You're cooking your favorite dish, and the phone rings. You get involved in chatting with your friend, and suddenly remember you haven't put the salt in. You think, well, it's just about done but I'll add the salt now, anyway. You put in the salt shortly before you take the dish off the stove to serve it. As you're eating you think it tastes a lot saltier than usual. Does it really, or is it just your imagination?
The question is, if you want something to taste salty, when is the best time to salt it: before you cook it, during cooking, at the end of cooking, or just before you eat it?
To get to the answer let's consider the most basic thing about tasting. Before you can taste anything it must reach your tongue. That's obvious enough, but it has a lot to do with the seasoning of food. Generally speaking the more savory particles that reach the taste buds, the stronger the taste. Salt buried in a lump of food will likely be swallowed untasted, and that's where a lot of it ends up if you salt the food early in the cooking process.
Salt added later in cooking tends to remain on the surface of the food so more of it reaches your taste buds, and thus the food tastes saltier. Think of potato chips with their salty surfaces. One ounce of chips has about the same amount of salt as a slice of wheat bread. Which tastes saltier?
The answer to the question of when to salt to get the saltiest taste is: the later the better.
A consequence of this is that since you get a saltier taste by adding it later, you can use less salt. This can be helpful to those trying to cut back on salt; put it in later and you don't need as much.