Draining pasta before adding it to sauce serves several purposes:
Removing excess water: Pasta is cooked in boiling water, and draining it removes the excess water from the cooking process. This prevents the pasta from becoming soggy and diluting the flavor of the sauce.
Proper sauce consistency: If you add pasta directly from the boiling water to the sauce, some of the starchy pasta water may mix with the sauce, altering its consistency. Draining the pasta helps maintain the desired thickness and texture of the sauce.
Avoid overcooking: Pasta continues to cook after it is removed from boiling water due to residual heat. By draining it promptly, you prevent the pasta from overcooking, ensuring it remains al dente (cooked to be firm but not soft or mushy).
Saucing evenly: When you drain the pasta, it allows you to toss the pasta with the sauce evenly. This ensures that each strand or piece of pasta gets coated with the sauce, enhancing the overall flavor and presentation.
To achieve the best results, it's a common practice to drain the pasta and reserve a small amount of the pasta water. You can then add the drained pasta to the sauce and mix it well, incorporating some of the reserved pasta water if needed to adjust the sauce's consistency and help it adhere better to the pasta.