Why do I have explosively angry ice cubes trying to kill me?

January 13, 2010 3:27 AM

I'd like to know the physics of why my ice cubes seem to want to kill me for disturbing their freezing.

I drink a lot of diet cola with ice cubes. I have one ice cube tray in the freezer and I often run out of ice and have to use partially frozen cubes. When I twist the tray to facilitate the extrication of the cubes large bubbles form in the remaining unused cubes. Then, when I next go to get cubes and twist the tray some of them explode with considerable violence with bits of ice even hitting the kitchen ceiling.

posted by srboisvert to Science & Nature (12 answers total)

You're introducing a bubble of air to partially frozen cubes. When water freezes, it expands. This means that the bubble inside the cube is getting compressed (the freezing water can't expand outwardly, there's already a frozen skin holding it in), creating little pockets of compressed gas. When you twist the tray, the ice fractures, and these little compressed bubbles act just like a CO2 cartridge in a pellet rifle - rapid release of the gas throws pieces of the ice up into the air, your face, hair, across the floor...
posted by pupdog at 3:36 AM on January 13, 2010

So why does the bubble of air form during the intial twist? It is as if the initial twist causes the air distributed throughout the cube to coalesce into one large bubble.
posted by srboisvert at 3:47 AM on January 13, 2010

Air dissolved in water is forced out of solution on freezing. They normallly tuen ice opaque as they remain as very small bubbles. Perhaps your initial twist allows the initial bubbles to move around and merge but not escape. Then further freezing compresses the the bubbles.

If so I would exect the twisted ice to have fewer larger bubbles and be clear. You could test by freezing recently boiled water which has much less dissolved gas. I suspect ice formed from boiled water would never explode.
posted by Fiery Jack at 4:10 AM on January 13, 2010

Fun. A freezer science project. I'll report back.

I also on occasionally get the climbing ice fingers that were talked about in previous askme.
posted by srboisvert at 4:17 AM on January 13, 2010

Yeah, the outer surface of the ice freezes first, and harder - twisting jostles up the less-solid interior of the cubes, letting the smaller bubbles coalesce into larger, more energy packed bubbles as they refreeze. At least, that's how I understand what's going on.
posted by pupdog at 4:31 AM on January 13, 2010

Slightly O/T, but may I recommend a second ice cube tray?
posted by domnit at 5:18 AM on January 13, 2010

or keep your rum in the freezer. it won't freeze, and you won't need as much ice.
posted by toodleydoodley at 6:20 AM on January 13, 2010

About where the air bubble comes from, I've often had it happen that the shell of ice isn't solid enough to be air-tight on the bottom part of the cube, so when I pick up a part-frozen cube, it slowly drips water out through the porous sides/bottom. The bubbles that form in the tray are outside air that I let in when twisting the tray opens up the sides of the cube to air. Sometimes I can see the little track of tiny bubbles rushing in from a particular hole in the side of the ice shell.
posted by aimedwander at 6:38 AM on January 13, 2010

You are right aimedwander. I performed the boiled water test as well as making closer observations of what happens on the initial twist with partially frozen ice cubes. It appears that air rushes in from outside the cube when I twist the tray. This was more obvious with ice cubes formed from previously boiled water because the cubes were much clearer even after the twist so I could see the air moving into the center of the cube.

domnit, I used to keep three ice cube trays but I found that it used up too much space in our limited freezer space and also had problems with stacked trays freezing to one another. Ice cube freezing time also helps keep my rampant consumption of artificial liquids in semi-check.
posted by srboisvert at 7:49 AM on January 13, 2010

Not related to why, but an ice cube tray with a rounded bottom would help your problem. You can easily remove single cubes by pressing on one side of a cube.
posted by Feantari at 10:07 AM on January 13, 2010

You could also get silicone ice cube trays which shouldn't require twisting, just popping them out.
posted by chairface at 4:19 PM on January 13, 2010

Please allow me to change one word in the conclusion of your question:

large bubbles form in the remaining unused cubes. Then, when I next go to get cubes and twist the tray some of them implode with considerable violence with bits of ice even hitting the kitchen ceiling.

As aimedwander points out, the bubbles are air bubbles. I think when you put the tray back in the freezer, the shell of the bubble freezes to air tightness before the air-- which is initially at room temperature-- has a chance to cool all the way down, so that when the air is completely cooled, a partial vacuum forms inside the bubble, just as when you take a hot jar out of the dishwasher and tighten the lid while it's still hot.

Then, when you get the tray out again and twist to release, one of the bubble vacuums occasionally implodes and sprays ice all over the place. If one of the bubbles pops just right, it seems possible to me it could even kick the cube out pf the tray.
posted by jamjam at 9:05 AM on January 14, 2010