Cooking with Copper Chemistry 

    Kids, did you know that whipping eggwhites in a copper bowl gives different results from beating them in a glass, ceramic, or steel bowl? One common technique used in baking is to whisk egg whites in order to make especially light, airy or fluffy delicacies. When air is whisked into egg whites, the mechanical action starts to “unfold” the proteins in the whites. The scientific term for this is to “denature”. The denatured proteins begin to stick together, (or “coagulate”), stiffening the foam and stabilizing the air bubbles. If the foam is overbeaten in a non-copper bowl, eventually the proteins become completely denatured and coagulate into clumps. This is not a good thing. 

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    In turns out that, in copper bowls, the eggwhites react with the metal in the bowl to produce a complex that gives the egg whites a golden color. Some copper ions migrate from the bowl into the egg whites. They become harder to overbeat and give long-lasting “peaks” (a cooking term used to describe shapes that can stand on their own) . Copper bowls produce a yellowish, creamy foam that is harder to overbeat that the foam produced using glass or stainless steel bowls. The copper ions form a yellow complex with one of the proteins in eggs, conalbumin. The conalbumin-copper complex is more stable than the conalbumin alone, so egg whites whipped in a copper bowl are less likely to denature (unfold).

    If a copper bowl is used, then fewer protein molecules are free to denature and coagulate, because some are tied up in conalbumin-copper complexes. In addition to forming complexes with conalbumin, the copper may also react with sulfur-containing groups on other proteins, further stabilizing the egg proteins. Although the iron and zinc found in other metal bowls also form complexes with conalbumin, these complexes don't make the foam more stable. When glass or steel bowls are used, cream of tartar may be added to egg whites to stabilize the whites.

    Try all of these things with an adult partner using several eggs, several different types of bowls, cream of tartar (1/4 tsp for 2-3 eggs), and a mixer. Here is a meringue recipe to check out the different results of your experiments in something edible: 3 egg whites, 6 tablespoons sugar, 1/2 teaspoon vanilla. Beat eggs until frothy. Add sugar gradually and continue beating until stiff peaks form. Add vanilla. Place by the tablespoon onto a cookie sheet and bake at 325° for 15 to 20 minutes. Do your meringue cookies look or taste different based on your cooking variations? Enjoy! 


    Kathleen Carrado Gregar, PhD, Argonne National Labs
    February 2007



    Dr. Anne Marie Helmenstine at