A common method used is to add a whole potato. Supposedly it will soak up much of the salt, cutting the amount of salt once you simply discard the cooked potato. It’s a nice idea in theory, but the truth is you’re unlikely to notice much difference.
However, the reasoning behind it is far from absurd. A potato will add more bulk and more starch to the pot. But you can get the same effect by adding, say, a thick slice of bread. Let’s look at some more reliable ways to fix too much salt using extra bulk or starch.
Firstly, by bulking up your dish you are effectively diluting it, lowering the concentration of salt. If possible, you can simply add more of the same ingredients, but this might not be an option if you think they won’t cook fully at this stage of preparation. Frankly, the most failsafe method is simply to cook another batch of the food, this time without salt, and then mix it in with the batch that’s too salty.
Adding starchy ingredients follows a similar principle as it will effectively bulk up your dish too. But stirring in some cooked (and unsalted, obviously) rice, barley, or other grains, and even pasta or couscous, will absorb quite a bit of the salt. You’ll also need to add a bit more liquid too, but things should soon balance out. If you want to know how to make gravy less salty, or even a sauce or soup, this is an excellent method. Depending on just how salty the food was to begin with, it’s up to you whether to sieve out the starchy ingredients once they’ve done their job, or simply blend them right in with a soup gun.