What's the trick for telling whether...

We usually just scoop out a bit and take a bite, but if you’d like a more scientific method, try this: Cut a piece of the pasta in half. If it is undercooked, a white dot or line will be clearly visible in the center. This is the portion that has not adequately absorbed the water yet. If you want your pasta al dente, you should see just a speck of white when you cut it.