Should You Add Salt To Boiling Water?

Dec 5, 2011 10:01 am

The Food Scientist answers vexing food questions

photo: <a href="http://www.flickr.com/photos/sriram/">DeathByBokeh</a> on Flickr
photo: DeathByBokeh on Flickr
Salted boiling water = pasta's best friend.
 

There are few ingredients in your kitchen pantry that serve the myriad functions that salt fulfills. In most cases, we use salt — some conservatively, others more liberally — to enhance the flavors of our food. Why that is, exactly — well that’s a question for another day. Perhaps one of the more confounding questions revolves around the use of salt in the kitchen for two specific, yet seemingly opposing tasks. When we make pasta or boil potatoes, we always know to first salt our water.

Why does water boil?

All liquids, including water, have an innate tendency to evaporate when left exposed to the open air, and while the rate of evaporation varies from liquid to liquid, the process of evaporation remains the same. Liquids, like solids and even gases, contain molecules that move at variable speeds through the substance depending on its state; molecules in a solid, such as ice, move much slower than those in a gas, such as steam.

When it comes to boiling water, these molecules collide and transfer energy to one another, sometimes transferring enough to cause water particles to escape from the surface — this is evaporation. As more heat is added to the water, the more intense and faster these collisions become and the more particles will escape as a result. Once the water has reached a certain temperature — in this case 270 212F degrees — there is so much energy held in the liquid that the tendency for particles to evaporate is greater than the tendency to stay in liquid form. At this point, known as the boiling point, the vapor pressure of the water is equal to atmospheric pressure (pressure of the air around us).

So why should you add salt to boiling water?

The strange but scientifically proven phenomenon that occurs when adding salt to water is known as boiling point elevation. By "elevation," I mean that the boiling point is higher than it would be in the absence of salt. This in no way means that your water will boil faster, however, which is a common misconception among cooks. On the contrary, this simply means that salted water will become hotter, and your potatoes or pasta will ultimately cook faster will make your food taste better. You could, in theory, make water boil faster by adding more salt, but it'd probably make for inedible noodles or spuds: you'd need 3 tablespoons of salt in 1 quart of water to increase the boiling point by 1F degree. Remember, no one likes al dente pasta that tastes like a salt lick.

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