Bitters, Best Bitters, ESB, Amber & Red Ales – These were developed towards the end of the 19th century and grew from pale ale which was usually deep amber to copper in colour. This was due to the use of slightly darker crystal malts that give the beer a fullness of palate.
Over time brewers began to produce ‘running beers’, which could be served in pubs after only a few days storage as brewer’s moved away from vatted beers which had to be stored for many months. Bitter as we know it today is very much different to 19th century "bitter ale". Over the course of time between then and now, taxation has had a significant impact on british brewing and in the 19th century, bitter was brewed a far stronger beer than it is today. An average bitter today has a ABV strength of 2.5% to 3.9%. Best bitters have a strength of 4% upwards whilst extra or strong bitters 5% or more.