As their names suggest, salted and unsalted butter are generally identical other than the salt content. The exact amount of salt that's added to a batch of salted butter varies depending on the manufacturer. Another main difference between the two is that unsalted butter may be fresher. Salt acts as a preservative, so salted butter can last about two weeks longer on a grocery store shelf and in your refrigerator.

Salted butter is most often used in cooking savory dishes. The saltiness adds flavor to sauces or soups. Adding salt yourself can lead to the dishes tasting overly salty, but the small amount of salt in the butter controls the amount of flavor. For instance, adding salted butter to mashed potatoes will make them creamy and will add just the right amount of saltiness. This type of butter is also ideal as a topping. Spread salted butter on bread or melt some over steamed vegetables.

Unsalted butter is used in virtually all baked goods. Recipes for cookies, cakes, and pies will generally call for unsalted butter. The salt content in salted butter will overpower the sweet flavor of these treats. If a recipe for a sweet dish doesn't specify what type of butter you should use, assume that you should use unsalted. Unsalted butter is also ideal for cooking any dish for a person who is trying to limit his salt intake.

It's easy to substitute unsalted butter when making a recipe that calls for salted. Add an extra pinch of salt per tablespoon of unsalted butter, or slowly add salt a pinch at a time and taste the dish until it tastes right. Substituting salted butter for the unsalted variety is not generally a good idea, and should never be done if the recipe doesn't call for salt as well. If the recipe does call for salt, decrease the amount by a quarter teaspoon for every half cup of salted butter you use. Many seasonings such as dry salad dressing mixes also contain salt, and if your recipe directs you to combine dry mix with butter, use unsalted butter.