Stainless steel, tin lined copper, non-anodized aluminum, clay, enamel, glass, or plastic are all non-reactive.
A reactive pan is one made from a material that reacts chemically with other foods, such as aluminum, copper and cast iron. The materials react with acidic foods, imparting a metallic taste and will sometimes discolor light colored soups and sauces a light green or gray! Anodized aluminum has a hard, corrosion-resistant surface that helps prevent discoloration, so it is ok to use. Also, avoid stirring light-colored sauces and soups with an non-anodized aluminum metal spoon or whisk.