Bitters developed towards the end of the 19th century as brewers began to produce beers that could be served in pubs after only a few days storage in cellars. Bitters grew out of pale ale but are usually deep bronze to copper in colour due to the use of slightly darker crystal malts. Varying in flavours from medium to deep, full-bodied bitterness, bitters range in strength from under 3% to as high as 7% ABV in premium and strong bitters.