Recently, I stopped adding salt to my water for cooking pasta. I had always been told by my mother that adding salt makes the water boil faster…but everything seemed to be taking the same amount of time.
This seemed like something I hadn’t thought about before but could now easily apply some critical thinking to. But how to go about it?
First, I stared at my pot of water and did some thinking. The general rule that I use is that, when anything with a high boiling point is added to a pure substance with a lower boiling point, the boiling point of the solution will rise. (I’m sure some chemist out there is growling at me.) Table salt has a higher boiling point than water; therefore my salted water should be boiling at a higher temperature than the unsalted water. Does that mean that my pasta would be cooking faster in hotter water? After all, at 125°C, a pressure cooker can get that spaghetti finished in 6 minutes or so, vs. 10 minutes in my pot.
I decided I’d use the lovely engineering reference library I have at work, and found in The Nalco Water Handbook that a 5% NaCl solution will have a boiling point about 0.5°C higher than pure water. Based on the side of my box of salt, ¼ teaspoon = 1.5 g, and I’m just going with my standard estimate for water of 1 mL = 1 g.
This means, that if you have 1 Litre of water, you would have to add 3 Tablespoons of salt to it to see a small change in boiling point. My bag of pasta recommends 1 ½ teaspoons per 1 Litre, enough to change the boiling point by less than 0.1°C. I can get a larger change in boiling point due to elevation alone – just between the bottom and top of one of Edmonton’s downtown high-rises; or between Edmonton and Fort Saskatchewan, cities half an hour apart.
So, that was a rather mundane result, but now I know something that I didn’t before. And really, the important thing to take away from this is that if you don’t like salty pasta, don’t live in fear that you’re making your loved ones wait longer for their dinner.