system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: We all know that water freezes at 0°C. But does it freeze harder at lower temps?

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?
gpt
ice cream is typically made by churning the fat sugar water mixture to incorporate air as it freezes. this prevents ice crystals from forming above a certain size. a good ice cream is technically a frozen foam with millions of microscopic ice crystals and should feel like snow even at -21C.

the problem happens when storage is actually not as cold as reported. warmer than -18C, ice crystals can start to fuse into large crystals over time or even over several cycles of taking it out into the room for a few minutes.

same thing happens with snow. if it cycles through warm periods eventually the powder snow becomes rock hard.