Why is a copper bowl recommended for whipping cream and egg whites? They say you can get the whipped cream or egg whites "higher" or "stiffer" if you use a copper bowl.  Why is that?
According to wikipedia, the copper bonds to the sulfur in the egg whites, which has the effect of stabilizing the foam.

http://en.wikipedia.org/wiki/Egg_white#Copper_bowl

Cookwise by Shirley Corriher says the same thing.