I’m wondering if anyone else has ever noticed this and if they have an explanation for it.
I make ice cubes in two plastic trays that I stack one atop the other in my freezer (I know, too cheap for a 'frig with an automatic ice maker.). Whenever I go to remove ice from the trays, the cubes in the top tray always pops out MUCH more easily than the cubes in the bottom tray. It usually requires a good deal of “torque” or some tap water run across the back of the tray to free the cubes in the bottom tray. It doesn’t matter which tray is on top and I’ve observed the same thing with different trays and different freezers. My fianceé has also noticed the same thing at her home.
I think I now understand why this happens, but I don’t want to influence anyone else’s thoughts. I’ll post my ‘explanation’ later. For now, I thought I’d check to see if anyone else has observed and pondered this weirdness.
Thanks
I have also observed this and I think the answer is quite easy: the colder the ice/tray the harder it will be to remove the ice. the bottom tray is colder as nearer the refrigerant – it also freezes faster
In my freezer, the cold air comes out of a vent in back, near the top, so the bottom tray isn’t near the refrigerant. I don’t know how much colder it is simply by being a few cm. lower than the top one.
But I don’t use ice, so I’ve never noticed the phenomenon.
WAG: If you have an autodefrost freezer, I’d think it’s the freeze-thaw cycle that’s responsible. Since ice cubes freeze from the top down, perhaps they don’t stick to the bottom of the tray very well. When the defrost cycle comes on, the outermost layer of each cube melts and perhaps will then stick better to the tray.
Sure, I’m all for moderation – as long as it’s not excessive.
I think I’ve got this one. It’s not temperature differential, or the defrost/thaw cycle. The top tray is exposed to the air flow in the freezer, the bottom tray is not. The ice in the top tray sublimes at a much faster rate than the ice in the bottom tray. As the cubes get smaller, they tend to lose adhesion to the tray, and will just fall out. So give us your guess.
Thought about and discarded sublimation after a look at the stacked trays in our freezer at work (yes, the bottom tray’s cubes were stuck!) revealed equal amounts of shrunk cubes in each. However, there’s no food in this freezer to block air movement, so a full freezer may have more sublimation in the top trays.
Sure, I’m all for moderation – as long as it’s not excessive.
I had this problem when I stacked four trays together. I took care of the problem by arranging my four ice trays in two stacks of two. I’m not sure what this says about the above theories, but as far as I am concerned, the end justifies the means.
Well, I guess I started this, so I’ll give my theory.
Like some of you, I’d originally thought that maybe the bottom tray was a little colder, but it seems very unlikely to me that the small temperature differential that might exist could account for what is really a big difference in the nature of the ice cubes .
So, I examined the ice cubes from the two different trays and saw some real differences between the top and the bottom tray cubes.
The top cubes had translucent centers (fine ice bubbles, I’m fairly sure) in the bottom 1/2 or 1/3 of the cubes. Also, the bottom and some of the sides of the top tray cubes were rough, kinda pitted.
The bottom tray cubes had the same gray, translucent centers, but they were more towards the top 2/3 or so of the cubes. The bottom and sides of the cubes were very smooth, not at all pitted like the top tray cubes.
So, here’s what I think the explanation is:
You can think of the two stacked trays as essentially a single mass of water that happens to be interupted by the ice cube compartments. As it cools and begins to freeze, it freezes from the outside towards the center. As freezing progresses, the dissolved air becomes progressively more concentrated in the still liquid center of the mass, i.e., towards the tops of the bottom cubes and bottoms of the top cubes. This explains the offsets of the gray, translucent ‘centers’ in the cubes. The pitted nature of the bottoms and sides of the top cubes comes from, I’m fairly sure, air bubbles that are trapped against the walls of the cubes. The presence of the trapped air bubbles aganist the bottom and sides of the upper tray cube walls reduces the amount the surface area of ice that is adhered to the tray walls, resulting in cubes that pop out more easily. The gray, bubble rich ‘centers’ of the bottom tray cubes are displaced towards the tops of the cubes, where the bubbles are not in contact with tray wall, so the bottom cubes stick more to the trays.
I think this is right, but I’d sure like to hear anyone else’s thoughts on this.
Have you noticed if the two trays are kinda stuck together when frozen? Perhaps they bond together and change the structural properties of the two trays during the freezing process. Once separated the bottom tray could change its shape and clamp down tighter on the cubes.
watch what you say
or they’ll be calling
you a radical,
a liberal,fanatical
a criminal…
Strato, while the trays do freeze at different speeds, I still believe it is solely a matter of temperature.
I own a boat and need tons of ice. Being cheap I figure I can make my own ice rather than buy it so I routinely make ice emptying the trays in a milk crate several times a day whenever I happen to be in the kitchen. believe me, I have some experience in this and have given it some thought.
my conclusion is that it is strictly temperature. if I do not give the trays enough time to free hard, then both will empty easily. If I give them more time, then the lower one is harder to empty and noticebly colder (fingers stick more) and if I give even more time (overnight) then both are just as hard to empty and, in fact, the cubes tend to break rather than come out in one piece.
you may wanna try this: after the trays are frozen, swap them and leave them a few hours and see what happens. Do a blind study. cn you tell which one froze oon top if I switch them randomly just by how hard they are to empty?
Sailor,
You raise some interesting ideas. I’ll have to do some tests. Also, since posting the note I was thinking that I should try boiling the water before putting it in the trays and then see what happens.
Heating the water, I believe, drives off most of the air that’s dissolved in it (This, I’m told, is the explanation of why hot water pipes freeze before cold water pipes. I always thought it was some kind of old wives tale, but I’ve been told on good authority that hot water pipes do freeze first and that it’s because the air has been driven out by heating and that water w/ little or no dissolved air freezes at a higher temperature than well aerated water.)
If my hypothesis is correct, then there shouldn’t be much difference between the trays if there’s little or no gas dissolved in the water. Also, I assume that if there’s little/no gas in the water, then there should be little/no gray translucent ‘centers’ to the cubes.
If this works, then we’ll have to start boiling the water for ice making so we can have nice crystal clear ice cubes for our martinis, or scotch, or whatever.
I’ll try it out tonight and will report back tomorrow.
Tried boiling the water first and no real significant difference. Upper tray cubes still popped out easily and bottom tray cubes were difficult to remove. There were still the same GTCs, so there appears to have still been plenty of dissolved gas in the cubes.
I did another experiment where I froze the water in the two trays and then restacked the trays after freezing, allowing them to equilibrate overnight. Ice from the tray that was originally on the bottom was still much harder to remove, so this says to me that it’s not a temperature differential between the two tray positions. It seems pretty clear to me that the answer to the dissolved gas and where the gas gets trapped in the cubes during freezing.
I’ve noticed this too. My thoery has nothing to do with bubbles, but the direction of freezing: In my freezer, cold air is blown over the top of the cubes, so the top of the top tray freezes first. As the freezing works its way down, the ice expands and is pushed up the tapered container as it freezes. Only the bottom of the upper cubes are “attached” to the tray after they freeze.
The bottom tray freezes from the outside. So the first thing to freeze is a thin layer along the outside edge that adheres to the ice tray. Expansion pushes the water level higher. Most of the ice is adhered to the tray when the freezing is complete.