Monday, March 9, 2015

Cooking With Dr. Science

Joe over at North Central Idaho published something he noticed while preparing stuffing in his oven, namely that the aluminum foil he covered the stainless steel dish with had developed "burn through" holes in it. Not wanting to include aluminum in his stuffing, he gave up the practice.

For myself, the term "galvanic corrosion" rings a familiar bell as in when you place 2 metals with different galvanic ratings into a conductive liquid the anode tries to dissolve and transfer itself to the cathode. In this case the aluminum dissolves first which protects the steel from corrosion in salt water. Ask the Navy, they're familiar with this.

The stuffing pan, being a big battery, had a steel cathode, an Aluminum anode, and a lot of steam. Pure water is a poor conductor so the electrolytes, salt for example would migrate from the stuffing to the aluminum wherever the two came in contact and reduced the foil to aluminum oxide. A friend of mine set up an experiment:
I put the salt water in a stainless steel dish and put aluminum foil over the top, then pushed down the foil in the middle so that it contacted the water.  I checked it in about two hours and there were lots of little holes in the foil where it was in contact with the water.  I put another piece of foil over the dish and made sure it did not contact the water and left it while I went to work.  When I got home, about five and a half hours later, there was no corrosion of the foil.  Not surprising, that, but it was an easy check.

I didn't think to set up the cell to measure the voltage and it wouldn't have mattered if I had because I don't have a voltmeter capable of measuring that level with any accuracy.  A Wheatstone bridge would be the best way.

I didn't get any of the dark tarnish that the photo with the blog shows.  I suspect the onions, and maybe the next time I'm cooking with onion I'll see if I can turn some foil black.

Looks to me like using aluminum foil and stainless steel dishes might work okay if the foil doesn't touch the food, which might explain the observation that the effect isn't seen with foods other than stuffing.
It would also probably work if you used a glass container.

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