Some articles say it's reaction with the plastic. But others, and an interview I heard once with someone from Coca-Cola, say it's because plastic bottles are mo

Some articles say it's reaction with the plastic. But others, and an interview I heard once with someone from Coca-Cola, say it's because plastic bottles are more permeable to CO₂ gas than glass bottles or metal cans. That is, they leak fizz faster. So more CO₂ is added to the plastic bottle version of the drink to ensure it stays fizzy over its shelf life. This excess CO₂ (which is carbonic acid H₂CO₃ when dissolved in water) changes the taste slightly.