Never heat acidic foods with aluminum. You can see in the color of the foil that the aluminum has become integrated with the food after cooking, and aluminum ions can survive in your body for about 2 years. They replace calcium and other metals in metalloenzymes responsible for metabolism and immune system function.
Additionally, despite the aluminum industry's propaganda, there is a direct link between aluminum in the diet and Alzheimer's disease. For non-acidic foods, aluminum works better at or below the boiling point of water. You can bake potatoes or other root vegetables wrapped in aluminum, but it's best to insulate them with a layer of parchment paper.
