The box around my roll of aluminium foils states,
“covering stainless steel dishes with aluminium foil is not advisable”.
Why? Time for some research. Professor Google to the rescue once again.
I found some very complicated information at the Anodizing World blog, and have boiled it down (boom! tish! kitchen pun) to the following basics:
- Aluminium foil is not pure aluminium, but instead has a fine layer of aluminium oxide on its surface;
- In the presence of water, a chemical reaction occurs between the aluminium oxide and the stainless steel (which itself is a combination of several elements, including chromium);
- The reaction, which involves movement of elections, results in degradation of the aluminium; and
- Discolouration or even holes may form in the layer of foil.
There you have it. Science in the kitchen, and not just in the chemical reactions of cooking.
[image thanks to top quark22 on flickr]