Mysterious Microwave Oven

[gumboil]

I recently disposed of my Panasonic microwave oven that we'd had for oven fifteen years as something shorted inside it following the routine changing of the bulb that illuminates the cavity. The microwave concerned was rated at 850W or Group E in power.

Following the demise of the microwave, we bought another Panasonic model rated at 1000W microwave power, but still within the highest group, Group E.

Now to the mystery. In the old microwave oven, two cups of milk poured into a plastic jug took 4 minutes and 20 seconds to boil. When the milk boiled, it was necessary to be pretty quick to switch the oven off or the milk would boil over in seconds.

In the new microwave oven, the same volume of milk takes just over three minutes to start boiling, which is fair enough given its increased power. However, the milk rises much more slowly in the jug and takes about thirty seconds to reach the top of the jug. In addition, many people have commented that the milk temperature is not as hot as it was in the previous oven after "boiling". In support of this is the fact that a "skin" does not form on the milk, which I understand only happens when milk is truly boiled.

I can't for the life of me understand what is going on here. As I see it, the milk must boil for it to rise to the top of the jug i.e it's doing the same as it did in the old microwave oven, except it's rising more slowly. So if it has boiled, why is it not as hot as the milk from the old oven?

The cavity size is identical in both ovens at 27 litres and the only difference between the two was that the old cavity was painted cream by the manufacturer and the new one is stainless steel. Both ovens have a working glass rotating plate of identical diameter on the floor of the cavity.

All comments greatly appreciated.

[Cmitchell]

Hello Gumboil

I'd like to hazard a guess that your new microwave oven has a (more efficient) fan. I'd say when the milk is boiling, it's boiling,whether it is rising up the sideof the jug quickly or slowly. But the bubbles on the surface are more likely to "break" if there is a more efficient fan, or a fan providing "fresh" air as opposed to warm recirculated air. Therefore is the bubbles are being broken more easily & quicly in new icro then that will be why bubble level is increasing at a slower rate.

But I am truly baffled about the skin business.

Hope this helps and if not then it poses food for thought.

Mitchell

[gumboil]

Thanks Mitchell. You may well be right about the fan as I've noticed that the new oven fan stays on even after the set time period has elapsed, sometimes by up to a couple of minutes. It's as if the fan is making sure that all the "heat" has gone out of the oven.

I wondered if the more efficient cooling of the fan was lowering the temperature of the milk, but if I remember my school physics properly, a fan does not lower the temperature of a room, microwave cavity or any other object and only servers to move cooler air through it more rapidly. Apparently, no temperature drop is discernible in any room being cooled by a fan. If this is the case, the fan can't be cooling the milk. Besides, I remove the jug immediately the milk boils.

Please keep providing your suggestions my friends.

Thanks

[markja]

the old micro w may have heated all the milk at once, therefore all the milk would produce bubbles. the new one may only heat a band of milk and thermal movement mixes it. in this case the 'band of milk' would produce bubbles but not the milk being heated by thermal motion.
does this make sense any one? or am i talking cr4p?
i don't think the fan would have more than a verrrrry small effect on cooling of the milk.

[markja]

i've just thought of how to show what i mean.
the difference is like heating a pan on the hob, it all heats at the same time and boils at the same time.
but if you stick a red hot poker in, the area around it boils and the rest takes longer to heat up.

[gumboil]

Thanks markja. It's certainly an interesting idea and I don't think you're talking cr@p at all!

I'm seriously thinking of writing to Panasonic about this to see if there's an "official" explanation for this phenomenon as it's bugging me because it seems so illogical.

Thanks again..