The Cornish brewery that makes Doom Bar ale is to be closed by its US owner, throwing the popular beer brand’s future into doubt and putting about 200 jobs at risk.

The drinks company Molson Coors said it plans to shut Sharp’s Brewery in Rock, along with its national call centre in Wales, saying it was “no longer financially sustainable”.

The Chicago-based company, which bought Sharp’s 15 years ago, said it was planning to close the site by the end of this year but it “remains committed” to Sharp’s beer brands.

Sharp was founded in 1994, and most its sales come from Doom Bar, which is among the bestselling cask ales in the UK, and was named after a notoriously dangerous sandbank in Cornwall’s Camel estuary. Sharp’s also makes Atlantic and Twin Coast pale ales.

Tom Stainer, chief executive of the Campaign for Real Ale (Camra) said it was “just another example of a global brewing giant destroying the nation’s cask brewing heritage. Sharp’s has been brewing cask for over 30 years and this will just be dismantled overnight.”

Molson Coors said it was exploring potential deals with other producers to keep making the beer, including brewing in other parts of the country. But Stainer added that any plans to produce the Cornish beers outside the region “would be a disgrace”.

“We are losing far too many cask brands and the breweries who craft them at the hands of global brewers more interested in profit than our brewing heritage, and making sure drinkers can enjoy authentic products,” he said.

When Molson Coors bought the Cornwall site for £20m in 2011, it said it was “100% committed to real ale and cask beer at Rock” and even suggested the brewery could be expanded.

But on Thursday, the US firm, which also makes Carling, Coors Light and Staropramen, said it had explored “every alternative option to make the site financially sustainable”.

The plan was part of a broader restructuring to “unlock efficiencies and cost-savings to fuel the company’s long-term growth”, it added.

Ben Maguire, the Liberal Democrat MP for North Cornwall, said the closure was “a hammer blow for the local economy, and for the hospitality sector here in Cornwall that is already on its last legs”.

He said: “It is deeply disappointing to see an American multinational move production out of Cornwall, and ministers should look at giving Cornish beers, ales, and other drinks the same protections as the Cornish pasty, so that what is branded Cornish is genuinely made here.”

Simon Kerry, managing director of Molson Coors in the UK and Ireland, said the closure “has not been an easy decision for us to make … However, the site is no longer financially sustainable as part of our national production network.”

About 50 people face redundancy at the Rock brewery, as well as the 150 who work at its call centre in Wales. Molson Coors said it was closing that site because nearly 90% of its customer orders were now made online.

Molson Coors had “evolved our business as part of our digitisation journey,” Kerry said, adding: “The proposed closure of our National Contact Centre is no reflection on the brilliant work of our teams, but is in response to these changes.”