Though many people assume cask beer “has existed from the time brewing was first instituted in this country”, as a 1923 manual for licensees puts it, real ale as we know and enjoy it today is, like so many aspects of modern brewing, largely a product of late 19th-century innovation.

Once beer was brewed mainly for local consumption by a multiplicity of small producers, not only dedicated brewing businesses but brewhouses in pubs, institutions and large country houses. Much was drunk as soon as it had finished fermenting, but as the use of hops spread in the 16th and 17th centuries, brewers exploited the herb’s antiseptic and stabilising properties, together with high alcohol levels, to create beers that would keep for several years or more. This helped provide drinkable beer even in warmer weather when controlling fermentation was near-impossible.

The large-scale industrial brewers of the 18th century built their businesses on variants of these strong, long-matured beers, sometimes keeping porters and pale ales in wooden barrels and tuns for two or more years. Such beer inevitably underwent a lengthy and complex secondary fermentation with wild yeasts and acidic bacteria, attaining a flavour profile akin to Belgian sour brown ales or craft-brewed farmhouse, barrel-aged and “Bretted” beers.

Tastes in the 19th century shifted towards lighter, fresher “mild” products. License deregulation in 1830 facilitated a profusion of home-brewing beer houses which lacked the resources for long ageing and therefore concentrated on fresher styles. Technological improvements, particularly the microbiological discoveries of Louis Pasteur and others from the 1860s onwards, made brewing such beers easier. They could now be shipped longer distances in a shorter time thanks to improved transport, and as they didn’t have to keep for long, both strengths and hop rates could be reduced.

Mild was originally an adjective that could be applied to a variety of styles, but by the 1870s it meant a brewery’s basic draught ale, designed to be drunk young with a minimum of hops and relatively low in alcohol. It was soon joined at the bar by cask versions of pale ale, made with similar methods but with a little more hops and therefore dubbed bitter by drinkers, prompting brewers to underline the contrast by darkening their milds. Cask versions of older styles were also brewed, including porters, stouts and dark amber Burton ales. At a time when breweries in other countries were adopting lager brewed to Bavarian models, British brewers considered they didn’t need to, as they already had a light, refreshing, easy-drinking beer suited to the modern industrial world.

Early 20th-century technical brewing writers noted the near-complete shift from matured, stale beers to fresh, mild ones, distinguishing the true secondary fermentation in the former from a modern cask beer, where the activity is just a continuation of the initial fermentation, with the same yeast strain, just enough to provide carbonation and some additional complexity. Most brewers expected the market would eventually shift to more highly carbonated bottled beers, but things didn’t turn out as expected.

Two world wars brought ingredients and labour shortages, taxation, physical destruction, and an increased burden of regulation. The parlous state of brewing following the second war triggered a wave of consolidation, the merger mania of the 1950s and 1960s, from which seven huge combines emerged to dominate the market. Their attempts to replace cask with pasteurised, force-carbonated keg beers were resisted by consumers, leading to the foundation of CAMRA in 1971 and the resurgence of the cask format.

The beer culture campaigners sought to preserve was already reduced from its turn-of-the-century peak. The 5.5 per cent ABV of a pre-World War I mild ale had contracted to 3 per cent or less, and British beer was now on average around one per cent below international standards. Luckily, with its lower carbonation and slightly warmer serving temperature, cask dispense flattered lighter, subtler beers. Early editions of the Good Beer Guide needed only three symbols to encapsulate the repertoire of most breweries: one for mild, another for bitter, and an occasional third for old ale or special. Thankfully, times have changed once again, and the variety and quality of both cask and other beer on offer to drinkers in the 2020s is likely the best it’s ever been.

Des de Moor’s latest book Cask Beer: the real story of Britain’s unique beer culture, a detailed but accessible guide to the past, present and future of cask, will be published by CAMRA Books in late summer 2023.