Why Do Ice Cubes Shatter Instead of Releasing Cleanly?

"I have heavy plastic ice cube trays that came with my refrigerator," says somervilleoldtimer. "I flex them to get the cubes to pop up enough so that I can flip them out into my glass. Sometimes, but not always, the cubes shatter and instead of having a big cube, I get a bunch of tiny little ice pieces. Why does this happen?"

"You probably just need to replace the trays," says gilintx. "When ice trays develop pocks from regular wear, the ice starts to form in the rough little fissures as well. When you go to crack the ice out of the tray, it shatters rather than popping out. I don't think you can find a way to polish the roughness out, so your only choice is to get new trays."

"The temperature in your freezer can vary up to 15 degrees between refrigeration cycles," says Veggo. "'Warm' ice, close to the melt point, is more elastic and flexible. 'Cold' ice is more friable and prone to fractures.... Results will vary for no reason other than when you happen to open the freezer door."

"Sometimes I like having cracked, irregularly-shaped ice," says gfr1111. "Other times, I want un-cracked cubes. My experience is that if you twist the plastic ice cube trays slowly, you create fissures and irregularly shaped ice. If you warm the bottom of the ice cube tray with hot water (as Veggo suggested) [and] just bow the ice cube tray, rather than twisting it; or give it a single, good whack on the counter, you are likely to get whole ice cubes, rather than shattered ones."

Discuss: Why does my ice do this?