For all that some brewers boast of their heritage, few of the beers on sale today are genuinely old. And for good reason: breweries are businesses which need to innovate to survive, adopting new techniques and equipment, adapting to the changing availability of ingredients and responding to shifts in customer taste – tendency turbo-charged by the craft beer revolution. So it’s becoming increasingly hard to find a beer made in the same way as it was even a decade ago, let alone several.

Few producers have the confidence, reputation and market position to dare manage their core brands on the ‘if it ain’t broke, don’t fix it’ policy. One that thankfully does is the legendary English independent family brewer, Harvey’s, founded in 1790 in Lewes, East Sussex. Its best seller, Sussex Best Bitter, has changed little since launching in 1955. The beer is emblematic of a brewery that’s evolved in a measured way while recognising that its tradition is its strength: as the unofficial Sussex motto that’s now part of its branding states, “we wunt be druv” (we won’t be driven).

Well-hopped pale ales weren’t new – Harvey’s was already brewing an IPA ultimately derived from the 18^th century export style – but before the war, the market was dominated by often darker mild ales, which still accounted for 75% of its output in 1945. Bitters and pale ales were hoppier and therefore more expensive, the preserve of the boss drinking in the saloon or lounge of the local pub, rather than the worker in the public bar on the other side of the building.

For various reasons, both the average strength of British beers and the range of styles declined over the first half of the 20^th century, but brewers retained the technique of cask conditioning while their colleagues abroad were switching to pressurised kegs. Easy drinking, well-balanced, subtly flavoured ales, relatively low in alcohol, worked well with the slightly lower carbonation and warmer serving temperatures achievable on cask. Strengths had plunged in the straitened circumstances of wartime, with milds sinking to 2.5% or below, but with rationing easing by the 1950s, customers appreciated something a bit stronger and sweeter. And bitter, with its more upmarket image to suit the aspirational and egalitarian atmosphere of a growing economy, hit the spot.

As Harvey’s head brewer and joint managing director Miles Jenner points out, combine this with the southeast English preference for a good bite of hops and it’s easy to see how the beer, known simply as Best Bitter until 1970, evolved as it did. Accounting for a good 85% of sales, most of those in cask, it’s an indisputable Flagship, though the Victorian tower brewery with its twin mash tuns (one made in 1926 though bought second hand in 1954, the other from 1985) and open fermenters produces a wide range of other great beers, including a fine mild and a textbook classic imperial stout. Remarkably, the yeast, obtained from John Smith of Tadcaster in 1957, has been repitched from brew to brew ever since without being recultivated, lending a house character so badly missed in the output of those contemporary brewers who go on an internet shopping expedition with every gyle.

One of the industry’s great characters and greatest experts, Miles has beer in his blood. His family owned the now-defunct Jenner’s brewery in Southwark, London, between 1787 and 1938 and his father, A. A. Jenner, was head brewer at Harvey’s from 1946 to 1984. Miles himself has been with the company for 40 years, 34 of them as head brewer. Besides brewing world class beer, he’s an actor and performer, known for a one man show, Alphonso, about music hall artist Billy Merson, and is currently helping create a theatre at the brewery.

It might seem most appropriate to taste Harvey’s beside the Ouse in Lewes, perhaps at the John Harvey Tavern opposite the brewhouse. But it happens the company owns one of the best pubs in London, the Royal Oak in the Borough, just a hop from the site of the old Jenner’s brewery. It’s a Victorian corner pub beside the original alignment of Roman Watling Street – the road from London to the Kent coast taken by Geoffrey Chaucer’s pilgrims and later the main artery of the hop trade. It happily preserves a two-bar layout, although no longer divided between workers and bosses, with neat and clean but unpretentious wooden furniture and corners of the sort that encourage lingering for a second or third pint.

Heritage bar fittings include a wood and engraved glass screen with a hatch that once served a ‘jug and bottle’ with a separate door for takeaways. Among the pictures and memorabilia on the walls is a pre-war Harvey’s price list offering mild at 20/- (£1) a firkin and IPA at 30/-. Like the brewery, the pub respects tradition in a way that doesn’t preclude unobtrusively moving with the times and remains welcoming to the diverse and changing communities that surround it.

Once the only Harvey’s pub in London (there are now two others), under a longstanding former leaseholder it built up a formidable reputation for the quality of its house ales on cask, alongside the widest bottled range outside Lewes. The current youthful manager, James Woollard, a Sussex man who grew up drinking the brewery’s products, has set himself the challenge of keeping the best cellar in its 45-strong pub estate. It’s a measure of his success that I keep on bumping into brewers from other breweries there, and not just from the UK.

The pint I order to take tasting notes for this piece is flawlessly kept, at a pleasantly cool temperature, with a firm and vibrant but soft carbonation and a dense, foamy head. The colour is a classic amber brown, with a copper-like shine. The aroma is mainly malty, with a waft of fine orange peel, grassy resins, apricot jam and honey. Given its low alcohol content, the palate is impressively full and dense, again mainly biscuity and malty with notes of autumn fruit, nuts and light yeasty esters, with that loose carbonation tantalising the tongue. Dryness in the mouth balances a sweetish background, and after a brief burst of juicy malt on the swallow, firm, earthy, peppery hops grip the finish: this is indubitably a bitter beer, though with a politeness that leaves room for more delicate notes of honey and orange.

‘Balance’ is a watchword in any good brewery and the Harvey’s experience demonstrates the principle in action: bitter and sweet, drinkability and complexity, innovation and tradition, all in one irresistible package.