How important is it for liquids to rotate in the microwave?

[Annie-Xmas]

Someone just brought me a Very Big Cup of Cappuccino Goodness that needs to be warmed up. I can fit it into the microwave, but it’s a very tight squeeze. No way in hell it is going to rotate.

I know it’s important to have solids rotate so the microwaves hit every bit, but how about a cup of liquid? I don’t feel like puttng it into two smaller cups.

[KlondikeGeoff]

For a few years, we had a microwave oven that did not have a rotating plate. For solids, we often stopped it once and twice and rotated the dish by hand.

For liquids, we never did that and they always heated up just fine.

[New_Beginning]

I don’t see how it’d be important for a liquid, as you can just do a complete mixing of it to even things out in 2 seconds after it’s done heating.

The only thing I could see being a problem is that it might have a greater tendancy to “superheat” the liquid, in which case be careful taking it out of the microwave or you may end up with some surprise boiling water on your fingers.

(Hijack)What I’m far more confused about is why microwaving instructions on the packaging of some microwavable food tell you to rotate the food manually half-way through, even if you have a working turntable.(/Hijack)

[Baracus]

The issue with rotating solid foods is to ensure even heating. With a liquid a quick stir will even out any “hot spots” in seconds. More than likely convection will have eliminated any hot spots anyways.

[Q.E.D]

@New_Beginning

The only thing I could see being a problem is that it might have a greater tendancy to “superheat” the liquid, in which case be careful taking it out of the microwave or you may end up with some surprise boiling water on your fingers.

Not going to happen with cappucino. Pure water can superheat because of the lack of nucleation sites for boiling to start, but since cappucino has lots of dissolved goodies in it there are plenty of nucleation sites.

[HorseloverFat]

Id be more concerned about having the microwave plate spin underneath it and potentially causing a spill inside the microwave.

[minor7flat5]

As others have said, probably no big deal because of natural convection.

Here’s some interesting info on those hotspots…

Hammack, William. “The Greatest Discovery Since Fire.”
Invention & Technology Spring 2005: 51-52.

…Spencer said in his 1945 patent application that radiation heating works best when the wavelength is comparable to the size of the food being cooked. But that meant the wavelength was also comparable to the size of the oven cavity, which in turn meant the microwaves could easily set up a standing wave inside it, causing uneven heating. As one engineer said, “If you put a hot dog in that, it would be cooked in the middle and raw on the ends.” Putting the food on a rotating turntable could reduce this problem but not eliminate it.

To reduce the problem of uneven heating, he needed to continually modulate the standing waves within the oven, a trick that in technical parlance was called “mixing the modes.” The most promising solution was to vary the size of the oven cavity while the food was being heated. First he tried using a small motor to move one wall of the oven back and forth, but this proved to be too complex and expensive for mass manufacturing, partly because of the motor and partly because radiation leaked out of the joint between the moving wall and the body of the oven. So Bock implemented a solution developed by another engineer: Instead of changing the actual size of the cavity, he changed it in a virtual way.

From the upper wall of the oven he hung rotating rods. A motor turned them at about two to three revolutions per second. As the radiation bounced from top to bottom of the oven, this “mode stirrer” alternately blocked and let pass certain parts of the waves, creating a constantly shifting set of standing waves. While the solution was not perfect —even today no microwave oven warms food completely evenly—it distributed the microwave energy through the cavity well enough.

[panache45]

The liquid itself shouldn’t be a problem, but might there be a problem with the “Very Big Cup” heating unevenly, or would it be getting enough heat from the liquid?

[dracoi]

@New_Beginning

(Hijack)What I’m far more confused about is why microwaving instructions on the packaging of some microwavable food tell you to rotate the food manually half-way through, even if you have a working turntable.(/Hijack)

My microwave heats the bottom of most solid foods faster than the top (especially noticeable in defrost mode). The turntable can spin it around, but can’t flip it over.

The more likely reason is that instruction on foods have to be idiot-proof*. They can’t assume you have common sense, let alone a turntable.

• I like how they put “Warning: Hot steam” on a package of microwave popcorn or “Caution: soup may be hot” on ramen cups. It damn well better be hot!

[Bluffcityguy]

@dracoi

• I like how they put “Warning: Hot steam” on a package of microwave popcorn or “Caution: soup may be hot” on ramen cups.

Or my favorite (and subject of one of Unca Cecil’s columns): “Remove shell before consuming nutmeats”

Why does the peanut bag say, "Remove shell before consuming nutmeats"?

**ETA:**To mitigate that further threadjack I’ve just committed I’d go along with you on the “idiot proof” assumption: last I looked, not all microwaves have turntables, especially the lower end (i.e., cheaper) models. I’ve never worried much about flipping over the food I’m microwaving though, unless the instructions on the package tell me to do so (the manufacturer knows best, at least until I learn otherwise…).

Cheers,

bcg

[New_Beginning]

@dracoi

My microwave heats the bottom of most solid foods faster than the top (especially noticeable in defrost mode). The turntable can spin it around, but can’t flip it over.

The more likely reason is that instruction on foods have to be idiot-proof*. They can’t assume you have common sense, let alone a turntable.

But there are some instructions that specifically mention rotating the food, and explicitly say to do so even if you have a turntable. I’ll have to find an example, but I’ve seen it many times.

[Bluffcityguy]

@New_Beginning

But there are some instructions that specifically mention rotating the food, and explicitly say to do so even if you have a turntable. I’ll have to find an example, but I’ve seen it many times.

I will have to look more carefully. In a couple decades of using a microwave I’ve never seen microwave cooking instructions which have mentioned a turntable. At all. Much less explicitly state “rotate even if using a turntable”.

Cheers,

bcg