It was a calm and balmy morning in September 2018 when winemaker Antonio Arrighi first plunged a basket of grapes into the Mediterranean Sea. His neighbours on the sun-drenched Italian island of Elba watched in disbelief. “Has Antonio gone crazy?”

Indeed, as the bunches sank beneath the water, where they would stay for five days, Arrighi felt a stroke of mad genius. He was resurrecting the process of creating marine wine—an Ancient Greek delicacy said to be favoured by Julius Caesar.