Sunday, 6 January 2008

The Science Behind Egg Whites in Cocktails

Egg whites in cocktails act as an emulsifier, forging the independent ingredients together. They also change the texture of the cocktail as, when shaken, they produce a foam.

But first, here are the science basics you need to know:
- Egg white is largely protein.
- Proteins are made up of long chains of amino acids, which are similar to beads on a string.

Physically shaking the drink will break these bonds between the amino acids (and the different parts of them), denaturing the protein, and new bonds will be formed. Some amino acids are ‘water loving’ (hydrophilic) and attracted to water, and some are ‘water fearing’ (hydrophobic) and repelled by it. When the bonds are broken, the protein will uncurl, so the ‘water loving’ amino acids are near the water, and the ‘fearing’ are away from it, then new bonds are formed and the egg white has a different texture to the one it had before. Shaking will mix air into the egg whites and the new bonds hold will the air in place, creating a foam.

Without the addition of citrus, this foam would cave quickly. Adding citrus will change the pH of the egg whites. The pH is a measure of hydrogen ion concentration, the lower the pH, the more hydrogen ions. Lemon juice typically has a pH of around about 2.4, and egg whites, 7.7. Lowering the pH (by adding citrus, therefore increasing the hydrogen ion concentration) lowers the reactivity of the protein molecules, preventing a collapse of the foam.

Some time should be put into shaking cocktails containing egg whites, so expect to be shaking it for longer than you would a Cosmo. The longer you shake it for, the more of the structure of the egg whites you break up, and the more air you put into it, therefore the lighter the drink will become.

- Alex

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