Cooling a Six Pack With Salt Water

Works great without the mess: Cooper Cooler

My guess is that salt water has a lower freezing point than water, therefore, as long at the ice was close to zero degrees when mixed with the salt you'll have a "blanket" of subfreezing liquid around the cans. This is better than just 0 degree ice because chunks of ice would have limited thermal contact with the beer.

The reason is that adding any impurity to a pure substance will lower it's freezing point. If you look at this another way, it means the ice melts sooner (that's why people salt driveways in winter.) If the ice melts sooner, then it must be colder... that might seem strange until you think about it a while, but try looking at it this way: if the ice melts at something like 5 degrees F, then the misture of ice and saltwater will be at 5 degrees until all the ice has melted... therefore your beer will also be 5 F eventually.

By the way... 0 F is the lowest tempurature Mr. Fahrenheit could get a mixture of salt and ice to go, so he decided that would be 0 on his scale.

I agree, the impurity (salt) lowers the temperature of the ice/water system. This is how: With a closed water/ice system the temperature will stabilize at 32 degrees, at equilibrium, which means that there are just as many water molecules changing state from solid to liquid as there are from liquid to solid. When salt is added, the salt ions slow the liquid to solid change of state, therefore you have more solid to liquid change of state with the resulting energy consumption lowering the temperature of the mixture. So, the beer cools faster because the temperature of the ice/salt/water mixture is lower, resulting in a delta T between the beer and the salt/ice/water mixture to be greater, increasing the driving force for heat exchange. Another trick, is to twirl the can in the ice/salt/water, it will be cold in no time, or frozen. Just like with an ice cream maker.

when i worked on a freezer boat, we put sugar and salt in the dip tank. fresh shrimp were flash frozen. a can of pop left more than a minuit froze. more impurities allowed the freezer to super chill.

The answer to why the salt water is coler is to do with the chemical reaction that takes place between the water and the salt (NaCl). This is an exothermal reaction which by definition is; "A chemical reaction in wich the products have less energy than the reactants." Which means that the reaction draws energy, in this case heat, from the surrounding environment. If I remember correctly the reason for this is the energy levels that the electrons reside at before and after the process of disolving. I can't rember fhe details from 30 years ago but somebody with a fresher understanding of the process may be able to fill in the blanks. This brings me to a party trick that demonstrates the process. If you take a glass of water with ice in it that has reached equilibrium then drape a piece of string over the ice and sprinkle salt over the ice and string the temperature around the string will drop causing the wate to freese and weld the string to the ice making it possible to remove the ice from the water without touching it.

Sorry it is an ENDOTHERMIC reaction an EXOTHERMIC reaction is the opposite.

NaCL + H2O = ???????

What, a chemical reaction between Salt (NaCl) and Water (H2O)? Oh, please! The only thing that happens is that the salt dissolves in the water, turning solid NaCl into Na and Cl ions (electrically charged atoms). That is why saltwater is such a good conductor of electricity. There is NO chemical reaction! No new molecules are created.

HCl + NaOH = NaCl + H20 , now there's a chemical reaction! My high school chemistry teacher actually this, mixing hydrochloric acid with sodium hydroxide and drank the result! Of course, with a complete reaction, indicated by harmless dyes, all he actually drank was saltwater!

Besides which, even if dissolving salt in water takes energy (endothermic), the chilling process would still work even if you added completely dissolved saltwater (no more energy absorption by ionic dissociation) to ice, so your point is totally moot!

There are many descriptions of a chemical reaction but Britannica describes a chemical reaction as "any type of chemical process in which substances are changed into different substances, as differentiated from other kinds of changes—those of position or of form—undergone by matter. Chemical reactions are manifested by the disappearance of properties characteristic of the starting materials and the appearance of new properties that distinguish the products; within the limits of observation, the mass of the products formed is equal to the mass of the substances consumed.". Since we are not talking about position or form and at least 1 property, that of conductivity in this case, has changed then this definition applies to the process of dissolving the salt in the water. Yet another way to look at it is that a chemical reaction requires the breaking and/or creation of molecular bonds and when you dissolve salt in water you are breaking the covalent bond between the Na and Cl. The complete formulae for the reaction is NaCl + H20 = Na+ + Cl- + H20. In any case the reaction/process/call it what you want is ENDOTHERMIC as it absorbs energy from the environment that surrounds it.

As I said above, your point is still moot. The "reaction" of dissolving salt in water has nothing to do with why dissolved saltwater, when added to ice, is a better cooler than a pure water and ice mixture.

I guess things have gotten a little off track. The reason for adding the salt is that it draws energy from its environment, in this case the beer, water & ice. Since before the salt is added the water ice will be around 0 deg C the temperature will fall below zero when the ice is added. The rate of heat transfer between the beer and water is proportional the square of the temperature difference. By lowering the temperature of the water we are increasing the temperature difference and hence the rate of cooling of the beer.

If "things have gotten a little off track", it is because you are heading in the wrong direction. You have a misconception that because salt "draws energy from its environment" as it requires heat to dissolve (not very much actually), that it is the primary reason why adding salt to ice water allows the beer to cool faster. That is wrong. Pay attention this time, I will NOT repeat it:

1. "The rate of heat transfer between the beer and water is proportional the square of the temperature difference." CORRECT (No argument there)

2. "By lowering the temperature of the water we are increasing the temperature difference and hence the rate of cooling of the beer." NOT EXACTLY, by adding salt you have not lowered the temperature of the water, you have lowered the freezing point of the water, thereby allowing the temperature to fall (through the function of giving up heat to melt the ice) without solidifying and therefore "we are increasing the temperature difference and hence the rate of cooling of the beer."

3. "The reason for adding the salt is that it draws energy from its environment..." NO! This is a moot point (it does not matter, makes no difference). We could have added the salt to warm water, made sure it dissolved entirely, no longer drawing "energy from its environment" as the "reaction" would be totally completed, and it STILL would lower the temperature of the ice/water mixture.

Do you get it now? Are YOU back on the right track? If you don't believe me, try the experiment yourself. Dissolve a large quantity of salt completely (so there is no more "reaction" taking place) in a small amount of water and see if that solution doesn't have just about the same effect in lowering temperature as throwing in the dry salt.

Oh, by the way, if you do the experiment, please make sure you measure the temperature of not only the ice/water mixture, before and after adding the salt or the saltwater, but also the before and after temperatures in dissolving the same amount of salt to make the small volume of saltwater. You might be surprised at the result.

If dissolving salt by itself does such a great job of cooling, why don't we have "salt coolers" that work by adding salt, a cheap and relatively plentiful substance, to plain tap water?

I will tell you why, TANSTAAFL!

I will try your recommended experiment but it's 3:30 AM here so it will need to be tomorrow. I just thought of something else that nobody else has mentioned. The rate of cooling is equal to the square of the temperature difference multiplied by the thermal conductivity constant. If adding salt to the water increases the thermal conductivity of the water then the I would expect the beer to cool faster. I have never looked at this nor tested it in the laboratory, what do you think?

Actually, they have almost the same thermal conductivity. Salt water in fact has LESS thermal capacity, so its temperature will increase faster than pure water for the same amount of heat absorbed, or put another way, it takes more heat to raise pure water the same number of degrees as an equal amount of salt water starting at the same temperature. Looking only at that, you might draw the false conclusion that adding salt or salt water would slow down the absorption of heat from the beer in the ice/water mixture, when in fact the opposite is true. That is the danger in drawing broad conclusions from only one set of facts!

I am done with this thread!

I think you are correct about the breaking of the bonds, but the reason that salt water cools better is because the ice/salt water mix will be at a lower temperature than pure ice/water, which remains at 0 degrees C until all water has changed phase to a solid, then the temperature can drop. As many have pointed out.

Additionally, once salt is added to the water and the reaction is complete, you can still sustain the mixture of ice and salt water at a lower temperature than pure water and ice. You should be able to calculate the exact temperature drop for water at the freezing point when you add salt to its saturation point. My bet is that temperature drop would be trivial.

I went to Hilton Head Island several years ago to play golf and go to the Heritage Classic. One thing I found out about Hilton Head is that it must be inhabited by people who like warm beer!

After playing a round of golf one day, my buddy and I stopped at a grocery store to get more beer and ice. I'm the one who thought to get salt.

We got two cold beers each, and one which hadn't frozen all the way, before we had to remove the remainder of the case to thaw out. I used too much salt.

I found out a couple of years later from another friend and professional beer drinker that it takes 7 minutes to cool room temperature, canned beer in salt and ice whereas it takes about 20 minutes to cool them in ice only.

Mythbusters do some weird (and sometimes cool) stuff, but I've seen episodes where they've either failed miserably (as in the hovercraft episode) or disproved a "myth" because they didn't exactly duplicate the experiment (as in shooting a frozen bird at a jet aircraft windshield with a homemade airgun -- the British military engineers used a hypersonic frozen chicken).

Some of the answers above were correct, and some were close, and some were way off the mark, with explanations that sound like nothing but guesswork (like the "chemical reaction").

Shooter was technically correct, but a little bit hard to follow using the terminology that he did.

The short answer is saltwater has a lower freezing/melting point due to the dissolved ions interfering with bonding of water molecules to each other in forming ice crystals. Therefore, pure water can never get colder than 32 degrees, or it would become solid ice. Saltwater can give up more heat to melt the ice and thus lower its temperature without freezing.

Heat normally flows from the warmer material to the colder material, but in this case, at the boundary between the saltwater and the ice, the ice absorbs heat to change its state from solid to liquid, regardless of the temperature (32 degrees or less) that the ice core is at. If there is sufficient quantity of ice, it could even be at a higher temperature (closer to 32) than the surrounding saltwater mixture, and it would still work, so the theory that the ice has to be colder than the saltwater is all wet....or, doesn't hold water....or, leaves me cold...

Anyway, rapid cooling of canned or bottled liquids depends on a large surface area for heat exchange, which happens when it is immersed in ice water or icy saltwater, not when it is surrounded by solid ice cubes. Crushed ice would work better, because it would make more surface contact, but not as good as liquid icewater. However, the saltwater will cool faster because it is at a lower temperature than the pure icewater, due to the constant absorption of heat from the saltwater to the melting ice.

Eventually, the pure water from the melting ice will dilute the saltwater sufficiently that it will reach an equilibrium temperature, that is, just as much ice will be refreezing as is melting, unless more heat enters the system from, say, the outside air or the cans of beer!

"Incidentally, the show debunked a Vietnam-era myth that the best way to cool beer is to bury it in the sand and light a fire over it with gasoline."

Was that a new episode? I guess I missed one. What was the "logic" behind the fire-over-sand theory? I'll bet that would be good for a laugh!

I thought heat always goes to less heat? Since heat is energy the like electrical energy, and salt increases the ability to conduct electricity in water, wouldn't the salt just be increasing the rate at which heat is conducted from the beer to the ice?

NO! Heat is NOT the same as electrical energy. Most metals are good conductors of both heat and energy, and thus the confusion. There are some materials that conduct heat well enough, natural mica(in thin sheets), or thermal grease that allows heat removal from electrical components for example, but are still excellent electrical insulators and some that are great electrical conductors, but conduct little or no heat.

Yes, heat does transfer from high temperature to low temperature. This is called a thermal gradient. Although the saltwater could start out at a higher temperature than 32F, it would quickly cool off (across the thermal gradient between the warm saltwater and the ice) and reach equilibrium at a lower temperature than 32F. Even if the ice is at a higher temperature than the saltwater, it would still pull heat out of the saltwater, thus lowering its temperature, just to melt the ice. There is another temperature gradient, between the ice's surface, at 32F and the lower temperature at its core. Heat then transfers from the higher temperature surfact to the lower temperature core, until the core has reached the melting point as well, then the solid ice is totally melted.

Please refer to my other postings for more details.

In the case of ice and saltwater, there is a thin layer of pure water (melted ice at 32F) between the ice's surface and the colder saltwater. The ice absorbs heat when it changes state from solid to liquid, even if it remains at the same temperature. This is called "latent heat", "heat of transformation", or "heat of solidification". There is a similar "latent heat" or "heat of transformation" when water boils and turns to steam at 212F, but this is called "heat of vaporization". That is why you can get a much worse burn from 212F steam than you can from 212F water, because the steam has more energy, and gives it up (to your skin) on condensing to water at 212F.

HI the whole trail of comments has been wonderful. You all have been correct including the guy talking of the endothermic reaction.
Well replying to your post: Temperature is like electricity in terms of the factors influencing its flow.

1. For heat transfer to take place there must be a temperature gradient as for electric flow to take place there must be a Electric voltage gradient.

2. Infact the conventional assumption of flow of electrical energy is wrong and has been corrected but not fully implemented as most of the designs are based on the conventinal flow of electricity.

Conventional flow: Electricity flows from the +ve terminal to negative terminal.

Truth: Electricity flows from the -ve terminal to the positive terminal.
And do you know where this myth or false conventional electric flow concept was formed from, it was formed in correlation to heat flow transfer in substances.

3. The equation of thermal conductivity is more pertinent to time involved in temperature and temperature losses and not for the transfer itself.

4. Two substances would exchange heat in a heat transfer as long as there is a gradient in response to try and nullify the gradient by their heat exchange.

5. In an ideal case if a substance is at 30C and another at 50C they would exchange heat until they become stable at 40C not taking room temp. into account. In real case the temperature would rest at 37-38C owing to heat losses and time to transfer energy and medium differences and room temperature, thus forming the heat transfer equation. The equation did not come before heat transfer. After analysing heat transfer we came up with the equation.

6. And yes the heat is transfered from the beer bottle to the salt-ice-water mix or ice-water mix. In case it is a metal can then the time required to transfer is far less than the time required with the glass bottle.

7. The endothermic reaction of NaCl and H2O is not too much a factor in temperature reduction. If you talk about Ammonia and water then it is a different story as the energy involved is higher and the temperature is lowered considerably.(ever tried wetting a few ammonia crystals on your palm... it is not recommended as it may cause injury.)

8. Insoluble material and colloids constitute to impurities. Adding salt does not create impurity.
The salt solution(please dont call it a salt-water mix, it is a solution...) helps in conductivity of heat from the beer(higher temperature) to itself.

If the solution is covered or insulated from the atmosphere the result is different than when left open.

There are still a few loose ends that I will comment on later....

Sorry for placing the text so long....

Vishal...

Vishal,

I am not sure if you are replying strictly to my posting(s) or to everyone when you made some of the comments you did, but I NEVER called salt+water a mixture. If I used the term "mixture" it was used correctly when ice was included, as in "ice/saltwater mixture" or "salt/icewater mixture". The implication is that "icewater" includes ice and water, which by definition, can never be a solution, for once the ice is in solution it is no more! As long as solid ice remains you have a mixture.

You also said several things about electricity as related to thermal energy which requires some clarification:

"Temperature is like electricity in terms of the factors influencing its flow."

That may be, but there is danger in taking the analogy too far. Electrical energy flow is NOT exactly the same as thermal energy flow. At least the way I learned Physics. In thermal flow, molecules or atoms transfer energy by their physical oscillations. In electrical flow, energy flows because electrons jump from one atom to the next, displacing other electrons which jump to the next, and so forth.

"1. For heat transfer to take place there must be a temperature gradient as for electric flow to take place there must be a Electric voltage gradient."

Yes, sort of. I never heard of Voltage or EMF referred to as a gradiant, but rather as a differential, more like pressure. Also, transfer of electrical energy requires a complete circuit, not so for thermal energy. Unless you say that a material conducts "cold" as "negative heat" as well as "positive heat" . Even then, you do not have a complete circuit merely two one-way "gradients". To prove this cut a wire anywhere in a simple circuit and energy flow stop. Interrupt a thermal gradient at any point and you will still have energy flow until both sides of the "cut" achieve equilibrium (same temperature) with their respective heat source (e.g. warm beer) or heat sink (ice).

"2. Infact the conventional assumption of flow of electrical energy is wrong and has been corrected but not fully implemented as most of the designs are based on the conventinal flow of electricity. Conventional flow: Electricity flows from the +ve terminal to negative terminal.
Truth: Electricity flows from the -ve terminal to the positive terminal."

Wow, be careful what you call wrong. It all depends on how you look at things. I think my high school Physics teacher said it best: Negative charges flow toward the positive terminal, as the negatively charged electrons jump in that direction, but POSITIVE charge flows towards the NEGATIVE terminal as the "holes" left behind by the jumping electrons.

"And do you know where this myth or false conventional electric flow concept was formed from, it was formed in correlation to heat flow transfer in substances."

Please tell me where you got this gem, or did you just make it up yourself? Positve to negative current flow is not a myth or false concept, it is merely a convention that was chosen for electrical phenomena that were being discovered and measured, not unlike (Warning: Analogy approaching!) the "north" and "south" convention of a magnet and of magnetic fields. Nowadays we prefer to think of "energy" flowing from negative to positive, because that is the direction the electrons jump. There is some small amount of free electron flow in that direction as well, but nearly large enough, nor fast enough, to account for the bulk of the energy transferred.

'Nuff said!

I think Mythbusters got the gasoline cooling legend wrong. The way I've always heard it was the beer would be buried in sand and dowsed with aviation fuel. The fuel WAS NOT ignited, but rather was allowed to evaporate. The fuel evaporates rapidly, thus drawing away heat energy and cooling the beer. Think of putting rubbing alcohol on the back of your hand and feeling the cooling effect as it evaporates. Or simply how sweating cools the body. Same idea, but not sure if it works with beer.

ω

ΗΙ ^{bobby jeo sue}

hmm... that would make sense, thats why we sweat. it evaporates and cools us off. i wonder how cold the evaporating jet fuel would get the beer??

i'll bring the 12 pack if someone else brings the jet fuel

Would regular gasoline cool aluminum cans of liquid if using the method where it isn't lit?

actually the salt lowers the freezing point of water to get it colder faster