My freezer is set at -21°C (-6°F) and tubs of ice cream come out hard as a rock and are near impossible to scoop. But if I set it a few degrees warmer, yet still way below the freezing point of water, I can scoop it easily. So, is there such a thing as both frozen and *really* frozen? Conversely, a boiling point is a boiling point, I believe. Heating water to a temp above 100°C gets you the same steam that you got at 100, just faster. Right?
In: 102
Ice cream is a bit of a plastic-behaving substance, so it will be harder at lower temperatures. Depends on the mixture, what is in it, but it is a mixture and not a solution, which is why it has that plastic behavior. It can deform without fracturing. As with most plastic substances, there is a transition zone, a range of temperatures where the material is a solid but still readily deformable.
As to the phase change question, a pure substance will give a pure gaseous version at the boiling point and will not rise above the boiling point until there is no liquid to accept the heat and create vapor.
The big issue with ice cream and freezing is that it is a very impure mixture, so the water ice part of the issue is only a part of the reason for its behavior. The water will (mostly) freeze at a temp a little below 0 C (usually salt in the solution so freezing temp is lower, if I understand ice cream making correctly, which I have never studied or tried so could be wrong). The fatty stuff though solid is not crystalline and not easily made into crystalline substance in the presence of all the water and salts. The fatty compounds can slide past each other, so “plastic” behavior. Have to get really cold to make the fats hard to move.
Latest Answers