Today we raise a glass to International Stout Day and dedicate this blog to the age-old question of “What is the difference between stout and porter?

Though this question is yet to find a definitive answer, many historians have speculated on the origin of porter, and how this led to ‘stout’ as the style that we know and love today.

Porter is believed to have originated in 18th century London, when brewers were forced to create low-strength ales that were uncompromising in flavour, as taxation on malt was levied by the government (malt provides a brewer with fermentable sugars, dictating the strength of his/her beers).

Mad Squirrel Brewery’s ‘London Porter’

Increased hopping regimes and darker malts (chiefly brown malt) were employed in these weaker ales, as brewers looked to maximise their overall drinking appeal. These lower-strength beers were deep in colour with confectionary flavours and floral aromas, often matured in large oak vats, contributing additional notes of oak and vanilla (hops are antimicrobial, so increased hopping would have facilitated the extended ageing of a brew).

These luxurious dark ales won the favour of many a Londoner, no less the dockside workers that unloaded boats on the River Thames. Soon enough, loyal drinkers of the style inspire its’ namesake and ‘Porter’ as we know it was born.

As porter grew in popularity both fresh and aged, the dark style proved a prime product for export, with orders of ale brewed for long-haul shipping to the Baltic States. The brewers of London were keen to cater for this emerging market, adding new lines such as ‘Baltic Porter’ and ‘Russian Imperial Stout Porter’ to their portfolios – each using the ‘stout’ as an adjective for strong. In the form of an adjective, ‘stout’ could prefix any beer to denote a higher strength version its’ style, regardless of colour (pale, amber, dark or otherwise).

All of this begs the question that, if stout is just a reference of strength, then why do modern drinkers use the word to describe a specific style, a style that sets itself apart from traditional London Porter?

The answer is not a straightforward one, though a number of events are perceived to be key in the story of how stout and porter became two seperate entities.

The brewer’s hydrometer came into commercial use in Britain throughout the 1800s, measuring the diastatic efficiency of fermentable grains. This equipment led to the observation that pale malt was more fermentable than its’ darker counterparts, which had been kilned at higher temperatures for longer durations. As the industry learned that brown malt was not as efficient as pale malt, the idea of using brown malt alone for colour and flavour became less attractive for margin-conscious brewers.

Daniel Wheeler invented Black Patent Malt using his unique drum roaster in the year 1817. Black Patent Malt was a new style of grain that, even when used in small quantities, gave a jet-black colour to ales, with flavours of intense coffee and cocoa. This new variety of grain packed a punch and offered a perfect solution to brewers that were keen to maximise the diastatic efficiency of their dark beers. Not before long, brewers began trading off portions of brown malt in their grist for Black Patent Malt, using a pinch or two of this new, intensely dark ingredient.

Tea Kettle Stout from Tring Brewery

As sales of porter reached their Golden Age, many English brewers aired on the side of caution when altering their flagship beers, keeping brown malt in their recipes for fear of losing loyal drinkers. The loyalty of English drinkers was of no concern to Arthur Guinness, an apprentice brewer in London who, upon graduating, returned to his native city of Dublin to build Ireland’s most famous brewery.

Armed with a knowledge of diastatic efficiency, Arthur built his flagship dark ale with a base of pale and black malts only. This flagship beer was Guinness Stout Porter, a style defining beer with notes of rich coffee and dark chocolate, finishing with a dry palate and respectable bitterness.

As much a marketeer as he was a brewer, Arthur came to drop the word ‘porter’ from his product altogether and thus ‘Guinness Stout’ was born. As Guinness Stout grew into the global brand that it is today, so too did the idea that Irish Dry Stout symbolised everything that a London Porter wasn’t, dividing the timeline of the two styles thereafter.

Club Hammer Stout from Pope’s Yard

In a nutshell, porter is recognised today as a beer sweet in flavour, with notes of caramel and biscuit, deep brown in complexion with a well-rounded body. Conversely, stout is recognised as a more robust drink than porter, boasting a pitch-black complexion with roasty flavours, finishing dry and bitter on the palate.

So, there we have it – an abridged history of how porter came to be and how stout splintered away to become its’ very own style. There are still so many things that we don’t know about stout’s divergence from porter, but why let the nitty-gritty bog down our day of festivities?

Whichever style you’re drinking, raise a glass of the dark stuff to International Stout Day!


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