What is the key ingredient in traditional pesto sauce?

In traditional pesto sauce, the key ingredient is fresh basil. This herb provides the distinctive flavor that defines pesto, setting it apart from other sauces. Basil is typically blended with garlic, pine nuts, parmesan cheese, and olive oil in a process that creates a vibrant green sauce with a rich, aromatic quality. While garlic, olive oil, and pine nuts contribute to the overall flavor and texture of pesto, it is the fresh basil that is fundamental to its identity. The aroma and freshness of the basil are what make pesto a beloved component in various culinary applications, such as pastas, sandwiches, and dressings.