Beer is a drink that dates back to the ancient civilizations of Mesopotamia and Egypt. In its earliest forms, it was made from grains, or bread, which were allowed to ferment and liquefy. Hence, its alter-ego "liquid bread". Over time the process evolved, with most Europeans settling on barley and wheat as their grains of choice and flavorings introduced with the addition of "grut", a mixture of herbs that varied from brewer to brewer. Hops came next, adding flavor and acting as a preservative and eventually replaced grut as the primary flavoring agent.

The next evolution in the brewing was the shift from top-fermenting yeast, a successful process when a relatively warm climate, typical of the Ireland and Britain, allowed fermentation to take place at room temperature. In colder climates, such as German areas of continental Europe, bottom-fermenting yeast proved more successful for fermentation. The result was a split between the ales (of which stout is but one type), popular in Ireland and Britain, and lagers, popular in German regions.

Stout originally was a beer called porter, named after the porters of the London docks who first favored the drink. Its roots however, may be found in a blended concoction known as "three threads." A bartender would mix equal parts of young and old brown ale and pale ale—the last also known as "two-penny" because of its high price. This popular drink blended the complexities of old ale, the cleaner taste of the pricier pale ale and the balance of the affordable young brown. But it was complicated for a busy bartender to prepare. So in 1722 a brewer named Ralph Harwood copied the taste of the mix and developed a single beer, the world's first porter. This was called "entire," because the beer was brewed in one vessel instead of three.

Irish brewers came to use roasted barley for their ales and stout became a national preference. It is opaque ale, almost black in color and with a creamy head. Ingredients vary with the brewer but generally include dark roasted barley, which contributes a slightly roasted character and hops with a medium-to-high bitterness.

Beamish & Crawford, which began brewing in Cork as the Cork Porter Brewery in 1792, was the largest brewery in Ireland in 1805 when they produced 100,000 barrels of suds.

Murphy Brewery Ireland, established in 1856, also in Cork, initially produced brands known as Lady's Well Ale and Murphy's Porter, which was lighter than stout, but similar in its use of roasted barley. They entered the stout market in Ireland in 1889 but it was almost 100 years before the Murphy's Irish Stout was exported. Its current parent, Heineken International, acquired Murphy's in 1983.

Guinness was established at St. James Gate, Dublin, in 1759. Within a decade they were exporting porter to England and had essentially removed imports from the Irish market. By 1799, ales were no longer on the menu - Guinness brewed only stout. They overtook other breweries to become the largest in Ireland by 1833 and the largest in the world by 1886.

This is interesting:

At 198 calories, a pint of stout has fewer calories than a pint of skim milk or orange juice.

Around 13 million glasses of stout are consumed around the world every day.