Walk into any grocery store and you'll see bags of coffee stamped with a 'best by' date. It's a nice gesture, but here's the thing: that date is mostly guesswork. It's set by the manufacturer, often based on how long they think the coffee will stay "acceptable"—not when it tastes best. For specialty coffee, the number you should be hunting for is the roast date. It's the only honest clock on the bag.