As Danny indicates, food is notoriously hard to photograph (or film) in such a way that it looks really tasty. So advertising agencies have always used plenty of trickery in their shots, even before computer graphics were available. So what you see on your screen might not even really exist.
While trying to find the ad though, I came across this from Heinz's Australian marketing team. It's got a certain cute charm to it so, even though it's not actually relevant here, I'll post it anyway: