Young's, the historic London pub group, has severed its last remaining ties with the brewing industry after 180 years involvement in the making of the cask ale sold in its outlets.

The £15m sale of Young's 40% holding in a Bedfordshire-based brewing joint venture to its partner Charles Wells marks the end of a process that has gradually separated one of London's oldest and most recognisable cask ale brands from the pubs that bear the same name.

The joint venture was set up five years ago after Young's agreed to sell its Ram Brewery site in Wandsworth, south-west London, to property developer Minerva for £69m. The Young's business now consists of 246 mainly freehold pubs, including 26 sites from the acquisition of gastropub group Geronimo Inns in December.

Steve Goodyear, chief executive, insisted that breaking Young's link with its brewing heritage would not have an impact on its pubs, because of a four-year supply agreement. "Young's beer has always been synonymous with the pubs – it is our USP ... We still have, by and large, the same supply agreement as when we entered into the joint venture."

Investors have long argued for splitting brewing and retailing operations – notably activist shareholder Guinness Peat – but was resisted by generations of the founding Young family, who still retain almost 40% of voting stock. Guinness Peat controls about 15%.

The heady mix of beer and shareholder disagreements led to some of the most heated annual shareholder meetings in the early noughties. Despite being in his 80s, former chairman John Young used stunts such as brandishing a megaphone, donning a beekeeping outfit and appearing in boxing gloves to underline his resistance to Guinness Peat ideas. But in 2006 Young's finally bowed to pressure and disposed of the its prime Wandsworth site, which is likely to become a shopping centre incorporating some business units.

John Young died six weeks after contracts were exchanged on the Ram Brewery. Earlier in his career he was lauded for his stubborn refusal in the mid-1960s to stock keg beer in Young's pubs, keeping faith with traditional draught ale processes. The unfashionable move was later seen as an important landmark in the fight to save cask ale.

Responding to the latest move, James Dawson, an analyst at Charles Stanley, said: "The disposal of Young's remaining links to brewing may be considered disappointing by some, but realistically the group had already moved towards greater focus on its retailing operations."

Young's began trading when Charles Young and Anthony Bainbridge bought the Ram Brewery in Wandsworth in 1831, and – until 2006 – the group boasted that the site was the oldest British brewery in continuous operation, with evidence of beer-making going back to the 16th century.

The closure of the Ram prompted rival brewer Fuller, Smith & Turner to brag that it was "the last traditional family-owned brewery remaining in London". Since then it has seen Guinness Peat quietly buying up its shares. Some believe it will seek to pressure the company to sell off its Griffin Brewery in Chiswick.