While France may be best-known for its wines these days, in the Iron Age, they were making plenty of beer—and now we have a reasonably good idea of what that process looked like (at least for one archaeological site).
The site of Roquepertuse lies in Provence, just inland from France's southeastern Mediterranean coast. From the Late Bronze Age (c. 1400-750 BC) to the Late Iron Age (c. 450-25 BC), the local inhabitants cultivated barley, as well as millet and emmer—all grains used in ancient beer brewing, although of course barley is the most recognizable to us today.
When originally discovered in the 19th century, Roquepertuse was thought to be a Celtic religious center (or 'sanctuary'—when in doubt, archaeologists always invoke 'ritual' to explain just about everything), thanks to some impressive statuary found at the site, but more recent excavation and analysis points to a more prosaic village settlement (albeit one that was violently destroyed on more than one occasion over its time 'in operation').
But what is especially interesting about Roquepertuse is that the its Iron Age residents were not just growing barley—and by this point, it was already domestic barley, not the wild variety—but they were malting it.
Before diving into the archaeology, a little background on basic brewing may be useful. The barley found at the site was six-row barley; the number refers to the arrangement of the grains on the plant. While many brewers now prefer two-row barley because of its higher starch content, six-row barley is still widely used, especially by larger commercial breweries. Barley on its own won't magically become beer, however—it needs to be malted first, and the resulting malt is what is used to make beer. The malting process involves steeping the grain in water and allowing it to germinate, and then drying the malt; nowadays, the drying portion of the process typically takes place in a kiln.
It seems that things were not so different in Celtic France, albeit on a thoroughly domestic scale—today's locavores would be thrilled by the fact that everything needed to make the beer was grown or processed within walking distance of the site, much of it within the likely dwelling space.
The key to the Roquepertuse site is the oven, discovered just two meters from a large concentration of germinated, carbonized barley, essentially in the next room. It's likely that the barley was soaked in one part of the building, then dried in the oven. The malt was probably much smokier than most are today, given the limitations of Iron Age ovens, but that was not the only difference from modern beer. The brewing process likely included ingredients beyond this carefully-malted barley—bog myrtle has also turned up in archaeobotany analyses from Iron Age Germany (and, indeed, was used commonly through the Middle Ages as well), and it's possible it was a common additive in contemporary European beer, along with potentially mind-altering substances like henbane.
Beginning around 500 BC, evidence for grape vines becomes more pronounced in the region, but most archaeologists agree that wine-drinking and production was brought to France and Spain from the eastern Mediterranean by Greeks and Phoenicians—beer was the native drink long before wine caught on.
We know from other evidence that beer was a very visible part of Iron Age culture across much of Europe—drinking horns, cauldrons, cups and the like appear everywhere from high-status graves to (wait for it) ritual deposits. A few centuries later, Greek and Roman writers noted varieties of Celtic beer and mead (typically in a disapproving context, at least in relation to wine)—corma, made from wheat and honey; zythos, from barley and honey; cervesius, derived from unnamed grains, and barley-specific beer in southeastern France known (to the observers) as krithinon poma.
Some Celtic tribes even forbade the importation of wine—most notably the Germanic Suebi and the Belgic Nervii—something that baffled Julius Caesar in his Commentarii de Bello Gallico, although given Belgian and German beer cultures today, perhaps that is not surprising. Even Pliny the Elder remarked on long 'shelf-life' some Celtic beers were rumored to have, long before his namesake beer was dreamed of:
The nations of the West have their own intoxicant made from grain soaked in water; there are a number of ways of making it in the various provinces of Gaul and Spain and under different names though the principle is the same. The Spanish provinces have by this time even taught us that these liquors will bear being kept a long time.
While it is unlikely Pliny thought of Celtic beer as potentially lasting quite this long, certain basic elements of early European brewing still survive—future research should continue to highlight other aspects of ancient beer we're missing out on (or, perhaps, are lucky to be avoiding) today.