Baking soda makes spaghetti softer, not firmer.

It makes it softer.

Adding baking soda raises the pH of the water, making it alkaline. That alkalinity breaks down the gluten structure in the pasta faster. Instead of a firm, chewy bite, you get noodles that are more slippery and tender — almost like the texture of ramen or soba.

This is actually a trick used for Asian noodles, where you want that springy, yellow noodle texture. But for Italian spaghetti? You’re working against yourself. The firmer you want the pasta, the more you want the water to be neutral or even slightly acidic (a drop of lemon juice or vinegar can tighten the noodles a bit).

Alkaline water is great if you want spaghetti that falls apart. Not great if you want al dente.

Save the baking soda for your ramen.