Serious chefs have preferred copper mixing bowls for centuries. They are beautiful, of course, but their true beauty is in their superior function. No other container gives you the lush, stable peaks of meringue you can whip up in a copper bowl. Copper is equally handy when mashing potatoes to a fine froth or spinning heavy cream into whipped cream. But its classic bonafides come from copper's reaction with raw eggs -- basic chemistry with a culinary bonus.
Meringue Chemistry 101
When you whisk egg whites in a copper bowl, some of the copper ions detach from the bowl and bond with a protein in the egg whites called conalbumin. This forms a strong, stable conalbumin-copper complex that delays any tendency in the expanding egg foam to deflate. Whisking mixes air with the egg, creating bubbles that expand the volume of the liquid up to eight times, as the egg protein uncoils and stretches. The more the protein stretches, the stiffer the beaten egg foam -- up to a point.
If you've ever beaten egg whites past their stiff point, you've experienced them falling apart. That's what happens when the protein bonds overstretch and break -- and you can't fix it. What copper does is strengthen the protein so it is tougher and holds the moisture in the air bubbles more efficiently. The conalbumin-copper-strengthened egg white beats to a hard peak that won't dry out and collapse.
Treasure Your Tools
Copper bowls are expensive. Real copper represents an investment that will last for generations with the right care -- and there's not much point in investing in first-rate kitchen tools if you don't make them last. Hand-wash your bowl with mild soap and water after using it and dry the bowl before putting it away. Air-dried copper is prone to discoloration that requires energetic polishing -- the bowl is supposed to make your job easier, not harder, so skip the tarnish.
Copper is reactive -- the reason it reacts so well with egg whites -- so never use copper cleaner on the inside of the bowl. Cleaners can destroy the reactive surface. If you have to polish the exterior, mix up a natural paste of white vinegar and flour or baking soda and lemon juice, to bring back the shine. Display the gleaming copper to enhance your kitchen decor by hanging it where it catches the light. Just keep it away from steam or moisture to prevent extra maintenance.