Used to describe ones facial expression of disgust and dislike. Rather like the expression one would pull if they began chewing on a whole lemon. It is typified by an indescribable mouth shape. This expression is commonly used in Northern Ireland, where the world Bake is used in reference to ones mouth.
The 'sour bake' is measured on the 'sherbet lemon scale' created by the notorious genious, The Commodore. On this scale, the intensity (e.g. level of disgust) with which a sour bake is pulled is proportional to the equivalent face which would pulled if that person were sucking on a certain number of sherbet lemons. For example, a particularly strong sour bake would be equivalent to sucking on approximately 10 sherbet lemons at once. Therefore, it would be rated as 10 on the sherbet lemon scale.
In working class areas of Belfast sour bake dueling is a very popular sport amoung the elderly female population, commonly referred to as old hags or aul dolls. This sport involves standing on street corners gossiping while seeing who can pull the sourest bake in response to a particular incident with which they are not best pleased about e.g. local yobs graffiting a house with a sexually explict drawing.
Trivia: the greatest sour bake ever recorded was on the Shankill Road, Northern Ireland on July 17th 1986 with a sour bake rating of 18.9 sherbet lemons.
Doris Morris (standing on street corner): Would you look at the state of that young hussy (pulls a sour bake)
Jemima Puddleduck(friend of Dorris): A disgrace
Innocent nerdish bypasser: Look at the SOUR BAKE on her
Innocent nerdish bypasser too: Ha, she has some SOUR BAKE, equivalent to 7 sherbet lemons I would say!