How can we melt ice in a microwave efficiently?

[I like Serena]

I've noticed that when I put a prefab meal in the microwave, the parts that are frozen over just don't defrost any time soon, even though the rest of the meal gets really hot.
The reason is that the ice structure doesn't allow the polar water molecules to vibrate.
My question: what can we do so that the ice does defrost - and quickly?

I am aware that a modern microwave has a defrost mode, which switches power on and off.
Basically it just means that we give the ice time to absorb heat from liquid water.
That works of course, but it's pretty slow, certainly if the frozen parts are big.

So I was wondering, suppose we add a harmless extra substance to a prefab meal.
One that also has polar molecules and that become embedded in the ice.
As a candidate I've found ethanol, which has a much lower freezing point than water, so it can still be liquid inside the ice.
Would that work to defrost the ice quickly?
And since ethanol has a lower boiling point, isn't it even conceivable that it evaporates (so that we don't become 'drunk' while eating ;))?
Are there other suitable polar molecule substances that might be used instead?

 

[sophiecentaur]

For speeding up the defrosting process without cooking / boiling small regions, there is a system by Pabasonic that's been called "Chaos". It uses random short bursts at full power instead of a continuous low power. I use it and it seems to work. Here is a rather ancient link about it. It's the random nature of the pulsing that does the biz, I believe.
Mixing other substances with your food opens up a can of worms regarding health and safety. Ethanol gives good tax income and would put the price up.
One possibility would be to use metal skewers inside the frozen item. It works well for cooking large 'jacket' potatoes and the skewers could be re-usable with home freezing.

 

[jim mcnamara]

One partial answer: food processors (frozen dinner manufacturers) are very aware of the issue. They try to overcome it with packaging. There are products that have a (usually clear) plastic film that is a steam barrier. And they modify the heating instructions to partially to ask you to remove the film over (example) the dessert-like substance. Low-end products are deliberately deprived of this extra TLC, to save cost, and possibly to coerce you into buying the better product.
Better = more expensive.

Best possible answer: https://what-if.xkcd.com/131/

 

[DrGreg]

One possibility would be to use metal skewers inside the frozen item.

I wouldn't put anything metal in a microwave oven unless it's labelled as being safe for use in microwaves.

 

[Nidum]

Where the food is of a suitable type knead it for a few seconds before microwaving so as to break up the ice and generate lots of cracks and channels for hot liquid and steam to penetrate .

 

[sophiecentaur]

I wouldn't put anything metal in a microwave oven unless it's labelled as being safe for use in microwaves.

It's not a magic process, you know. I think the only necessary thing is to ensure the skewer has a lowish resistance so that the waves are guided in rather than to cause local extreme heat or arcing. A silver wire (2mm diameter) worked very well for me and didn't produce any fireworks in potatoes.
I remember having a Microwave oven (ITT, I think) that had a probe thermometer on a lead that you could insert into the food and the oven would turn off when the object was hot enough. Again, no arcing or excitement.
The problem with conductors in microwave ovens is when they are physically thin and high resistance - like the metallic lines on some crockery. Local high currents along with high voltages is what does the damage.

@Nidum: that's hard to do when the food is frozen solid.

 

[davenn]

Where the food is of a suitable type knead it for a few seconds before microwaving so as to break up the ice and generate lots of cracks and channels for hot liquid and steam to penetrate .

@Nidum: that's hard to do when the food is frozen solid.

Agreed ... as per the OP's first comments ...
Think, frozen microwave dinners ... plastic tray with a clear plastic top ... contents are frozen solid
eg

Dave

 

[Nik_2213]

IIRC, you can get special mats for heating hard-frozen food that will absorb microwaves and get hot enough to thaw the pack from the base.

Don't 'microwave from frozen' single-servings of fries (potato chips) use this trick via a metallised pad in the box ??

Plan_B is to leave hard-frozen packs out for long enough for natural thawing to begin. Time to lay the table, set out plates etc, warn would-be diners, run to wash-room again...

FWIW, when our microwave ovens are running on 'reduced power', they're providing full power at proportionately gapped intervals. Also, we put spacers under meal-packs to give all-around heating...

And, yes, our oldest microwave oven has a plug-in thermometer, plus a 'zap until cooked' program...

 

[sophiecentaur]

proportionately gapped intervals.

Apparently (So Panasonic and others claim) a random length and spacing of power pulses is more effective and provides more even defrosting. As I understanding, the absorption of water is different from the absorption of ice and that's the problem. It's important to keep the defrosting regions different sizes. Hence the Chaos idea.

 

[cosmik debris]

I wouldn't put anything metal in a microwave oven unless it's labelled as being safe for use in microwaves.

I've been saying this for years until one day one of our postgrads put one of those stackable aluminium pots (I forget what they are called) in the microwave. He ignored the howls of derision and heated his lunch. We all said it must be because it doesn't have a lid, he put on a lid and repeated the process. No problem. I'd like to hear an explanation for this. I know things like those twisty plastic things with wire in get extremely hot, red even, but large metal objects?

Cheers

 

[sophiecentaur]

I've been saying this for years until one day one of our postgrads put one of those stackable aluminium pots (I forget what they are called) in the microwave. He ignored the howls of derision and heated his lunch. We all said it must be because it doesn't have a lid, he put on a lid and repeated the process. No problem. I'd like to hear an explanation for this. I know things like those twisty plastic things with wire in get extremely hot, red even, but large metal objects?

Cheers

Just having metal in the cavity is not a recipe for disaster. I have had two ovens with no turntable and they both allow the use of a metal shelf for two layers of food.

 

[CWatters]

If microwave meals really aren't fast enough for your lifestyle best change your lifestyle :-)

 

[sophiecentaur]

If microwave meals really aren't fast enough for your lifestyle best change your lifestyle :-)

 

[PeterO]

I've noticed that when I put a prefab meal in the microwave, the parts that are frozen over just don't defrost any time soon, even though the rest of the meal gets really hot.
The reason is that the ice structure doesn't allow the polar water molecules to vibrate.
My question: what can we do so that the ice does defrost - and quickly?

I am aware that a modern microwave has a defrost mode, which switches power on and off.
Basically it just means that we give the ice time to absorb heat from liquid water.
That works of course, but it's pretty slow, certainly if the frozen parts are big.

We made an ice beaker (sides and base about 6 mm thick) , filled that ice beaker with tap water then placed it in a microwave for a few minutes. We boiled the water without melting the ice.
That would indicate to me that there is no quick way to melt ice in a microwave.
btw: I think a microwave causes the water molecules to spin, rather than vibrate - and in ice (a solid) the molecules can spin.

 

[sophiecentaur]

We made an ice beaker (sides and base about 6 mm thick) , filled that ice beaker with tap water then placed it in a microwave for a few minutes. We boiled the water without melting the ice.
That would indicate to me that there is no quick way to melt ice in a microwave.
btw: I think a microwave causes the water molecules to spin, rather than vibrate - and in ice (a solid) the molecules can spin.

Yes. The different absorptions account for the problem. I think the reason that the chaos works well is that the local regions where melting can happen are probably separated spatially by the mode stirring or the turntable. Having random pulses avoids the hot spots ever being in the same place during a rotation. The process is never as quick as heating water but it is made 'quicker' by this method. Your experiment was an extreme situation and the improvement, starting from deep frozen throughout, is probably more noticeable. (I liked your demo, though)
I agree with CWatters about lifestyle, though! If you look at the cooking instructions forever cooking 'From chilled' and 'From Frozen', there is not a lot of difference in the time; barely a difference of one glass of wine (for the bon viveur) or an extra rant on PF.

 

[I like Serena]

I can actually put many frozen meals in the microwave for 6 minutes and they are done.
It's just that for a number of them that doesn't work due to the ice.
Using the microwave to defrost already takes about 10-15 minutes and then it's still cold.
Is that with the chaos theory solution @sophiecentaur? Or is my microwave just too old?
My current solution is to heat it for 4 minutes, then break the ice as @Nidum suggested, and then finish it with another 2 minutes.

And yes, I could change my lifestyle, but I'm still curious which solutions the manufacturers already apply.
And I'm wondering why they haven't come up with e.g. an alcohol solution, which may be because of health and tax regulations as @sophiecentaur suggested.
Or maybe it just doesn't work.

So to test my alcohol theory, I've put 2 glasses in the freezer. One with whiskey (40%), and one with water.
I intended to put both of them in the microwave to see the difference in melting.
However, the whiskey never froze! Apparently the -15 degrees Celsius or whatnot is not sufficient to freeze it!
It actually still tasted quite good. ;)
So I'll retry after deluting it a bit.

 

[CWatters]

Our standard for frozen means (home made) is 5mins on 900W, decant onto plate/bowl, stir/spread out, 2mins on 900W.

 

[I like Serena]

Now suppose we have a big turkey for Thanksgiving, which is frozen solid, and we didn't take it out of the freezer in a timely fashion.
As I understand it, the recommendation is a couple of days to defrost depending on mass.
How can we still get it prepared in a timely fashion?
What if we had injected it beforehand with a couple of shots of whiskey or some such?
Would we be able to defrost it significantly faster?
It neatly circumvents any issues with food regulations and tax, and I wouldn't really mind if there's a slight whiskey taste to the turkey. It saves on the whiskey sauce after all. ;)

 

[I like Serena]

Our standard for frozen means (home made) is 5mins on 900W, decant onto plate/bowl, stir/spread out, 2mins on 900W.

Interesting. I wonder if that indeed means that my microwave is outdated.
When I use its defrosting mode, I cannot actually set the power. I can only set the type of food and its mass.
Oh wait! Does that mean that you do the same thing I already do? Just hit it with full power, break up the ice, and then hit it some more?
I have 1000 W, which explains that I need 1 minute less.

 

[sophiecentaur]

Is that with the chaos theory solution @sophiecentaur?

Chaos is a trade name, I think. It requires a more advanced power supply ("Inverter") than many ovens use. The pulses are quite short and it's much more complicated than the several seconds of ON-OFF on older ovens.
Chaos comes into its own for large items, I think, in which you can get large regions of ice after a long cook time. That is a health risk sometimes. For small items (single person meals etc) the diffusion time for heating is quite short so it doesn't matter. I still think that local overheating could spoil some items. 1kW could cause a serious hot spot in meat which could toughen it up or dry it out.
I seldom use chaos, preferring to take the frozen item out of the freezer and to let it defrost overnight. A large piece of meat is quite a challenge to defrost ASAP.

 

[I like Serena]

Chaos is a trade name, I think. It requires a more advanced power supply ("Inverter") than many ovens use. The pulses are quite short and it's much more complicated than the several seconds of ON-OFF on older ovens.

The several seconds of ON-OFF is indeed what my defrost mode does, and which I don't consider to be particularly effective, so I never use it.

And yes, I can understand that in theory a chaotically pulsed mode could work, applying power in extreme bursts to break up the ice, such that (close to) full power is still applied.
That is, if microwave manufacturers can get such a system to work while still applying full power.
So now I wonder...

 

[I like Serena]

I've been saying this for years until one day one of our postgrads put one of those stackable aluminium pots (I forget what they are called) in the microwave. He ignored the howls of derision and heated his lunch. We all said it must be because it doesn't have a lid, he put on a lid and repeated the process. No problem. I'd like to hear an explanation for this. I know things like those twisty plastic things with wire in get extremely hot, red even, but large metal objects?

Cheers

As I understand it, one metal is different from another.
It's all about whether the metal responds to an electric field or not.
Copper will definitely respond since it's a conductor, and it will short circuit the microwave.
That's why we have aluminium plates that are suitable for a microwave to heat from the bottom up because aluminium has a low conductance. Low enough not to fry the microwave and high enough to collect heat.
I think aluminium foil will also cause a short circuit, but I'm not exactly sure why. I'd be happy to see more opinions on that.

 

[sophiecentaur]

The several seconds of ON-OFF is indeed what my defrost mode does, and which I don't consider to be particularly effective, so I never use it.

And yes, I can understand that in theory a chaotically pulsed mode could work, applying power in extreme bursts to break up the ice, such that (close to) full power is still applied.
That is, if microwave manufacturers can get such a system to work while still applying full power.
So now I wonder...

Full power would cause local frying of the food after a very short time. A burst of full power (the optimum time would have been found experimentally) can do some melting of ice locally (this will happen in the antinodes of the standing wave pattern). Moving the pattern or the food will allow more average power to be supplied. Moving and pulsing can allow the mean power to be increased without damaging the food. Random is just a refinement, probably. I haven't read of anything more magical about the pulsing system but I suspect that short fast pulses would improve on what the old (relay based?) switching of the magnetron power supply.
Alternatively, the food could be physically whizzed around and about to spread the effect of local heating in antinodes. The cavity would need bearings like a washing machine then.

 

[I like Serena]

I've completed my experiment.
I've diluted my 40% whiskey to about 3% and froze it (stir and shake because otherwise it doesn't freeze at all).
At about 3% it does freeze, and I've hit it with maximum power (1 kW).
Turns out that after 1 minute there is still some ice, but after 1:30 all ice is gone.
My preliminary conclusion: injecting a turkey with whiskey _will_ defrost it in a timely fashion, although some confirmation would still be good.

 

[sophiecentaur]

This surprises me. I have tried keeping Vodka in a freezer and it just separates out, leaving a block of ice and a remain volume of liquid. Perhaps your experiment was not at as low a temperature as mine.
Also, have you ever actually tried to inject a frozen turkey with anything? It's much the same as a block of granite as far as a needle is concerned.

 

[jerromyjon]

Also, have you ever actually tried to inject a frozen turkey with anything?

I think they mean before you freeze it...

 

[sophiecentaur]

I think they mean before you freeze it...

Yep, I know but we already discussed the tax issues of selling liquor along with food, earlier.

 

[I like Serena]

This surprises me. I have tried keeping Vodka in a freezer and it just separates out, leaving a block of ice and a remain volume of liquid. Perhaps your experiment was not at as low a temperature as mine.

Just found this wiki article about freeze distillation.

• Freezing in this scenario begins at a temperature significantly below 0 °C.
• The first material to freeze is not the water, but a dilute solution of alcohol in water.
• The liquid left behind is richer in alcohol, and as a consequence, further freezing would take place at progressively lower temperatures. The frozen material, while always poorer in alcohol than the (increasingly rich) liquid, becomes progressively richer in alcohol.
• ...

So some of it will separate and some of the alcohol will get frozen inside the ice.
And freezing only even starts well below 0 °C as I've observed.

To be honest, I was also wondering why liquor doesn't spontaneously separate through diffusion.
I remember an experiment where we pour water carefully on top of colored alcohol, after which the alcohol spirals through the water to the top.
I'm guessing that in a solution the alcohol is bound to the water molecules through their polar structures.
And that would be exactly why mixing water with another polar substance should help to defrost in a microwave.

Also, have you ever actually tried to inject a frozen turkey with anything? It's much the same as a block of granite as far as a needle is concerned.

Indeed I haven't.
I guess we'll have to buy it at the source if we can.

 

[rumborak]

Here's an idea: given how the lack of liquid water is the problem in the beginning, maybe you could take a thin piece of cloth, soak it in water, and place it on top of the ice. The cloth would get hot very fast, melting the ice below it, thus jump-starting the overall heating process.

 

[sophiecentaur]

Here's an idea: given how the lack of liquid water is the problem in the beginning, maybe you could take a thin piece of cloth, soak it in water, and place it on top of the ice. The cloth would get hot very fast, melting the ice below it, thus jump-starting the overall heating process.

That is only half the problem solved. When you try to thaw out a large piece of frozen food, the first regions of water that have melted will continue to absorb the microwaves preferentially and you risk over cooking those regions whilst the frozen bits are still frozen. The outside would defrost slightly quicker with a 'water jacket' but that doesn't help with the requirement for uniform defrosting throughout.
There is a Health and Safety issue, too. There is a risk that the last few regions to be defrosted will never be taken beyond the safe cooking temperature yet this would go undetected because all the food would 'taste' warm enough. This is why the instructions are always to serve the food "piping hot" - just to be sure.
Patience is required with all food preparation.

 

[I like Serena]

I've repeated my experiment a bit more carefully, and a glass with water and a bit of Vodka defrosts uniformly and pretty quick, while a glass with just water doesn't defrost at all.
Then I thought, let's give that defrosting mode of my microwave another chance.
So I set it to defrost 20 kilograms of bread and applied it to the glass that was still almost fully frozen. It showed that this would take 37 minutes.
Interestingly, within a couple of minutes the ice was defrosted, while the liquid water didn't really get warm.
For reference, my microwave is about 20 years old.

 

[sophiecentaur]

while a glass with just water doesn't defrost at all.

But it's defrosted already !?
"Almost fully frozen" isn't 'deep frozen' (-20°C). You should aim at your experiment mimicking realistic conditions

Interestingly, within a couple of minutes the ice was defrosted, while the liquid water didn't really get warm.

Look up the Latent Heat of fusion of water and compare it with the Specific Heat of water at different temperatures (above and below 0°C) for some interesting thoughts. This link is chatty but has some facts about specific heat.

 

[I like Serena]

But it's defrosted already !?

Yeah, I just skipped over mentioning that both glasses were deep frozen before putting them in the microwave.

"Almost fully frozen" isn't 'deep frozen' (-20°C). You should aim at your experiment mimicking realistic conditions.

Indeed. I only used the defrosting mode as an afterthought. And it takes a bit of time to deep freeze after all.

Anyway. just now I've repeated the experiment with one glass of water with a bit of Vodka (~5% alcohol) and one glass with only water.
First deep freeze, then put in the microwave and use its defrosting mode for 20 kilograms of bread.

Now I see the exact same effect as just using the microwave at full power.
The glass with frozen water/Vodka defrosts uniformly within 1.5 minutes and becomes warm afterwards.
The glass with just ice still did not noticeably defrost after 6 minutes. Afterwards it starts melting from the outside in.
Apparently we first had to wait for some water to form on the outside, which could then heat up.

 

[sophiecentaur]

Yeah, I just skipped over mentioning that both glasses were deep frozen before putting them in the microwave.

Right. I get it. Full marks for your attempt but, unfortunately you have raised another set of questions. Ain't that just the way?
It's hard to make sense of the results, of course, because the amount of actual power that's transferred will depend on how well the Matching is achieved. The "full power" would have been the setting and not the actual amount of RF Power.
It would be interesting if the cavity could be tuned to the individual load but, of course, a domestic oven is One Size Fits All for its tuning and it will also be tuned to avoid too high a standing wave ratio which could damage the Magnetron. I guess a possible improvement could be to have some form of automatic matching but that could be expensive and just another thing to go wrong. They are remarkably reliable devices and I have never (in several decades) never had a failed magnetron. It's silly things like dodgy door catches and turntable motors that have let them down.

 

[Nik_2213]

"The cavity would need bearings like a washing machine then." What about a modest turn-table ? Or the heating pad previously mentioned ??

Our clever oven with the temperature probe has the problem that the probe will NOT go into hard-frozen food. Forward-planning required. Or a 'we deliver' meal...