The Ketchup Conundrum

"Give a baby soup, and then soup with MSG (an amino-acid salt that is pure umami), and the baby will go back for the MSG soup every time, the same way a baby will always prefer water with sugar to water alone. Salt and sugar and umami are primal signals about the food we are eating--about how dense it is in calories, for example, or, in the case of umami, about the presence of proteins and amino acids. What Heinz had done was come up with a condiment that pushed all five of these primal buttons. The taste of Heinz's ketchup began at the tip of the tongue, where our receptors for sweet and salty first appear, moved along the sides, where sour notes seem the strongest, then hit the back of the tongue, for umami and bitter, in one long crescendo. How many things in the supermarket run the sensory spectrum like this?"