Boiling water with salt

PEU · Jan 23, 2006

Yesterday I had a cullinary discussion with my wife, we were cooking pasta, spaghettis, so I filled the recipient with water and put it on the flame to boil it.
I was about to put some salt on the water, so I don't forget later, when wifey said: don't put the salt now, wait until it boils.

so the question is:

Does water change its boiling point when you add salt (NaCl) ?
If it changes which is the new boiling point?

thanks

Pablo

jtice · Jan 23, 2006

I dont know how much, but yes, I think it changes.

I add just a bit of cooking oil to keep mine from boiling over in a white bubbly froth.

~John

yuandrew · Jan 23, 2006

Salt raises the boiling point

http://antoine.frostburg.edu/chem/senese/101/solutions/faq/boiling-pt-elevation-experiment.shtml

PEU · Jan 23, 2006

after googling a while I found this:

For pure water, the boiling point is 100 degrees Celsius (212 Fahrenheit) at one atmosphere of pressure, and the melting point is 0 degrees Celsius (32 degrees Fahrenheit) at one atmosphere of pressure. At lower pressures (at high altitudes, for example, in Denver, Colorado), the boiling point will be perhaps a couple of degrees lower.

For saltwater, the boiling point is raised, and the melting point is lowered. By how much depends on how much salt there is. I'll assume the salt is sodium chloride, NaCl (table salt). The melting point is lowered by 1.85 degrees Celsius if 29.2 grams of salt are dissolved in each Kg of water (called a "0.5 molal solution" of salt. The Na and Cl dissociate right away when dissolved, and so for a 0.5 molal solution of salt, there is a 1.0 molal concentration of ions). The boiling point is raised by 0.5 degrees Celsius for water with 29.2 grams of salt dissolved in each kg of water.

If your concentrations of salt are different, then you can scale the boiling point elevation and melting point depression predictions directly with the concentration.

These numbers come from the CRC Handbook of Chemistry and Physics.

Source: http://van.hep.uiuc.edu/van/qa/sect...Evaporating_and_Condensing/20030104203955.htm

It raises the temperature, but the difference is negligible, so I preffer to put salt before boiling, than to forget and eat nonsalted spaghettis, they taste dull that way

Pablo

Chris_Medico · Jan 23, 2006

PEU said:
Yesterday I had a cullinary discussion with my wife, we were cooking pasta, spaghettis, so I filled the recipient with water and put it on the flame to boil it.
I was about to put some salt on the water, so I don't forget later, when wifey said: don't put the salt now, wait until it boils.

so the question is:

Does water change its boiling point when you add salt (NaCl) ?
If it changes which is the new boiling point?

thanks

Pablo

The main reason to put it in when the water is boiling is to keep the salt from sitting on the bottom and causing pits in your stainless steel pot.

The chloride side of salt is very damaging to stainless.

magic79 · Jan 23, 2006

I'm not sure I agree with your assessment, Chris.

As the excerpt from the Handbook of Chemistry and Physics states, salt dissolves immediately (even in cold water) forming and aqueous Na+ and Cl- solution. It will continue to dissolve until the solution is saturated, determined by water temperature. Unless you put a lot more than a couple of tablespoons in, it will rapidly dissolve and not sit on the bottom as NaCl crystals.

Once on the stove, convection currents almost immediatly begin circulating the aqueous solution, thereby minimizing the contact of the quite weak concentration of Cl- ions.

So, I don't think you will get an accumulation of either undissolved salt or chlorine ions on the bottom. Since the chlorine ions are lighter than water, I think they would tend to rise without convection currents anyway.

watt4 · Jan 23, 2006

try it.

Chris_Medico · Jan 23, 2006

magic79 said:
I'm not sure I agree with your assessment, Chris.

As the excerpt from the Handbook of Chemistry and Physics states, salt dissolves immediately (even in cold water) forming and aqueous Na+ and Cl- solution. It will continue to dissolve until the solution is saturated, determined by water temperature. Unless you put a lot more than a couple of tablespoons in, it will rapidly dissolve and not sit on the bottom as NaCl crystals.

Once on the stove, convection currents almost immediatly begin circulating the aqueous solution, thereby minimizing the contact of the quite weak concentration of Cl- ions.

So, I don't think you will get an accumulation of either undissolved salt or chlorine ions on the bottom. Since the chlorine ions are lighter than water, I think they would tend to rise without convection currents anyway.

If you spread the salt around the surface it most likely won't make it to the bottom in any real concentration. If you pour it in a stream it will make it to the bottom for sure.

It takes very little to damage stainless. Unfortunately I have plenty of experience with this. And with stuff more expensive than cooking equipment.

cratz2 · Jan 23, 2006

Are you trying to tell me that if I run 6 oz of luke warm water in an 8 oz glass and then add .5 oz of salt, it will dissolve immediately?

I don't think so.

When I worked as a kitchen trainer, most restaurants that had actual kitchen manuals all stated to bring a liquid to at least a soft boil before adding salt or salt-heavy seasonings. I asked the know-it-all regional quality manager (at a large chain casual Mexican restaurant) and he quickly replied that the tilt we cooked the beans and rice in cost $7,000 and it would quickly develop rust if salt was allowed to sit on the surface for long.

I guess it comes down to this... if you have a $35 set of pots and pans, then add the salt whenever the notion strikes.... If you use a $400 set of pots and pans, I'd personally take better care of them.

chmsam · Jan 23, 2006

Yes, the salt raises the boiling point, which can be a good thing for cooking.

The amount used in cooking, usually about one tablespoon per quart of water, will take quite a while to pit a quality pot. Since it is not all absorbed into the food being cooked, while it will raise the sodium content, I kinda doubt it's going to be too high in the finished dish.

I, too, use oil in water for pasta to keep the water from foaming and to keep the pasta from sticking quite as much. This is the way I was raised to do it, and there may be no scientific purpose to it, but what the heck, it works for me.

twentysixtwo · Jan 23, 2006

I add salt just before adding the pasta, so yes, it's typically boiling. As far as the corrosion thing goes, if you add your teaspoon of salt and stir vigorously, the corrosion should be negligible as the salt should dissolve almost immediately (with the stirring, that is)

I used to add oil to my pasta, but according to Alton Brown, this also prevents sauces from sticking to your pasta afterwards. I just use a larger pot and watch it more carefully to prevent boil-overs.

chmsam · Jan 25, 2006

Ah Ha!! The trick with pasta and sauce is to cook the pasta al dente, drain it well, and then warm it in a skillet. Then add the sauce long enough to warm the sauce through. Much less excess moisture in the pasta and the sauce tastes and adheres better. Only takes about 3 to 5 minutes.

Boiling water with salt

PEU

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