While failing to emulate Massimo Bottura’s pasta recipes or just trying to make a quick-fix-dinner of packaged mac-n-cheese, I’ve often found myself asking the same (enter expletive here) line of questioning about water, salt, and the boiling point:
If I heavily salt a pot of water before placing it over a lit stove, how does it affect the time it takes to boil?
Will it take shorter or longer to boil?
Now I can’t remember, should I wait for it to boil first?
Will adding salt raise or lower water’s boiling point?
And, what does the boiling point even mean?
What in the world does salt do to water, anyway?
Should I have ordered take out instead?
Water molecules are like miniature, mickey-mouse-shaped magnets. With positive and negative sides, these microscopic water molecules can attract, fall into line, and intertwine. This invisible force of attraction creates a bobbing, wriggling sea of connected water molecules. The V-shaped aqueous bits are constantly in a tug-of-war with encapsulating air molecules.
Water molecules can be pulled away from each other when enough heat is injected to increase the liquid’s temperature—the boiling point. The teeny cartoon-rodent-head-shapes bounce and mix with the lighter, hovering atoms of air forming gas as the liquid begins to steam and bubble. If you trap the water and air molecules in the pot with a lid, this bouncing and mixing happen even faster, bringing the water to a roaring boil.
When you add salt to water, the briny crystals break up into charged particles that attract matching water molecule surfaces and, like magnetic super-glue, makes them stickier. This saline solution, sturdier than water molecules alone, requires additional heat to free up water molecules entangled with charged particles—the saltier the sea, the more energy is required for it to boil.
Oppositely, adding salt to liquid water lowers the freezing point—the temperature that freezes water molecules into an icy grid. Salty water must get colder than pure water to freeze, which is why sidewalks get salted after snowfall—to melt icy streets into slush.
So, when you’re pressed to make some pasta, put on the lid, turn on the heat, and wait to salt the water until after it boils.