When they brought back “classic” Coke after the failure of “new” Coke, was that what changed? Because I swear the “classic” just isn’t what it used to be I don’t care what they say.
I've been told the whole thing was a ploy to switch the public from sugar to the high fructose corn syrup (HFC).
Due to rising sugar prices (thanks to lobbying by the American sugar industry to restrict foreign competition), in the late seventies virtually all soda bottlers and candy makers went to fructose as a source for their sweetener. As a result the taste in all the products that transferred from sugar to fructose suffered including Coke. The switch from glass to plastic also hurt. Plastic and fructose. That's why Coke doesn't taste as good as it once did.
Perceptions are funny. In blind taste tests, people strongly preferred the taste of New Coke to "classic" Coke, but people just didn't like what they perceived as messing with an icon.
But other posters are right--switching away from sugar and glass has slightly altered the flavor, but it's probably less noticeable (at all, even?) in blind tests than it is by people who like to complain.