The business, which owns 182 managed and tenanted pubs across the West Country, also supplies more than 3,000 free trade customers in the region.
Production recently began with 440 barrels of the brewer's flagship ale Tribute, accounting for almost half of St Austell’s weekly barrelage.
It is currently producing more than 1,000 brewer’s barrels a week (the equivalent of 294,000 pints), which will be scaled up gradually in the weeks and months ahead.
St Austell is also preparing to brew other beers including Proper Job, Cornish Best, Trelawny and Hicks.
Prophecy and Draught Gem are also in production at Bath Ales’ Hare Brewery, which St Austell acquired in 2016.
It is producing keg brands for both breweries including Proper Job, Mena Dhu, Montery and Dark Side.
The brewery said throughout the lockdown period, entire production efforts have been centred on bottling and canning core beer brands for the off-trade, resulting in an uptick in sales of a third (32%).
Since the enforced pub closures in March, St Austell Brewery and Bath Ales have also seen online shop services soar of more than 1000% combined, compared to 2019.
St Austell beer and brands managing director Andrew Turner said: “I’m pleased to say we are back in production and getting ready for the long-awaited reopening of our pubs, which we are hoping the Government will confirm as soon as possible.
“We are proud to be playing our part in the national effort to restock cellars with fresh beer. Cask beer is an integral part of pub culture in the UK, there’s nothing quite like it."
He added: “It has been months since we have brewed draught beer – the longest time since 1851 – so we are delighted to see product up and running again.”
St Austell isn't alone in beginning to brew for pubs again as other breweries across the nation have restarted operations to produce cask ale.
Black Sheep Brewery has restarted production of cask beer in Masham, North Yorkshire after three months out of action, with 100 barrels of its Black Sheep Best Bitter.
Yorkshire-based brewery Timothy Taylor announced it had started to produce cask again for the first time since the lockdown was enforced in March.
Robinsons Brewery also announced that it had started brewing with pubs reopening in mind. The Stockport-based operation said it has plans to deliver cask and keg beers in advance of the 4 July date.