Asked in ChemistryCooking TechniquesCooking Times and TemperaturesSalt (Sodium Chloride)
Does water boil faster with or without salt?
March 10, 2013 3:14AM
Adding salt to water increases the boiling temperature, causing the water to come to a boil more slowly. This increase in the cooking temperature will, in theory, cause foods boiled in salt water to cook faster. Pure solutions will generally have lower boiling points than mixtures. Adding sugar to the water will have a similar effect but would not be nearly as nice to cook food in!
Note that if pure water is heated up to a high temperature prior to the addition of the salt, the addition could cause the entire pot to start boiling suddenly. This is a result of the grains of salt acting as nucleation sites. This has the effect of making nearly-boiling water actually boil more quickly when salt is added. The tiny amount of salt required to cause a nucleation effect would have no effect on the temperature of the boiling water. In this regard, you can think of the salt as a catalyst, facilitating the change of state of the water from liquid to boiling.
We said "in theory" above because adding salt to water to raise the boiling point for cooking doesn't actually work in practice. The amount of salt you'd typically add to water for cooking would have negligible effect on the boiling temperature. Let's look at some numbers. Assuming fresh water at sea level, you'd need to add 230 grams of table salt to raise the boiling point of one liter of water just 2 degrees C. To raise the boiling point of the two quarts of water you're cooking pasta your pasta in by that same two degrees, you'd have to stir in 435 grams of salt. That's well over half of an entire 737 gram blue Morton salt container! The pasta may cook faster in the hotter water, but people would probably not be coming back for second helpings of your ultra-salty linguini.
Salt added to the cooking water also "hardens" the surface of the starches in pasta, reducing their stickiness. This prevents the pasta from sticking together in clumps. Somewhat counter-intuitively, oil added to boiling water does not reduce the stickiness of the pasta. It does reduce the surface tension of the water, increased by the starches in the pasta. This tends to reduce foaming.
The bottom line is this: You can add a few grains of salt to pure water to kick off the boiling process with nucleation. Beyond that, add salt to water to flavor what you're cooking and to keep the pasta from sticking together. It will not have any measurable effect on cooking temperature or time.