How does the pH of tap water affect the way pasta cooks in a pot?
While pure water has a pH of 7 (neither acidic nor basic), tap water is often alkaline. Water may be naturally alkaline if it contains lots of calcium or magnesium, or your local water authority may be adding alkali to reduce pipe corrosion.
When pasta is immersed in boiling water, its starches begin to absorb water and swell at the same time that the protein network surrounding them grows more elastic. Here’s where pH comes into play: Alkaline water will weaken the protein network, which acts as a sort of protective mesh to contain the starches. This allows starches at the surface of the pasta to absorb water and burst, leaving a sticky residue that causes strands to stick together. Water that’s even slightly acidic, however, can strengthen the protein mesh and prevent starch granules from swelling to the point that they burst.
If you think you have alkaline water, here’s a quick fix: Add 2 teaspoons of lemon juice or white vinegar to 4 quarts of pasta water. This will help prevent your pasta from sticking without affecting its flavor.