Why is factory-frozen ice cream smoother than melted ice cream refrozen in a home freezer?

Answer: Many small ice crystals form

Air bubbles block the cold — Not quite. Air bubbles do slow heat flow and can change how the ice cream melts, but they are not the main reason factory freezing gives a smoother texture. Smoothness depends mainly on how many ice crystals form as the water freezes. Even with trapped air, slow freezing can still leave large, gritty ice crystals.

Many small ice crystals form ✓ — Right. Fast freezing makes many small ice crystals instead of letting a smaller number grow large. Factory freezers also scrape the cold surface and mix the freezing ice cream, which breaks up crystals and spreads them through the mix. A melted pint refrozen at home hardens mostly in place, so it has less scraping and mixing to keep the crystals small.

Sugar stops water from freezing — Not quite. Sugar lowers the freezing point, which helps ice cream stay soft enough to scoop, but it does not stop water from freezing. It also does not explain why factory freezing beats slow home refreezing. A sweet melted pint can still refreeze gritty if it cools slowly.