The idea occurred to my daughter Lindsay and me when she was making a birthday cake for my wife. Why do cooks whip egg whites in copper pots? My first stop was a query to Darcy O’Neil, of Art of Drink fame, drink chemistry guru and author of the definitive book on soda fountains titled Fix the Pumps. His answers combined with a little digging in the literature surfaced the chemistry behind it. There are basically two factors at work here, one physical, and one chemical. The physical whisking folds air into the albumen creating the foam. But it also unravels some of the amino acid molecules “opening them up” to combine with the air and water. When you whip in copper, the physical contact with the whisk frees up some copper ions that combine with the sulphur in eggs to make those unraveled amino acid bonds with water and air much more stable…yielding a more stable foam.
So the next question was, how come we don’t use copper lined shakers in bars that make drinks with egg whites as an ingredient like the Pisco Sour, Ramos Gin Fizz et al.?
Darcy didn’t have an answer to that one, nor a source for copper-lined shakers, though he did suggest testing the theory with copper ball bearings, the thought being ice may not be hard enough in a shaker to release the copper ions. (and a suggestion to use a solid metal shaker rather than a Boston Shaker!)
Two other alternative methods that improve foam stability are to add an acid (citric acid from the limes in the recipe may already be maximizing the foam),and cream of tartar which also lowers the pH.
So we’re going to do some experimenting and determine whether or not we can use this copper/egg white interaction to make a better Pisco Sour. Not having access to copper ball bearings, I’m thinking I’ll stop by the hardware store for some copper plumbing fittings and a micrometer and stop watch to measure foam height and stablility.
Stay tuned…more to come.