Salt can be a tricky ingredient to work with. If you use too little your food may taste bland and unfocused, while too much salt quickly leaves a dish inedible or at least unpleasant to the palate. Unlike most other flavorings, salt won't fade with extended cooking. If anything, it becomes more prominent, as other flavors fade. You can't extract salt from a cooked dish if you've used too much, but there are a number of proven ways to reduce its impact.
"Too much" salt is never a hard and fast quantity. It's just a question of whether you've used more than you should, given the amount of food you're preparing. That means the simplest way to fix things is to increase the rest of your recipe. As the batch gets bigger, the amount of salt becomes proportionally smaller, until the flavors eventually balance again.
- If you're making soup, add unsalted broth until the salt is back to a suitable level.
- If you're making pasta sauce, add more tomatoes or cream.
- If you're preparing a batch of stew or a casserole -- anything that can be refrigerated or frozen for later -- the same principle applies. Increase the level of unsalted liquids.
It's not always practical to increase the size of your batch, unfortunately. You might not have the ingredients or enough time to still get dinner on the table. In those cases, you can still apply the same principle by removing some of the over-salted food. Dip out some of the broth, or sauce as the case may be, and replace it with an equal quantity of broth, water, cream, cooked beans or whatever ingredient is appropriate to the dish. It's a less drastic and more practical version of the same fix.
Dilution is the only way to really reduce the amount of salt in a dish, but you can mask its impact by distracting your taste buds with competing flavors. Adding sweetness, tart acidity or chili heat -- whichever is appropriate for the dish you're making -- can sometimes save the day. It won't reduce the actual sodium level in the food, but at least makes it more palatable.
One widely circulated piece of advice is to cut up a raw potato and add it to your dish, where it supposedly absorbs excess salt from your meal. Unfortunately, no matter how many of your friends swear by this tip, it simply doesn't work. A number of science-minded food writers have tested and debunked the technique.
For example, former chemistry professor Robert Wolke addressed it capably in his book "What Einstein Told his Cook." While the potato definitely tastes salty afterwards, it absorbs water as well as salt and leaves their relative proportions unchanged.