Taste is our most indulgent sense but it is only in recent years that we have started to understand why we really love the foods we do - and it is a lot more surprising than you might think. There may a way to make food taste sweeter without adding any extra sugar and it is all down to a trick that happens in your brain. Horizon meets the scientist who has grown the perfect tomato, that is sweeter and juicier than anything you are likely to find on a shelf, as well as the men and women hoping to become elite, professional tasters.