“One Guinness, please!” says a customer to a barkeep, who flips a branded pint glass and catches it under the tap. The barkeep begins a multistep pour process lasting precisely 119.5 seconds, which, whether it’s a marketing gimmick or a marvel of alcoholic engineering, has become a beloved ritual in Irish pubs worldwide. The result: a rich stout with a perfect froth layer like an earthy milkshake.The Guinness brewery has been known for innovative methods ever since founder Arthur Guinness signed...