The stout revival continues unabated. The shock news that Guinness is now the biggest-selling beer in Britain has prompted many other breweries to produce their versions of the black stuff.

Now Shepherd Neame, the country’s oldest brewer, has jumped on the bandwagon. Its draught Whitstable Bay Black Stout (4.2 per cent) is now available in selected Waitrose stores – including St Albans -- at £2.25 a bottle.

Shepherd Neame was founded in 1698 in Faversham in the heart of the Kent hop fields. It’s famous for such ales as Spitfire and Bishops Finger and it has added to its range with a series of beers labelled Whitstable Bay. The beers include pale and red ales and some organic products.

The Neame family is still in firm control of a business that pumps out 200,000 barrels a year. The family takes great pride in using Kentish materials in its beers and it has invested in the National Hop Collection near Faversham where some 70 different English hop varieties are grown.

It has had a long association with dark beers, brewing both porter and stout since the 18th century. One of its dark beers has a fascinating back story.

In 2012 the brewery’s archivist, John Owen, found an old leather-bound recipe book, covered in dust and cobwebs, in a dark corner of the brewery’s cellars.

The recipes were from the 19th century but John couldn’t read them as they were written in code.

He discovered that at the time there was another large brewery called Rigdens across the road and the Neames were worried that a disgruntled employee might take their recipes and hand them to Rigdens in exchange for money.

As a result the family instructed their brewers to keep their recipes secret by writing them in code.

John Owen sat down with a member of the brewing team, Stewart Main, and they attacked the recipes with all the zeal of the code breakers at Bletchley Park during World War Two.

Their work took several months as they painstakingly unravelled the ingredients for two beers brewed in the 1860s, Double Stout (5.2 per cent) and India Pale Ale (6.1 per cent).

The recipes were divided into columns and included such groups of letters as GBX, JBX and SBX, written in faded copper-plate writing. Stewart Main’s experience told him the letters referred to the malts and hops used in each beer along with the amounts.

John and Stewart tried all possible permutations of the letters until they were satisfied they had managed to unravel the recipes. Stewart then brewed them in a special pilot plant used to try out new recipes.

The beers are now sold commercially. Double Stout is brewed with pale and roasted malts and is hopped with the finest East Kent Goldings.

Sheperd Neame had the last laugh where secrecy was concerned. Rigdens merged with the large Fremlins Brewery in Maidstone, which was bought in the 20th century by the national brewer Whitbread. The Faversham brewery closed in 1990 and the site is now a supermarket.

Whitstable Bay Black Stout is a superb beer, brewed with four malts, from pale to dark in colour, and hopped with the Kentish Target variety.

It has an aroma of burnt fruits – raisins and sultanas – with notes of dark malt, espresso coffee and spicy hops.

Tart fruit, spicy hops, coffee and roasted grain dominate the palate followed by coffee, bitter chocolate, burnt fruit and hops in the finish.

It’s a joy to drink and you won’t need to break any codes to read the label on the bottle.