Bitter is a British term for a type of beer or pale ale. The expression first appeared in the UK in the early 19th century as part of the development and spread of pale ale.

Bitter belongs in the pale ale style grouping, though bitter does have a greater variety of strength, flavour and appearance than mainstream pale ale. A bitter can be dark amber, approaching a stout, or be very golden and delicate like a golden summer ale. It can also go under 3% abv as with Boys Bitter and as high as 7% with some premium or strong bitters. During the early to mid 20th century there were some regional preferences noted which may still be detected in the beers of some of the more established breweries. In Cornwall, Wales, North England and Scotland the preference was for sweeter, less hopped beer. In other areas, particularly Southeast England, the preference was for hoppy beers.

Sub-types of Bitter

British brewers have several loose names for variations in beer strength, such as IPA, best bitter, special bitter, extra special bitter, and premium bitter. There is no agreed and defined difference between an ordinary and a best bitter other than one particular brewery's best bitter will usually be stronger than its ordinary. And two groups of drinkers may mark differently the point at which a best bitter becomes a premium bitter. Hop levels will vary within each sub group, though there is a tendency for the hops in the session bitter group to be more noticeable.

Drinkers tend to loosely group the beers into:

• Session or Ordinary Bitter: Strength up to 4.1% abv. The majority of British beers with the name IPA will be found in this group. Though bearing the name IPA these session bitters are not strong or hoppy. This is the commonest strength of bitter sold in British pubs. According to the Statistical Handbook of the British Beer and Pub Association, it accounts for 16.9% of pub sales.
• Best or Regular Bitter: Strength between 4.2% and 4.7% abv. According to the Statistical Handbook of the British Beer and Pub Association, bitter above 4.2% abv accounts for just 2.9% of pub sales.
• Premium or Strong Bitter: Strength of 4.8% abv and over. Also known as extra special bitter, or ESB (in the USA only - ESB is a brand name in the UK).