Hops. Ale doesn't have hops in it. Centuries ago ale was drunk in the UK coz we didn't have hops here. In the 15th century Dutch merchants started coming to the UK in larger numbers than ever before and bought beer and hops with them. We readily embraced beer drinking and started brewing our own. So technically speaking ale doesn't exist any more - if ale has hops in it then it's beer - beer has hops in it coz it's beer, so what's the difference?