Why Ice Cubes Turn White in the Middle

Break open a store-bought ice cube and, just beneath the surface, you'll almost always spot a snowy white patch at the center. The edges stay clear, but the inside clouds over in a milky blur.

That cloudy core is packed with air. When water begins to freeze, it starts on the outside and pushes the dissolved gases, oxygen and nitrogen, toward the center. Liquid water hangs onto these gases without trouble, but ice does not. As the ice forms a solid structure, it squeezes out anything it doesn't want to include, like how a growing salt crystal leaves dirt behind. Soon the gas is trapped at the core, left with no way out as the ice thickens all around it.

In natural lakes and ponds, the story changes. There, water freezes from the top down, so gases can bubble up and escape into the air. An ice cube tray chills the water from every side, so the freezing front closes in on the middle. The trapped gas gets forced out of the water and forms tiny bubbles in the core. When light hits these, it's scattered in every direction. That’s why the middle of your ice cube turns white, and why snow looks bright, too: millions of tiny surfaces throwing light everywhere.

Big ice blocks for skating rinks stay clear because they're frozen slowly and from one side only. Sometimes, pumps keep the water moving, stopping bubbles from forming. The result is clear, almost invisible ice that lets light shoot right through. At home, though, the freezer works on all sides at once and always leaves that signature cloudy center after a few hours.

Break an ice cube and check its middle, a tangled, cloudy section, often lined with streaks. It’s the frozen memory of every molecule’s path, each bit of air squeezed together by the everyday chemistry of home freezing.