What's the Difference between Porter and Stout?
To understand the difference between porter and stout, you must go back to their childhood in 18th century London. (Photo by Jon Page)

“What’s the difference between a porter and a stout?”

Roasted barley. That’s the usual explanation of what separates porter and stout. Unfortunately that story is total bollocks. The true tale is more complicated, more confusing and much more fun.

Let’s go back to their childhood. Eighteenth-century London with its elegant squares, gin and the birth of industrial-scale brewing. Something that could only have happened in London. Pre-powered transport moving large quantities of beer overland was impractical and expensive. London was the only city in the world with the critical mass of beer drinkers to power an industrial brewing reactor.

The story of porter—the first style to span the world—is one of technology, innovation and taxation. And war.

Brown beer. Sounds uninspiring as a style. But that’s where the roots of porter lie. London beers brewed from 100 percent brown malt. Styles of the time were a simple matrix of base malt, hopping rate and strength. Pale, amber, brown. Beer, ale. Small, common, stout. Porter was a common brown beer. And brown stout was . . . a stout brown beer.

There’s another element in the matrix: age. Mild—young—and stale (sounds dreadful, I know) or keeping – aged. And there’s the innovation of porter. Plenty of punters, or boaters, liked their beer with some age on it. But the brewers weren’t interested. Everything was shipped out at the end of primary fermentation. Aging was left in the hands of landlords or middlemen.

Taking maturation into their own hands transformed the fortunes of London beer brewers. They honed aging of their brown beers, learning empirically that six months in a large vat was enough to get the aged flavor drinkers valued. Then economics took over. Bigger vats, larger-scale brewing, lower costs, bigger profits.

Porter brewers, working on an unprecedentedly large scale, were keen on efficiency. Their mashing schemes—four or five mashes—look crazy today. But they were incredibly efficient in squeezing the last sugars from the grains. In the Age of Enlightenment, science came to their aid, in the form of new instruments.

The thermometer allowed brewers to develop more controlled and efficient mashing methods, while the hydrometer showed what rubbish value brown malt was as a base. Using the hydrometer to measure the gravity of their worts allowed brewers to see exactly how much sugar they extracted from their grains. It was soon obvious that brown malt, despite being cheaper than pale malt was worse value because it only yielded two-thirds of the sugar. All this was happening just as another lot of unpleasantness was kicking off on the continent, and His Majesty’s Government needed money. Lots of it. And where did it find it?

By taxing beer and malt. Creating a massive incentive for cutting your malt bill. With hydrometer in hand, that’s exactly what brewers did, bringing about Porter’s second huge innovation: pale malt as base.

Not that replacing half or more of the brown malt with pale didn’t bring its own problems. How did you get the dark color the man in the pub expected?

The government, always suspicious of brewers using sugar to dodge the malt tax, gave porter brewers a special dispensation to use a sort of caramel coloring around 1800. Then, worried about some taking liberties, banned it again in 1816. (The same act of Parliament also forbade the use of opium in beer.) The next year black malt was invented. Solving the coloring problem.

Porter grists went from 100 percent brown malt in 1760 to 40 percent in 1800 and usually below 20 percent after 1820.

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Black malt made porter darker than ever and changed its flavor. Older drinkers were bound to grumble.

Porter and stout recipes continued to evolve in the 19th and 20th century. After 1880, when the use of unmalted grains was permitted, a new coloring material arrived: roasted barley. (Before this date brewers were liable to a heavy fine for having any unmalted grain – with the exception of oats to feed their horses – on their premises.) London brewers weren’t all enthusiastic. Some used it and some didn’t. Those that did used it in all their black beers,  porter and stout. For a very good reason.

Whitbread Brewing records from 1905.
Whitbread Brewing records from 1905. (Photo by Ron Pattinson)

World War I (1914 to 1918) knocked the stuffing out of British beer, but porter in particular. It went from a reasonable 5% ABV to a watery 3%. The end was in sight. Many drinkers switched to stout, which itself had fallen in strength to around the level of pre-war porter. While porter became the tipple of the old blokes huddled in a corner. No style ever recovers from that. No one under 30 wants to drink what granddad’s having. Porter limped along in London until the next war, when its light finally went out.

Returning to the efficiency theme, there’s another technique that’s brilliant at getting every last drop of goodness from the malt. Parti-gyling. Popular with London brewers from the mists of time until . . . today.

Parti-gyling isn’t what you think it is. Almost all modern descriptions get it badly wrong. It isn’t—after 1800 at least—using the first runnings to make one beer and the second and third for others.  It’s much more sophisticated than that.

Porter brewers mashed several times. The worts from each mash were hopped and boiled separately, then blended to produce whatever beers were required. Two, three or even four beers were assembled from blends of each of the worts.

It’s a very efficient way of making not just huge volumes of a beer, but also relatively small amounts of stronger beers. Or any amount of any strength beer. With their brew lengths of hundreds of barrels, London’s porter brewers couldn’t brew the strongest Stouts single-gyle. The amount they could sell would barely have covered the false bottoms of their massive mash tuns.

That’s why they often parti-gyled their stouts with porter. You can probably see where this is going. The recipes for porter and stout were, by definition, identical, as they were brewed together.

Porter disappeared completely from the British Isles in the early 1970s when Guinness discontinued their version. But only for a few years. A couple re-appeared in the late 1970s and since then the style has made a small comeback, with beers like Fullers London Porter leading the way.

The difference between porter and stout? All stouts are types of porter. But not all porters are stouts. Only the stronger ones.

Ron Pattinson is a British beer writer and historian who lives in Amsterdam. He has spent the last 15 years researching and obsessing over many beer-related topics. His European Beer Guide has pointed countless beer lovers in the direction of good beer across Europe. While over on his Shut up About Barclay Perkins blog, he writes about beer history, mostly the history of British beer styles, but with excursions into German Austrian, Dutch and Scandinavian beer history. He is the author of many books about beer history, mostly significant for their single-word titles, such as “Porter!“, “Mild!” and “Bitter!“.  Each month he writes for BeerAdvocate magazine about beer history. He recently published a book on brewing historic beers called “The Home Brewer’s Gude to Vintage Beer“. He is married and the father of two teenage sons.