Pasta recipes almost always call for cooking noodles al dente, meaning they are tender but still have a somewhat firm texture (“al dente” is Italian for “to the tooth”). But what exactly happens to dried pasta as it reaches the al dente stage?
Dried pasta is a complex of starch granules held together by protein.
When pasta is boiled, the starch granules on the surface of the pasta absorb water and swell, and some eventually burst, releasing starch into the cooking water. The granules just beneath the pasta’s surface don’t become as hydrated and merely swell without bursting.
Finally, the starch at the very center of the pasta becomes only partially hydrated, so the center retains a slightly firm bite and a faint white core that means it’s been cooked al dente.