, at Chesterholm in modern Northumbria, dating to between AD90 and AD130. They reveal the garrison at Vindolanda buying ceruese, or beer, as the legions doubtless did throughout the rest of Roman Britain, almost certainly from brewers in the local area."

"One list of accounts from Vindolanda mentions Atrectus the brewer (Atrectus ceruesar[ius), the first named brewer in British history, as well as the first known professional brewer in Britain. The accounts also show purchases of bracis or braces, that is, emmer wheat (or malt), doubtless for brewing. Quite possibly the garrison bought the malt, and hired a local brewer to make beer from it for the troops."

"In Roman Britain, brewing, both domestic and retail, must have been widespread: remains indicating the existence of Roman-era malting or brewing operations have been found from Somerset to Northumberland, and South Wales to Colchester. In the third and fourth centuries AD Roman hypocaust technology, for supplying central heating to homes, was adapted in Britain to build permanent corn dryers/maltings, and the remains of these double-floored buildings, with underground flues, are found in Roman towns
as well as on Roman farms."[2]

British brewing is generally thought to have been part of a wider Celtic tradition. Since this was well before the introduction of hops, other flavourings such as honey, meadowsweet and mugwort may have been used

Wiki - Romano Celtic Britain