Reactive Pan - is one made from a material that reacts chemically with other foods. Aluminum and copper, metals that conduct heat extremely well, are the 2 most common reactive materials used to make in cookware.
Lightweight aluminum, second only to copper in conducting heat, reacts with acidic foods, imparting a metallic taste, and can discolor light-colored soups and sauces, especially if you stir them with a metal spoon or whisk (it is a very soft metal). For that reason, you should neither cook nor store light-colored foods in aluminum cookware. Anodized aluminum has a hard, corrosion-resistant surface that helps prevent discoloration.
Most copper pots and pans are lined with tin to prevent reaction. However, tin is a very soft metal, so it scratches easily and then exposes foods to the copper underneath.
Non-Reactive Pan: When a recipe calls for a non-reactive cookware, use clay, copper, enamel, glass, plastic, or stainless steel. Stainless steel is the most common non-reactive cookware available. Since it does not conduct or retain heat well, it frequently has aluminum or copper bonded to the bottom or a core of aluminum between layers of stainless steel. Although expensive, this kind of cookware offers the benefits of a durable, non-reactive surface and rapid, uniform heat conductivity.
Glass cookware is non-reactive and although it retains heat well it conducts it poorly. Enamelware is non-reactive as long as the enamel is not scratched or chipped. Cast-iron is considered reactive; however, we have to say that our extremely well-seasoned pans seem to do fine with tomato sauce and other acidic foods as long as they do not stay in contact with one another for extended periods.