I can't speak for wine or mead, but with beer it is very difficult to know. In fact, anything prior to the late 18th century would be speculative at best. The reason is that there are no analyses of the beers and very few recipes that have survived. And even if you had the recipe, you'd be speculating. Grain cultivars used for brewing (barley was only one among several, oats, wheat and rye where also popular) and malting methods have changed a lot since the Middle Ages and we don't know the yield the malts had, what temperatures they mashed at or the attenuation levels that could be expected from the yeasts.

Chances are, however, that they were weaker and thicker than your average beer today, and far more acidic. They also were drunk younger than it is common today. The Ales brewed in England that would eventually evolve into Mild were served shortly after primary fermentation was done.