Does Microwave Energy Transfer Depend on Contents Inside?

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Sometimes a jar of peanut butter, kept in the refrigerator, will be too hard to spread. The 'cure' of course is to heat it - in the microwave.

This often works well -- unless the is a scrap of that heat-bonded foil seal left on the edge of the jar. The jar rim is about 2mm (0.08in.) thick.

If it is just a speck of foil, it generates a minor plasma explosion and all is well.

Around 12mm (0.5in) long, there is a continuous plasma discharge as the edge of the plastic jar decomposes (Polyethylene Terephthalate), leaving behind the Carbon, which of course is conductive. Conductive enough to sustain continued burning of the plastic!

The audible indications are an initial 'Pop' followed by a loud 'Hum' as the power transformer in the oven is overloaded by the short circuit in the plasma cloud.

I have never let the process go to completion as I don't want to replace the oven, it also takes some effort to remove even 1 seconds worth of the burned plastic stench from the oven interior.

Now I usually remember to check for left-behind foil before inserting in microwave!

Cheers,
Tom

p.s. IIRC, the heating effect for non-conductive materials is proportional to their di-electric constant. Water, falling around 78-80, is usually what heats the most.
 
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^^^ Yep. That's one of the reasons I stopped buying TJs peanut butter and started filling up an empty jar at the bulk bin of the local co-op. It was frustratingly difficult sometimes to remove that plasma inducing metallic residue from the rim. I used to scrape it half-effectively with a butter knife and then end up with tiny bits of foil in the peanut butter.

The other reason is that the bulk peanut butter from the co-op tastes a *lot* better than the stuff TJs sells.
 
JT Smith said:
the bulk peanut butter from the co-op tastes a *lot* better than the stuff TJs sells.
Thats thanks to the ... anonymous supplements .... dust, grime, bugs, hand juice ... :oldruck:
 
Why would Trader Joes peanut butter have all that stuff in it? :-)

Seriously, the bulk stuff is clearly a higher quality product. It doesn't even have salt in it which I was certain I had to have in my peanut butter in order to like it. I was quite surprised when I learned after buying and eating it that didn't have any. I guess I don't need salt in my peanut butter after all -- at least if it's good peanut butter.

I could go around the corner to shelves in the store and buy the exact same product from the same producer already in a jar for only slightly more money. I know I'm not saving the world by reusing a jar. I just like making a big sticky mess in the store.