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"Are the products in our home freezer actually at different temperatures?"

Dear Anne and Sue,

Are the products in our home freezer actually at different temperatures? I read an article that said ice creams and sorbets are actually physically colder than just plain frozen ice water. Is this true? Isn 't everything that comes out of the same freezer at the same temperature? Or perhaps a liquid stops getting colder once it's in a solid state?

Regards,
Brian In Victoria BC (Vancouver Island)

 

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Hi Brian - and Welcome to the Science of Cooking.

Your question has prompted some interesting discussion - just the kind of dialogue we encourage on the Science of Cooking website. We were (rightfully) challenged on our original answer by audience member Sami, so we called on Paul Doherty, Senior Scientist at the Exploratorium for clarification. The following revised answer includes both Sami's and Paul's expertise. Thanks to you both for your valuable input.

Freezing point is the temperature at which a liquid changes to a solid. As soon as you add a substance (or solute) that dissolves in the liquid portion (or solvent) of the food, the solute physically interrupts the structure and changes the freezing point. Note that in order to change freezing point, the solute must become evenly distributed throughout the liquid. It doesn't precipitate out, nor can it be filtered out. The two most common ingredients in cooking that affect freezing point are salt and sugar.

Sugar lowers the freezing point of water, which makes frozen desserts fair game for changes in freezing point. Most desserts freeze between 29.5 to 26.6 degrees F (-1.4 to -3.0 C) depending on the concentration of sugar. To balance their higher proportion of acids (which give flavors such as lemon, raspberry, etc. their tang) sorbets and ices usually contain a higher proportion of sugar than ice cream and ice milk. And of course to remain frozen they must remain at these colder temperatures.

Not a problem though, as the recommended temperature for home freezers is 0 F (-18C), below the freezing point of both. Assuming that all parts of the freezer are at the same temperature, both ice cream and the sorbet would eventually reach the same temperature as the freezer.

As they warm up outside the freezer, it makes good sense that on a very hot day, a scoop of sorbet is more refreshing than a scoop of ice cream, because it remains frozen longer.

Salt has an even more powerful effect on freezing point, than sugar. In order for this to happen to a significant degree however, the concentration of salt must be so great that the food is unpalatable. So while salt is unlikely to have an affect on the freezing temperature of foods in our freezers, it does explain why, old fashioned ice cream makers used a salt brine to cool a freezing ice cream mixture.

Regards,
Anne and Sue
 

 

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