General Cooking Questions

Pasta foam... the foam that you get when you put pasta (any dried pasta) into hot water.

I’ve noticed that if the pot is uncovered (at least for the few minutes before boiling), I get no foam. But when I put the pasta in a tad early (or if I cover the water during the heating), I get lots of foam.

I’ve learned to put the pasta in to boiling water, but what about the science behind it? What is causing the water to foam?