Bosses at the Three Tuns Brewery, in Bishop's Castle, have been in talks with specialist engineers to make better use of its 370-year-old cellars.
The idea came about after restrictions on the Grade II listed brewery building prevented any expansion upwards or outwards.
The various beers produced at the Three Tuns, off Market Square, are brewed in a vertical Victorian tower where ale topples down a number of chambers into a fermenting tank.
Director of the brewery Bill Bainbridge said the plan would allow a larger tank to be installed underground, meaning ale could be produced in greater quantities.
It comes just 10 years after the brewery was threatened with closure. In 2002 a plan was put forward to turn the brewery, which had closed a number of times, into housing but the premises were bought the following year by John Roberts' Brewing Co Ltd and fully refurbished to secure its future.
A brewing licence was first granted at the site in 1642 and some of the existing brewery dates back to the 17th century. Staff believe it is part of the original brewhouse, which they claim would make the Three Tuns the oldest working brewery in Britain.
Mr Bainbridge said: "We have spent more than £1 million over 10 years and used 200 tonnes of steel to get the brewery to where it is now.
"The investment has led to people from across the world to visit Bishop's Castle.
"We've always pledged to keep the Three Tuns at its current site. We're continuing to think outside the box.
"Our gravitational brewing process cannot be replicated to produce the high qualities of ale and due to our history, relocation is not an option.
"As demand goes through the roof, our expansion is, quite literally, going through the ground.
"We are working with a team of engineers and surveyors and plotting a revolutionary way to excavate into the ground the site sits on."
Depending on planning permission, subterranean work could begin next year, the brewery's 371st year.