Some spaghetti are cooking in the hot water
Why Your Colander May Be The Reason Your Pasta Is Overcooked
By Elaina Friedman
There are three basic tenets to modern pasta cooking — cooking your pasta in salty water, saving a cup of pasta water for sauce emulsification, and cooking the pasta al dente. If your pasta is still coming out overcooked despite these, you may need to take a second look at your colander.
Kate Shannon of America’s Test Kitchen discovered that many colanders on the market can cause pasta to overcook by not allowing liquid to drain quickly enough, and she recommends colanders with enough ventilation. Food Network’s 2022 roundup of the top five best colanders notes that metal and micro-steel colanders work best for "heavy duty jobs" and hot water, while less expensive plastic ones are better used for cold-rinsing berries, beans, and veggies.
Before you fill up a giant pot with water to cook a couple of servings of pasta, consider using a wide, shallow pan instead, as J. Kenji Lopez-Alt of "Kenji's Cooking Show" does. He uses just enough water to cook the pasta without it sticking to the bottom, noting that less water will make the liquid extra starchy, thus yielding a beautifully emulsified sauce.