# Question re: physics of ice

BobB Oct 17, 2011 07:36 AM

We have plastic ice cube trays and I've noticed that when I refill them immediately after emptying them (while the tray is still very cold), the cubes that form stick to the plastic and are very hard to remove, cracking and breaking in the process, whereas if I rinse out the tray and let it warm to room temperature, then refill it and freeze it, the resulting cubes come out cleanly and easily.

Anyone know why this is? Is there some kind of bonding effect between water and cold plastic?

1. How interesting. I wonder if I can duplicate this with a squirt of hot water before refilling.

1. Not something I'd ever heard of before. Interesting. I'll take a TOTAL shot in the dark here:

I suspect the biggest difference would be in terms of how warmer plastic has expanded more than cold plastic. My guess at what's happening: warmer plastic contracts as it cools in the freezer while water actually expands as it freezes - this causes ice cubes that started in a warmer tray to 'settle' a couple times while they're freezing, which in turn loosens them from the sides and bottom of the tray. Ice cubes started in a colder, already contracted plastic tray would do less 'settling' and thus could bond tightly to the plastic in spots, which of course makes them harder to remove.

Really though - I don't know why this happens. Mateo's hypothesis makes decent sense as well.

1. re: cowboyardee

Both theories sound reasonable to me. Thanks!

2. Conjecture: (chemists please speak up) if you pour a little gin in each compartment before adding water, the water (with a small amount of gin) will then freeze out of the mix first, leaving the remaining gin behind in liquid form which will allow the cube to slide easily out!

1. Shot in the dark here... but might it have something to do with the insulating properties of plastic?

If your plastic tray is ice-cold when the water is loaded, it might allow the temperature to move faster through the actual tray, versus warm tray which would take a little while to cool down before allowing the cold to move through the tray as effectively. What you might get is that when your ice is freezing from "top down" with a warm tray, the surface freezes first, producing more expansive force on the tray once frozen... whereas when you start with a cold tray, you're getting more even freezing from the size and the top, allowing less pressure to force the expansion of the cube out, and thus the crystals form up.

I wonder how we could test this...

2 Replies
1. re: mateo21

I'm not a science type, but this makes perfect sense. I may try this experiment this weekend.

1. re: mateo21

Going from "warm tray" to "cold tray" in any freezer is a matter of minutes (more likely "minute"). The tray will be freezer temp before the water is anywhere close to freezing.

2. This is interesting, the other thing I noticed is it only seems the bottom tray ( I stack three trays) has this problem with the ice cracking. Does this happen to you as well?

6 Replies
1. re: andieb

No - we also have three trays and it doesn't seem to matter where they are in the stack.

1. re: BobB

The biggest issues re:variations in ice are impurities in the water, mineral or otherwise. Use distilled water and your ice will be consistent from batch to batch.

1. re: ferret

We always use simple cold tap water (very good water quality here).

1. re: BobB

same here. We're both in the same area...

1. re: BobB

I'm not suggesting that you use anything different, just that you'll see greater inconsistency between batches with tap water because it's not a consistent product. Using distilled will eliminate variation from batch to batch.

1. re: ferret

But my question is, why do I get consistently different results when I freeze tap water in cold trays vs room temperature ones?