Why does ice you buy from the store have holes in the middle? Also, why are they more clear than what a home icemaker produces?
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Here’s a YouTube short video of those things at work:
# [This is how ice making machines work](https://youtube.com/shorts/xbH2XH5Pxmo?feature=share)
The freezing cold refrigerant is run through a bunch of cold “fingers” on which the ice forms. They reverse the operation briefly to get the ice to melt off of the fingers.
The ice is much more clear because the ice is freezing inside-out. When ice forms, all of the dissolved gases and minerals get pushed away from the growing ice crystal. Your typical ice cube frozen in your freezer freezes outside-in, and this pushes all of the impurities and dissolved air into the middle, causing there to be a cloudy patch in the middle of the ice cube, but when ice is formed on these cold finger style ice makers, the ice freezes inside out, so the inside is really clear, and the impurities are pushed into the surrounding water. When the water basin is lowered away from the cold finger, all you’re left with is clear ice.
Any cloudiness or inclusions in this kind of ice only form because the freezing is happening so fast that impurities get trapped at the boundaries between individual ice crystals.
(Mono-directional freezing is how fancy bars make large clear ice cubes as well. They have gadgets that let the ice freeze top-down so all the impurities and dissolved air gets pushed out the bottom.)
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