I recently tasted some just-opened ketchup vs. a 3/4 empty bottle and the flavor difference was striking. And we go through a lot of ketchup quickly in our household (read "me") so the 3/4 empty bottle couldn't have been open for more than 10 days. Can I attribute this to the tomato oxidizing in the presence of more and more oxygen in the bottle as it empties. Has anyone else noticed this phenomenon?