Pour enough water in the aluminum pan to completely cover the black portions. Add 1 teaspoon vinegar for every cup of water you use.
Boil the solution for 20 minutes and remove it from heat.
Scrape the pan with a wooden spoon to loosen the black stain. Rinse the pan with cold water. If black stains remain, you need to use baking soda.
Cover the stained portions with baking soda and scrub with a nylon scrubber. Rinse the pan with cold water and repeat until the pan is completely clean.