Beer style is a term used to differentiate and categorize beers by factors such as colour, flavour, strength, ingredients, production method, recipe, history, or origin.The modern concept of beer style is largely based on the work of writer Michael Jackson in his 1977 book The World Guide To Beer in which he categorised beers from around the world into style groups according to local customs and names. In 1989, Fred Eckhardt furthered Jackson's work publishing The Essentials of Beer Style.