Guinness is a popular Irish dry stout that originated in the brewery of Arthur Guinness (1725–1803) at St. James’s Gate, Dublin. Guinness is one of the most successful beer brands worldwide. It is brewed in almost 50 countries and is available in over 100. 1,800,000,000 US pints (850,000 m³) are sold annually.

A distinctive feature is the burnt flavour that is derived from roasted unmalted barley (though this is a relatively modern development since it did not become a part of the grist until well into the 20th century). For many years a portion of aged brew was blended with freshly brewed product to give a sharp lactic flavour. Although the Guinness palate still features a characteristic “tang”, the company has refused to confirm whether this type of blending still occurs. The beer’s thick, creamy head comes from mixing the beer with nitrogen when poured. It is popular with Irish people both in Ireland and abroad, and, in spite of a decline in consumption since 2001, is still the best-selling alcoholic drink in Ireland where Guinness & Co. makes almost €2 billion annually.

The company had its headquarters in London from 1932 onwards. It merged with Grand Metropolitan plc in 1997 and then figured in the development of the multi-national alcohol conglomerate Diageo.

Info gleaned from Wikipedia