salt in ice blocks

Hiya Tojo,

Adding salt to water lowers the freezing point. The old timers used to say that sprinkling salt over the ice made it last longer, I don't know if it was true or not, but certainly the oldies used to swear by it. I guess it's a case of knowledge lost to a bygone era.
Keep the shiny side up.
Ferris

Commercial fishermen make a slurry by adding ice to seawater. It keeps the fish at a temperature below freezing but not frozen, ie fresh. Adding salt to ice does indeed lower the temp but I think you will have trouble freezing salt water.

Tojo, Aaah an interesting and much often debated question by chefs.

We have our display trays or ingredients loaded up on ice and some prefer to sprinkle salt over the ice, it initially melts the ice then quickly refreezes turning the crushed ice into a solid conglomerate. Basic thing to remember is that it melts the ice....

After many vociferous and heated debates we timed it with salt and without, the unsalted lasted considerably longer. NB picture the red faces at the bar buying beers!

As to wether salted frozen water will last longer, salt water needs a lower temp to freeze so therefore the converse applies, it will also melt earlier than water.

I beleive this theory is proven : in colder climes than ours where salt is spread on paths, roads etc to melt the ice.

: by the ocean, when it does freeze, (pack ice etc) the concentration of salt in the frozen particles is less and resulting unfrozen now saltier ocean water drops lower in the ocean creating a cycle of currents.

: in a salted ice cream I tred to make last month that i couldn't even get to freeze!

I'd be very interested if you find otherwise.

frozen salt water is difficult to keep "solid" and tends to get slushy when thawing. We used to use either for chilling longline tuna and swordfish. But if you make a saltwater slurry with saltwater ice, the temp will be around -4, enough to freeze the extremities of a tuna and the Japs would devalue the fish as they take samples from the tail area for inspection.
A slurry made with freshwater ice, the ice stays solid til thawed. Saltwater ice it slowly goes slushy.

Hey Tojo
A funny question this one.....
In Canada they use a mixture of gravel and salt on icy roads to melt the ice and give extra grip

I have one of those wine cooler type eskies. It has space for 4 bottles of wine seperated by shaped containers that you fill with water and freeze to keep the wine cold.

One of my brothers intelligent friends has the same esky. He used to put salt water in his on the basis that it froze colder and therefore kept the wine cooler for longer.

I fill mine with fruit cordial (cottees, golden circle etc) as the cordial melts it provides an icy cold drink for the kids. It still keeps the wine well and truly cold enough for me.

I figured that if you fill it with salt water it's useless when it melts and the temp differences are so minimal that in reality they don't matter

That's my 2c worth.

Duncs

It's one of the great mysteries of life LOL
I don't know about freezing salt water, but I have added salt to ice twice with interesting results.
The first time was on Christmas day a couple of years ago. An average size esky, beers, ice to cover and loads of salt. No idea how much but it was our first attempt after hearing the theory. At a guess; 500gms. The next day, after an overnight low of about 25c or more, the ice had become one solid block that had to be broken up to access the beers.
The second time was just recently while in Tenterfield and Glen Innes. I had put 500 gms of salt over 5kgs of ice in a 95L ice box. The ambient temperature over the next few days was between 5c and 15c. The ice turned to slurry but still solidified in clumps. We had vegies in a large tupperware container to keep them out of the water/ice and we had to throw some away because they froze! Also some things in jars etc in the slurry froze, like yoghurt, jam etc.
I've never experienced this before. The ambient temperature wasn't blow zero.
There is no way a slurry of 'normal' ice will freeze things.
Not a scientific experiment, draw your own conclusions.

Hi Tojo

I wouldn't rip into the bosses supply , salt costs so little in big bags these days.
Some swimming pool salt from supermarkets is down to $6 for 25kg.

Everyone agrees that adding salt lowers the temperature that the mixture freezes at and this offers the potential for it to last longer provided you put the cold energy in first (I.E. you actually freeze the mixture in your fridge).

But - never use it myself though as that's not really the mission.

My mission is instead to keep the food fresh, and the key point about ice / dry ice and various mixtures is that the cold energy is nearly all concentrated around the mixtures freezing temperature.

So if its ice this is zero , and if salt ice it might be -15c (depending on concentration). Dry Ice around -70.

So if I put my lettuce/ tomato's in a esky at zero they will survive without damage.

If I put them in salt ice esky at -15c they will be damaged etc.

This is the crucial point - even if I freeze a water ice block to -15 in fridge if does
not hold a lot more cold energy than if it was at -5 and will rapidly come up to
it nominal freezing temperature 0 and then be safe for the food I need to keep fresh.

Robin Miller

G'Day Tojo,

Been through all this, not worth the effort. Best bet is to find the size container you want and freeze this as low as it will go. Out of interest, if you pack some of those techni-ice type packs around the container in the freezer you can actually get it to go lower than the freezer setting itself.

Cooling efficiency occurs at "phase change", that is how your fridge works, compressor changes gas to liquid, as liquid turns back to gas, cooling occurs.

So, in your esky, put in the size blocks you want. As the ice in the containers turn to water put the water in with your favourite scotch, boubon, etc and enjoy a cold drink as well. (Cordial for the kids!)

Adding salt will do little more than waste the water after the ice melts

Regards

Rolande

There was a long discussion about this on this forum a few months back and came up with some good answers. Basically - adding salt to ice is useless. However adding salt to water that you freeze will keep the temperature lower but not really longer.

I'll have do a search for you when I get some time.

R.

Thanks for all your responses seems like its not really worth the effort , but how do you stop large blocks from ballooning out when freezing them, sometimes they dont but more often than not they do and tend to crack and break.
thanks heaps Tojo

To stop the ballooning don't completely fill your container(leave it an inch or so from the top). Then squeze the container to push the water up to the rim, then screw the cap on. As it freezes in the freezer and the liquid expands you get a normal shaped container.

There is a very good post on here somewhere, type in ice brick or salty and see what comes up. It explaines the physycs of adding salt to water. Basically yes it does lower the freezing temp of water (we all knew that). So add the salt before freezing your brick. You will need a good freezer to get the temp down low enough. The beauty of doing this is that it keeps the temp low longer even though the solution has melted. The reason being that to increase the temperature of the ice takes less ambient heat than it does to increase it when it is a liquid. So if you have a liquid at -10c (which you can achieve by adding ice) it absorbs more heat energy to bring the temp up one degree than normal ice at -10C (approx twice as much from meory). This keeps the temp lower longer. Also it takes far more energy to convert ice to liquid, with a salt soltion this has to happen at far lower temps, helping to keep the temp lower longer. This is probably a poor explanation, search the threads to find a much better one. The guts of it is that adding salt, then freezing the solution does work.