tdbcelts.org

I don't know how factual it is, but it seems to be a theory that works. The grassy mounds known as a fulacht fiadh might have been used to brew ale.

http://www.wired.com/culture/lifestyle/ ... 12/ps_ale/

Here's the most relevant bits to us:

Quinn and Moore got a crash course in ancient techniques by visiting breweries in Spain, Belgium, and Canada. Then they repurposed a cattle trough, filling it with water and placing it in a clay-lined hole. Using granite stones toasted in a nearby fire, the pair heated the water until it was steaming but not bubbling — according to the brewers they consulted, 153 degrees Fahrenheit is the ideal temperature for breaking down starch into sugar. Then they scooped in barley. After bringing the concoction to a boil, they transferred it to containers, added bog myrtle, meadow sweet, and, of course, yeast — all ingredients available to Bronze Age boozers. Three days later, the slightly fizzy copper-colored ale was ready for consumption.

Can I get some bog myrtle and meadow sweet at Stop and Shop?

Here's a link to the group that did this experiment: Moore Group. They have pictures too. This was posted to Norseland's Yahoo group awhile back.