Raw egg whites have long been an integral part of cocktails, responsible for the prized frothy head on drinks like the tart Pisco Sour and the fruity Clover Club. While we’ve previously explained why you shouldn’t be afraid of raw egg whites, understanding why bartenders use egg whites in the first place requires a bit of chemistry. (Don’t worry if you snoozed through high school science. It’s all easy-to-understand metaphors from here on out.) We talked to our favorite egg scientist, Dr. Deana R. Jones, research food technologist with the Egg Safety and Quality Research Unit at the USDA Agricultural Research Service, to get a look inside the shaker tin at the science of egg whites in cocktails.
Why Egg Whites Go From Clear to White
There’s a lot more than mixing going on in the shaker when you add egg white to the mix. The texture and volume of the mixture are changing, and it’s all thanks to the proteins inside the egg white. “Even though albumen [aka egg white] is a clear, viscous fluid, it’s actually made up of a whole lot of proteins,” Jones explains. “The whole reason it’s clear is that the [proteins] are tightly wound—they’re bound on top of each other.” But smacking them around in the shaker causes them to unwind and reconfigure. “The reason the albumen turns from a clear fluid into a white substance—whether it be when you’re cooking it, or when you’re beating it and it becomes a fluffy white foam—is because the proteins begin to unwind and stretch,” Jones says, comparing shaking to waking up the proteins in the morning, causing them to yawn and stretch out. “As they start stretching, they start holding onto each other’s hands, in a way. They start forming a network, and that’s when it starts to turn white.”
Why Egg Whites Get Fluffy
“We’re talking about aeration,” Jones says, pointing out that the same chemical change happens when you whip egg whites with a whisk. “As the proteins unfold and hold each other, they’re hugging an air bubble. They’ve made this air bubble that they’re all wrapping their arms around. As long as they keep holding hands, they’ll keep that air bubble stable.”
When you have enough proteins making rings around air bubbles, the proteins form a network, changing the composition of the liquid and increasing the volume, which is why you’ll see that sizeable foamy head on top of a drink. While the exact amount of expansion varies based on a lot of factors, Jones says, “in a perfect scenario, it can easily grow over 10 times in volume.”
Why Sometimes Your Egg White Foam Flops
Jones references a classic cooking mistake to illustrate one of the factors that can undermine perfect foam: “Someone is trying to make meringue and it just goes womp womp womp. A lot of times that happens because you keep whipping and keep whipping, and the proteins are stretching to [keep their bonds]. They’re on their fingertips, and then they just can’t do it anymore, and they let go. The foam collapses, or in my world, they say the foam ‘has broken.’ When that happens, you can’t repair it. You broke their fingers and they can’t hold hands anymore.”
Why You Should Perfect Your Egg White Separation Technique
“If you are separating the yolk and the albumen from an egg, and you accidentally nick the yolk, some of the yolk material enters the albumen, letting in all the nutrient-rich fats from the yolk,” Jones says. “That is like putting mittens on the hands of the proteins, preventing them from holding hands and preventing a foam from forming. That’s why you have to be careful when you’re separating the yolk from the albumen.” Jones reminds home bartenders to separate eggs into a separate container before adding them to the rest of the ingredients, just in case your expert egg separating skills do happen to fail you.
Why You Should Always Dry Shake Egg Whites
“If someone puts albumen in a cocktail [tin] with ice, it’s going to delay the whipping,” Jones explains. “It’s going to take longer because those proteins are not going to readily unfold and make a foam if they’re really cold. You’ll have to shake longer and longer.” Always remember to dry shake your egg whites with the liquid ingredients first, before adding ice in a second round of shaking.
Why Egg White Substitutes Will Never Live Up to the Real Deal
Some bartenders substitute yogurt or aquafaba (chickpea water) for egg whites to create a vegan cocktail with a similar texture to a classic egg-frothed drink. “Those are both protein-rich foods so the proteins still do the heavy lifting,” Jones explains, but the resulting drink won’t quite match the cocktail with which drinkers are familiar. “Yogurt, legumes and beans have lipids associated with their protein matrices, while an albumen does not. The albumen is virtually fat-free, so it’s more of a pure protein. When you’re getting foam from a legume or bean source, you’ll still get foam but it’ll just be a different type of foam. People are going to notice a slightly different texture and mouthfeel.”