Note: in the current (2015) BJCP Style Guidelines, Porters are in Category 13 Brown British Beer.
Here are some common questions many people ask about the Porter beer style:
What is a porter, what is the difference between a stout and a porter, what is a stout beer, or stout vs porter...Hopefully the information below will clear up these questions.
Porter is one of the beer styles in which many beer enthusiasts know its history. It is well documented in books and online. There is some controversy, however, as to the authenticity of some of its published history.
Most of the controversy comes from the most widely quoted source by a writer named John Feltham. In 1802 he wrote about the history of the style and based it on a letter written by Obadiah Poundage, a pen-name for a London brewer in the 1760's who wrote a letter in the London Chronicle arguing for an increase in the price of beer.
It seems that Feltham was unfamiliar with the brewing terminology of the 18th century, and probably misinterpreted some of the text. Feltham claimed that a brewer named Harwood made one beer which "simulated" the flavors of a blend of three different beers (brown or pale ale, mild ale and "stale" or well-aged and matured ale, often called Three Threads).
The new beer was called Entire, or Entire Butt, which would have meant "the entire barrel" or in American terms, "everything but the kitchen sink". One problem with this account is that no other writer before Feltham has ever said that the new Entire or Porter, was made to replicate the "three threads".
It seems more likely that the Porter beer style is just an evolution of the brown beers that were already being made in England for centuries.
Prior to 1700, most brewers in London would brew and then send out their green beer to be aged by the publican or dealers. But tastes changed, and Porter became the first beer to be aged in the brewery.
And with the industrial revolution at hand, it was the first beer that was made on a large scale. Several brewers made fortunes.
Up until around 1800, all London Porter was aged in large (really gigantic) vats for between 6 to 18 months before being siphoned to smaller casks for delivery to the pubs.
The demand soon began to outstrip the supply. Some enterprising publicans found that they didn't have to use all "aged" beer in their pours. They could mix the highly matured beer with two parts fresh or "mild" porter to produce a beer of very similar flavor to that of the "aged" beer.
As time wore on in the 19th century, tastes again changed and the style was more often sold "mild". Many discontinued making it all together as lagers and pale ales took their place in the brewery.
Porters were made entirely out of brown malt prior to the advent of hydrometers and thermometers.
Once the hydrometer began being used by the brewers, they quickly noticed that brown malt would yield only about 2/3 as much fermentable sugar as pale malt. And with higher taxation to pay for the Napoleonic War, brewers had an incentive to use less malt.
London brewers soon began mixing pale and brown malts to increase yield and profits. But in 1816 England passed a purity law which allowed only malt and hops in the beers sold there.
It just happens that in 1817 Daniel Wheeler of Charles Street, Drury Lane designed and began using a roaster, similar to a coffee roaster, which would roast malt without burning it. He named the new malt "patent malt" or black patent.
Brewers could now use up to 95% pale malt and 5% patent malt to create a palatable product much cheaper than before.
Because of the huge popularity of the porter beer style, brewers made them in a variety of strengths. The beers with higher gravities were called "Stout Porters".
Of the stout porters being produced, the lightest, at around 1.066 OG were simply called Single Stout Porter, often designated by a single "X" on the label.
Double Stout Porter (of which Guinness is an example) came in at 1.072 OG and had two "XX" on the label.
The Triple Stout Porter came in at 1.078 OG and Imperial Stout Porter began at 1.095 