Eggs – Reasons for separating eggs in ice cream

eggsice-cream

There are a lot of recipes requiring the eggs in the ingredients to be separated. And I know that whipping whole eggs cannot foam up as much as just whipping egg whites.

But why separate eggs in making of the custard for ice cream? Egg whites can foam up better than egg yolks, so it seems counter-intuitive to remove egg whites from the recipe because you would want to incorporate more air into the ice cream, right? :/ I can simply use 1 whole egg for every 2 egg yolks required in the recipe.

I don't think I need to taste egg in ice cream. Can I assume the reason to add egg is just for the color?

Referring to the Wikipedia articles: Yolk, egg yolk is nearly 1/4 fat and 1/3 protein; Egg as food, whole egg is nearly 10% fat and 10% protein. If we ignore the protein and through some clever maths, can I adjust the amount of cream and use whole eggs without separating eggs?

P.S. I'm sorry for being a sciency person and not just follow recipes but I am curious.

Best Answer

Milk and cream are essentially made up of water, fat, and protein molecules. Within milk and cream, the fat globules are already emulsified in the surrounding water by casein (one of the proteins found in milk and cream). This means that casein molecules surround each fat globule and prevent them from coming together. This is why milk doesn't separate into fat and water, even though it's made up of two substances that don't naturally mix.

However, casein is a little too good at emulsifying the fat. When we add egg yolks, the lecithin in the yolk displaces some of the casein surrounding each fat globule. This partially destabilizes the emulsion of the milkfat by casein and allows some of the fat globules to partially coalesce when the ice cream base is chilled and aged overnight.

Destabilization of emulsion

Partially coalesced fat forms a network that traps and stabilizes the air that is incorporated into ice cream while churning, leading to slower melting, better shape retention, and overall improved texture. Lecithin is why we need egg yolks.

Egg whites, however, are mostly water and don't contain lecithin. Adding water to your ice cream base leads to an unfavorable icy texture in the final product and doesn't contribute to partial coalescence of fat. Water is why egg whites are typically left out.

Further reading:

  1. Chart demonstrating fat interactions with and without an emulsifier

  2. More on factors affecting partial coalescence in ice cream

  3. In-depth overview of ice-cream emulsifiers

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