Here’s some science for you: A non-reactive bowl is a bowl made of a substance that won’t react chemically with the foods that are placed in it. Reactive bowls are often made of metal, like copper, cast iron, or aluminum, or plastics that stain easily.
When a cook adds any high acid foods to these bowls — like lemon juice, most citrus fruits, or tomato sauce — they may actually react with the metal in the bowls and impart a metallic taste to the foods. If a cook needs a metal bowl that will not react, he or she will always want to look for stainless steel, since it tends to resist reaction with high acid foods.
Under some circumstances, a non-reactive bowl will not serve you as well as a reactive bowl — for instance, many chefs prefer to use copper bowls to whip egg whites. The egg whites react with copper and not only whip faster but are also more firm and stable. Note that if a copper bowl is advertised as non-reactive, it usually has a stainless steel or other coating that will prevent this reaction.
In general, cooks can use any type of bowl to make most cakes and cookies. The time that the ingredients spend in the bowl is generally so short that they won’t have time to react with metals. Glass, ceramic, stainless steel, or any non-reactive plastic bowl is still a better choice, however, especially if the ingredients will sit for any length of time. Cooks should always choose a non-reactive bowl for high acid ingredients, and never mix something like a vinaigrette in an aluminum bowl.