There's nothing like a test to settle the matter. Fresh grind some coffee. Leave 1/2 it in an open container in your fridge. Put the other half in a ziplock bag and use a straw to remove as much air as you can, then store in a preferably coolish spot away from light. After a week make coffee from each, taking care to use the same amount of coffee and brewing technique for each. Report back your findings. I am being completely serious here. 'Course it's worth mentioning here that for many of us, and that can include myself, a cup of coffee that's 'good enough' is fine and that going to great lengths to avoid flavor loss is not worth the fuss. My dad buys the Costco ground coffee that comes in a big metal can with a sealable plastic lid. He stores it on the kitchen counter next to his coffeemaker for convenience. When the can is first opened the coffee is perfectly drinkable, but by the time he's scraping the bottom of the can -- at least a month later -- the coffee is pretty grim. He doesn't care. And that's the real point.