To prevent pasta from sticking, use plenty of water, stir frequently, and add salt to the water before adding the pasta. A small amount of oil can also help, but is generally not necessary.
Preventing pasta from sticking together involves a few key steps during the boiling process:
Use a Large Pot with Plenty of Water: The more water you use, the more diluted the starches released by the pasta will be. A good rule of thumb is to use at least 6 quarts of water for every pound of pasta.
Add Salt to the Water: Salting the water not only seasons the pasta but also helps to prevent it from sticking. Add the salt after the water comes to a boil.
Add Pasta to Rapidly Boiling Water: Make sure the water is at a rolling boil before adding the pasta. Adding pasta to lukewarm water will cause it to become sticky.
Stir Frequently: Stir the pasta immediately after adding it to the boiling water and then continue to stir it frequently, especially during the first few minutes of cooking. This helps to separate the strands and prevent them from clumping together.
Cook Al Dente: Overcooked pasta is more likely to stick together. Cook the pasta until it is al dente, meaning 'to the tooth,' or slightly firm.
Avoid rinsing pasta after cooking unless you are making a cold pasta salad. Rinsing removes the starch that helps the sauce adhere to the pasta. For most hot pasta dishes, the starchy water clinging to the pasta is desirable.