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.