An herb-based sauce originating in Italy that is typically made with basil, parsley, pine nuts, garlic, olive oil, and parmesan or romano cheese. Many variations of this sauce exist, which may be different simply by the type of cheese, nuts or herbs, or other ingredients that are used to make the sauce. As an example, a red colored version of pesto, known as "pesto rosso" in Italian, is made with sun-dried tomatoes as one of the key ingredients, in addition to the basil, parsley, garlic, cheese and olive oil. Pesto is traditionally used as a pasta sauce but may be used as a seasoning for other foods as well as an ingredient or topping for appetizers.
Fresh pesto can be kept refrigerated for 2 to 3 days or frozen to be kept for longer periods of time. As the fresh pesto is exposed to air, the outer fringes of the pesto will darken while the inner areas will tend to remain brighter in color. This discoloration of the sauce occurs naturally and is part of the aging process that decreases the full flavor of fresh pesto.