Stainless steel... or is it? - FineCooking.com

My Recipe Box
Food Science
FOOD SCIENCE

Stainless steel... or is it?

By Brian Geiger, contributor

July 2nd, 2009

There was talk on the Twitters this week about salting boiling water. There are a number of myths surrounding boiling water, including that adding salt will increase the temperature of the water when it finally does boil and similar foolishness. I was all set to debunk this myth, and that's when I discovered something more… sinister.

The advice given was that you should always add salt to water that's boiling, rather than to water that's cold. Inquiries were made by Jaden of Steamy Kitchen as to whether this was true, and I suggested that it was not. Then I heard from people who actually know about these things (i.e. Judy of Divina Cucina).

After a bit of back and forth, it was explained that this happened with stainless steel, specifically. This, of course, is fascinating, and it certainly plausible, so research ensued.

Stainless steel is steel that is at least 12% chromium. Instead of allowing oxygen from the atmosphere to combine with iron to form rust, the oxygen combines with the chromium. Because of the way the molecules combine, they form a thin, thin, layer on the outside of the metal. Technically, this is a stain, but it's a stain that you can't see, which philosophers would argue is no real stain. Even better, the oxygen reacts with the chromium quickly, so that even if you scratch away the invisible stain, it reforms as close to immediately as makes no difference.

This is all well and good, but salt water will react with the film, and it will keep the film from re-forming before other reactions cause visible discoloration. In relatively weak concentrations of salt, such as what you would use for cooking pasta in, this is not a problem. However, if the salt falls to the bottom of the pot and starts dissolving there, you'll have tiny pockets of discoloration where the salt was too heavily concentrated.

If you salt boiling water, the salt will dissolve and spread around before it hits the sides or bottom of the pan, and all is well. Hence the advice.

Warning: sciencey content ahead. If you are content with everything so far, and aren't interested in "competing hypotheses" and "scientific method", then you are free to go. For those wanting a little something extra special with their weekly post, please follow along.

I've heard an explanation that claims that the reason that you boil the water is not to reduce the localized salt content, but to remove the oxygen from the water before the chlorine in the salt has a chance to tie up the chromium atoms. This is a feasible explanation as well, but I don't know that I agree with it.

Fortunately, there is a way to find the truth of this: I will find three new, identical, and preferably inexpensive stainless steel pots.

 

  • In the first pot, I will add boiling water followed by a large concentration of salt. 
  • In the second pot, I will add water that has been boiled, allowed to cool, then add some salt. 
  • In the third pot, I will add water that has been boiled, had salt water added, been allowed to cool, then aerated. 

 

If the pots are inexpensive enough, I will buy a fourth just so I can not do anything to it, thus allowing me to have a proper control condition.

If the theory about salt concentration is correct, the first and second pots should discolor, but not the third. If the theory about the oxygen is correct, then the third pot should discolor, but not the first two. If the second pot is the only one to discolor, then I probably didn't add enough salt to the first pot.

If the first pot discolors but not the other two, then I will be terribly confused, and I probably won't know what's going on.

I've mentioned before, but it's worth repeating: the important difference between science and folklore is that one is better at explaining what happened than another. There are advantages and disadvantages to both methods as a form of explanation. The important thing about science is that you should be able to predict when something will happen, and when it won't. If you can accurately predict both things, then you've got a functioning hypothesis. If you can't predict either of those scenarios, then either your hypothesis is incorrect, or you're not dealing with science.

posted in: Blogs, food geek, water, salt, science, stainless steel, chromium, steel
Comments (6)

TheFoodGeek writes: kelbel917, I've just returned from some travel, so I've not yet had a chance to find the pots to experiment with. I'm concerned, based on what purringcat and Betty_01 have written, that my plan of going with a cheap pot might be a poor idea. I'll have to find a good bargain on some small but quality stainless steel, apparently. Harumph. Posted: 5:01 pm on July 9th

TheFoodGeek writes: Indeed, from a theoretical standpoint, the salt will raise the temperature of water. However, from the perspective of "Should I add the salt before or after the the water is boiling," or even, "Will the salt change how the spaghetti will cook," any concern for the boiling point is foolishness. Not only will it not raise the point any measurable amount, but the changes from the chemicals in the tap water, any sort of water softener you might use, and the eventual addition of starch from the pasta itself will all mix in to have a greater or lesser, but still negligible, effect.

From other perspectives, naturally it means different things and has different effects. From this perspective, it's foolishness. Posted: 4:59 pm on July 9th

Betty_01 writes: The pot that had flecks missing was probably made in China.
I try to not buy any Chinese made products. Definitely feel adding salt to the water helps elevate the boiling temp. Posted: 3:19 pm on July 9th

kelbel917 writes: If I recall correctly, adding salt should, in fact, increase the boiling temperature of the water. This effect is similar to how salting an icy sidewalk causes the ice to melt as the freezing temperature decreases.

Any results on your stainless + salt experiment? Posted: 9:41 am on July 9th

cookieMama writes: Just so you know...adding salt does raise the temp of boiling water. It is known as boiling point elevation and is a colligative property of solutions. You can also decrease the freezing point the same way, which is why you add salt to ice when making ice cream. Now, the amount of salt you add to water for pasta is probably not enough to make a measurable difference if you don't have very sensitive equipment, but calling it "foolishness" makes YOU seem foolish and ignorant. This is a property of solutions that every high school chemistry student should know, and as a biologist and chemist, I can tell you for certain that it is true! Posted: 9:25 am on July 9th

purringcat writes: I recently bought a large well known brand stainless steel pasta pot (with the inside liner)from a box store selling bedding and kitchen goods.

My method of using it was: with the inner pasta draining pot inserted, fill to within a few inches of the rim. Add salt before reaching a boil and then add the pasta. The pasta came out fine but the pot didn't.

The pot not only 'lost' pieces of the stainless coating all over the inside, it stained my new stove with flecks of stainless that can't be removed.

What is a stainless steel pot made of? Certainly not solid stainless steel. Posted: 5:28 pm on July 2nd

You must be logged in to post comments. Log in.

Cookbooks, DVDs & More