Watching Water Boil

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.

Tablespoon of saltI 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.

14 Responses to “Watching Water Boil”

  1. Tom says:

    I’m pretty sure the rationale for adding salt to the water was to season the pasta. That’s the reason I heard anyway.

  2. DianaG says:

    You stopped salting the water when cooking pasta. *look of utter disbelief*

    I don’t know what yo say to that.

    You are right to question the addition of salt for reducing boiling time.[1] That’s an old wives tale. But a real reason for adding salt is flavour.[2] Pasta is made from flour and eggs with the TINIEST amount of salt conceivable. In other words, it has no flavour of its own. Salting the water allows you to get flavour IN TO the noodle instead of coating the outside which gives better flavour.[3]

    [1] http://www.seriouseats.com/2010/08/how-to-boil-water-faster-simmer-temperatures.html
    [2] http://youtu.be/i2Fbx_X-09w?t=34s
    [3] http://www.thekitchn.com/thekitchn/tips-techniques/dinner-tip-salt-the-pot-not-the-pasta-144262

  3. Blondin says:

    I remember learning in high school that adding salt made the water boil at a higher temp so that the food cooked faster and I used to pass on this nugget when ever the subject came up. More recently, however, I saw an episode of Alton Brown’s “Good Eats” show where he explained (as you stated) that you would have to add so much salt to make an appreciable difference in boiling temp that the food would be inedible. The only real effect of adding salt to water for boiling vegetables or pasta is to flavour the food.

  4. I remember my junior high science teacher giving us an explanation for this, but can’t remember for the life of me what it was. It had something to do with the conservation of energy in the pot… when the salt dissolves in the water, the NaCl molecules break up in to Sodium and Chlorine ions, and the energy needed to break the ions apart comes from the thermal energy in the water, causing the water/salt mix to boil at a higher temperature… or some such.

    It was over 25 years ago, and I don’t think I really understood it even then, so I could have this completely sideways here. Does this sound familiar (or even plausible) to anyone else? Was my science teacher just spouting nonsense?

  5. Eamon Knight says:

    I thought adding salt was an anti-bumping measure.

    Also: not a chemist here, but I’ll growl at you anyway ;-) . Chemistry means that macroscopic properties are not linearly additive. See eg. “eutectic”, an alloy whose melting point is lower than either of the constituent substances.

  6. DR says:

    1. Don’t ever follow “directions” on packages when cooking pasta.
    2. DO salt the water. a LOT. Remember that most of the salt will get thrown out when you drain the pasta. Ideally, the water should taste as salty as sea water. Pasta cooked in unsalted water tastes like cr*p.
    3. Use LOTS of water. Use the largest pot you have, and make sure the pasta has lots of room to move.
    4. Keep the water boiling hard the whole time you cook the pasta.
    5. Take the pasta off the fire BEFORE it’s fully cooked. The pasta will continue to cook for some time after you drain it.
    6. For FSM’s sake, don’t cook the pasta until it’s mush. It should actually still be a little too stiff when you drain it (see point 5) so that after it’s finished cooking, it will actually be al dente.
    7. Use sauce, olive oil or butter to keep the pasta from sticking, and never, EVER rinse it. You’ll be washing away most of the flavour.

    I’m only 1/8 Italian, but cooking pasta the right way is the one thing that the family kept alive (that and the art of arguing at the kitchen table!).

  7. Funkydebunker says:

    It took me years of trying to cook and serve pasta the “right” way, and found that in order to cook pasta for a LOT of people, you had to do almost the opposite . Yes, pasta should be partly cooked, but then in bulk cookery you would set aside the pot with a lid, and let it finish cooking itself. Then before it was too cooked it had to be washed and drained in cold water, and stored in fresh cold water until you were ready for it. By the time you were ready, the pasta will have absorbed exactly the right amount of water. Then you either re-heat the pasta in boiling water, or finish cooking it in a pan with some sort of sauce. So boil it in well salted water- by the time you serve it most of the salt is gone.

  8. Thanks for all the comments.
    I cook a lot from scratch and don’t add much salt to things, as a result, I find most canned/packaged sauces and soups are salty enough for my taste already. I find that pasta ends up with far more flavour if I wander over to the spices and throw some of those in with the water.

    • DR says:

      The real answer to that is: don’t use canned sauces… I can make a decent tomato sauce from scratch in a pressure cooker in 25 minutes. Non-tomato sauces usually take even less time. Aglio e Olio is instantaneous: just add olive oil and chopped garlic, red pepper flakes if you wish, and salt and pepper to taste. The sauce being salty does not change the fact that if you don’t salt the water, the pasta itself will be bland, and no sauce can cover that up.

      You’re cheating yourself of good food here… Makes me sad…

    • Paul says:

      I actually can’t use a canned sauce, because they have so much salt in them. I prefer a homemade sauce, with no salt – because tomatoes already taste good by themselves – and lightly salted pasta.

  9. Tim says:

    I concur with the above comments. Adding salt is for flavour, not to make the water boil faster or cook quicker.

    One thing worth noting however, is that adding salt to an already boiling pot WILL cause it to boil more vigorously, for a couple of seconds. I believe its related to nucleation; adding a bunch of tiny particles to the water provides a bunch more nucleation sites for the vapour bubbles to form, until the salt eventually dissolves.

  10. Ken says:

    My wife and I were having an argument about this a several years ago, and my Father the cook settled it. They add salt to water for pasta for flavor. I always thought as you did, helps water boil faster.

  11. David Grant says:

    I’ll also chime in, it is for flavour…although I admit that years ago when I was much younger I did think it had something to do with affecting boiling point just like salt on ice affects melting point (at least I assume it does…).

    Pasta with a good amount of salt in the water tastes SO much better than without. Of course you can add salt via the sauce too, but I think some in the noodles and some in the sauce is perfect.

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  • Marion Kilgour

    Marion is a mechanical engineer, and also works to promote critical thinking and scientific literacy through local skeptical and atheist activism in Edmonton, Alberta. Marion especially wishes to encourage girls to consider science or technology-based careers, and is involved in the University of Alberta's Women in Scholarship, Engineering, Science and Technology (WISEST) project.