What does it mean when mountain dew changes colors and taste funny?

Mountain dew changing colors and tasting funny is likely caused by oxidation, which is a chemical reaction between oxygen and the ingredients in the drink. Over time, oxygen can break down the flavor molecules, causing the taste of the drink to become flat and off-putting. Additionally, the preservatives and colorings used in the drink may also react with oxygen, leading to a change in color. It's recommended to consume Mountain Dew and other carbonated drinks before the best-before date to enjoy the optimal flavor and quality.