What happens to the cream and egg white in a Ramos Gin Fizz?

Question

A Ramos Gin Fizz uses both egg white and heavy cream in order to form an extraordinarily stable and dense head on the drink.

When egg white is whipped, it forms a foam through protein networking. When cream is whipped, it forms a foam because fats capture air in bubbles. This question tells us that whipping them together doesn't work because the mechanisms interfere.

Furthermore, we're working in an acidic, alcoholic environment. This ATK article explains that cream thickens instead of curdling because the fats (again) interfere with the protein networking action, this time of the caseins.

I've gotten good results on the foam even when I omit egg white, meaning that it's probably not an integral part of whatever chemistry is causing the foam. I've also noticed that I get better results if I mix the club soda and cocktail streams as I pour them, making me think there's something of an emulsion happening during the pour, and the gas in the foam starts as mostly CO2.

The Cocktail Codex by Death and Co. contains a recipe for the RGF made in an iSi whipper, so whatever's happening, it works just as well with CO2 as it does with N2O.

What's causing the foam to be so stable?

Answer 1

Foams are a little complicated, and while it's true that an egg white foam will lose stability with fats, it's also true that fats can create foams, and fats and proteins can also combine to create a stable foam. In the baking world, we create meringue with egg whites and pâte a bombe with egg yolks, but we also create foams from whole eggs (such as in a biscuit Joconde).

Other ingredients can stabilize the foams for varying reasons. Sugar increases the viscosity of the continuous phase of the colloid which helps stabilize the foam. Mixing alcohol and water together increases the viscosity over either liquid by itself. Alcohol also denatures proteins, which can help create a foam. Acids both help create a foam and also prevent the proteins from bonding as tightly which helps prevent syneresis in the protein matrix (pushing out water).

Eggs are complicated mixtures of water, proteins, fats, phospholipids, sugars, and other molecules that all contribute to the stabilization of emulsions, foams, and other colloids.