The aspartame will have lost it's sweetness. The HFCS (corn syrup) is still ok. So it will taste like a slightly watered down half sweetened coke classic.
Now if you mix it with Coke Zero or Classic coke at a high enough ratio you might be able to make a mix that isn't noticeably less sweet.
If you buy a liquid sweetener and add it to the stale C2 you could also "fix" the drink but that is something I've never tried. Powdered sweeteners are out of the question as they cause the drink to fizz out of control.
It's one of the reasons why diet drinks of lesser bought brands are so hard to find on the market. The company can't afford to take the hit of a slow selling diet drink. If it doesn't sell quick it's worthless.
As an example my mom gave me some expired coke zero bottles and they had no sweetness left at all. I poured them all out as soon as I tasted the first sip.
Last edited by Mana211; 04-21-2007 at 08:19 PM.
I have 12 packs in my fridge, closet, trunk, and occasionally in random locations.