Was beer really weaker in the past?

Beer is one of the oldest and most widely consumed drinks, with profound social, economic and cultural significance in human history. It is commonly believed that, particularly in medieval times, weak (low-alcohol) beer was consumed in vast quantities because it was safer to drink than water, which was often contaminated. Since then, the story goes, the alcohol content has increased - but how true is this?

- Fergus Collins

The earliest evidence of brewing comes from Sumerian clay tablets made in Mesopotamia - in what is now Iraq - around 4000BCE. Beer was also produced in huge quantities in ancient Egypt, Greece and Rome.

Beer is produced when malt sugars extracted from grains such as barley interact with yeasts to create alcohol. The process has been refined over time by careful malt extraction, cultivation of the most effective yeasts and the addition of hops, for a rounded, bitter flavour and to act as a preservative.