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
On a molecular level, ice is ice (there are exotic forms of ice, but none of them will be forming in your freezer). However, the hardness of a substance is based on a lot of structural factors that take place above the molecular, crystal level. Think about snow – its solid parts are pure ice, but is much easier to scoop than hard ice because all of its ice crystals are contained in small, separate flakes which are not strongly attached to each other.
Which brings us to ice cream. Ice cream is not just water, nor is it a uniform structure. There are a lot of proteins, fats, and (if it hasn’t been melted) air pockets in between the water crystals. Even the water itself is not uniform – there is sugar dissolved in it, and there will be tiny pockets with higher concentration of sugar it and pockets with less. The freezing temperature of water changes the more sugar you dissolve in it, which means that the water in the ice cream will not all freeze at the same time or at the same temperature.
What this means is that depending on the temperature of your ice cream, different amounts of it will have actually turned to ice. At extremely low temperatures it’s like solid ice with protein and fat molecules stuck inside it. At higher temperatures close to freezing it’s mostly liquid sugar water held together by a few “threads” of purer ice, which can be easily broken, making it easier to scoop.
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