Cooking Pasta the Right Way
from Micol Negrin, http://www.rusticocooking.com/grilling.htm

Micol Negrin, author of several Italian cookbooks, says below that you should never rinse pasta after cooking it. She is assuming here that you are adding a sauce to your pasta. If you are making a cold pasta salad, it is best to rinse the pasta with cold water to stop the cooking. Be sure to drain well.

"Cooking pasta the right way... We could do a whole class just on this subject. After all, if your pasta isn't properly cooked, no sauce can mask its shortcomings. So here are ten things to keep in mind when cooking pasta...

  1. First of all, start with a big pot. None of those squat pans, and no need for nonstick unless you happen to have only a nonstick stockpot.
  2. Bring 4 cups of water to a boil for every 3 and 1/2 ounces of pasta you intend to cook. The water should be at a rolling boil when you add the pasta.
  3. Add about 1 tablespoon of salt per quart of water when the water comes to a boil (if you add it earlier, it will simply make the water come to a boil more slowly).
  4. Don't add oil! The pasta won't stick together unless you don't stir it often enough as it cooks. (Adding oil to the water will create a slippery surface on the pasta; the sauce will adhere poorly to the pasta when it's time to combine the two.)
  5. Add the pasta all at once, and stir with a long-handled tool. If you are making long pasta, keep stirring until it becomes supple, loses rigidity, and is entirely submerged in the water.
  6. Keep the water boiling the whole time as the pasta cooks: to do this, cover the pot with a lid. (If the pasta water is not boiling, the outside of the pasta will be overcooked by the time the inside is al dente.)
  7. Stir the pasta every minute or so. This is crucial to prevent sticking and to ensure even cooking.
  8. Check often to see how the pasta is coming along, and drain it when it's [not quite] al dente (meaning to the tooth, because it should offer a little bite when it's drained): there should still be a thin white dot at the center. (Pasta drained when it is al dente has been shown to be more easily digested by the human organism... So it's not just a matter of taste!)
  9. Reserve about 1 cup of the cooking water before you drain the pasta. Use as much of this reserved pasta cooking water as needed to thin out your sauce (this allows you to cut down on olive oil or butter). Also, because the pasta cooking water is so rich in starch, it helps the sauce bind to the pasta--making for pasta with a lovely, velvety quality. And, the residual heat in the reserved pasta cooking water will help your pasta stay hot for longer...
  10. NEVER rinse pasta after you drain it, even if you plan to serve the pasta cold [for salads I rinse with cold water to stop the cooking}: it will wash out the starch and much of the flavor. (To cool drained pasta for use in cold dishes, toss it with a touch of olive oil and spread it out on a large tray until it reaches room temperature--about 15 minutes.)

Your pasta is now ready to toss with sauce in a heated bowl or large skillet... Buon appetito!

One of the cardinal rules of pasta cookery is to NEVER rinse cooked pasta once you've drained it. Why? Because rinsing pasta would strip it of some of its lovely starchy outer coat, which in turn would make it slippery rather than velvety and would lessen its ability to cling to sauce. The starch on the pasta is essential for the proper binding of sauce to pasta."

‘Mantecare’ – How Italians combine pasta with sauce
from http://www.independent.co.uk/

The act of skillfully combining cooked pasta with a sauce is something Italians call the ‘mantecare’ or ‘mantecatura’. This literally means to emulsify the starch from the pasta with the oil or butter in the sauce to make that creamy loose pasta finish that is so compelling. It is not an easy thing to do, but once understood and cracked you will never look back.

“Drain the pasta but keep a cup of the cooking water. Tip the hot drained pasta into the pan containing the sauce, adding a splash of the cooking water (about 60 ml) and toss with gusto over a high heat until the pasta looks creamy and well coated.”

This is key for recipes like spaghetti vongole, [Linguine Con Vongole - Linguine With Clam Sauce] where the olive oil and starchy water mixed with the garlic, clam juice and white wine create that compelling and super-tasty slippery sauce.

There are two ways Italians combine pasta with sauce:

Hot pasta into hot sauce: Scratch cook a quick sauce in a sauté pan and tip in the hot drained pasta. Add a splash of cooking water, toss with gusto and serve.

Hot pasta into cold sauce: Place the ingredients in a serving bowl, using raw crushed garlic, olive oil and ingredients of choice, and tip the hot drained pasta directly into the bowl to unlock the flavours and aromatics. Toss with gusto and serve.