Reminds me of the Johnny Appleseed story -- e.g., a lot of Americans grow up learning that he traveled far ahead of the settlers in North America planting apple seeds everywhere, so everyone would have apples -- the interesting twist is that apples planted from seeds aren't normally edible... but they can be used to make hard cider.
Medieval monks drank beer with breakfast before their pre-dawn prayers, hence the robust brewing tradition in monasteries. Essentially, our ancestors ground whatever grain they could get their hands on, mixed it with some water, slapped it on a greased, hot rock and called it breakfast.
Site is down at the moment so I can't RTFA, but I remember my brother-in-law (PhD religious studies, Oxford) telling me this in 1997. So it ain't new news.
Old beer was pretty much liquid bread very thick to the point of making Guinness seem like water and very nutritious.
The amount of alcohol was most likely quite low 2-3% and you could easily decrease it by heating the beer.
Fermentation was most likely an unexpected or even undesirable outcome of saccharification since we can't digest starch that well.
Because saccharification of starch requires an enzyme which is usually gained from malting the grain you can't really avoid fermentation especially in the pretty unsterile conditions of the Stone Age.
Probably quite close if you want to recreate it I mix a thick stout like Guinness with something like semolina or wheat middlings or maybe groat and boil it, won't taste good but it sure will fill a man.
Beer has very low caloric value a pint has on average 150 kcal or so, so you need something much more nutritious than that (500-800 kcal per serving) to make it worth your while, especially when you were living in a time where your daily caloric expenditure could be easily twice what is today.
Keep in mind medieval beer was quite low in alcohol, and brewing it was meant more to purify questionable water than because everyone wanted to get wasted all the time (although it's easy to develop that sort of mental picture.)
