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The Science of the World’s Greatest Sauce: Mayonnaise

And how to make your own.
By and

Published July 7, 2023.

Store-bought mayo is amazing, and you should never let anyone shame you for using it. But homemade is also incredibly special, customizable, and easy. It all starts with a little sweet emulsion science. 

What Is an Emulsion?

Mayonnaise (like cream, butter, and ice cream) is an emulsion. We take liquid oil—which is thin, slick, greasy—and turn it semisolid and creamy. 

If you were to zoom in on a dense emulsion such as mayo, you would see tons of tiny oil droplets tightly packed together—but not actually touching. Keeping those droplets separate is the key to a stable emulsion. But it’s a fragile business because the droplets are attracted to one another, and if they merge, the emulsion fails. 

That’s why emulsions contain emulsifiers (in mayonnaise, these are the lecithin in egg yolks and the polysaccharides in mustard), which form thin barriers around each oil droplet so that they can coexist without coalescing into greasy pools.

As you crowd more oil droplets into the small amount of water in a mayonnaise, it becomes thicker because it makes it increasingly hard for the liquid surrounding the droplets to flow. 

Our Senior Science Research Editor Paul Adams came up with a helpful analogy. Think of the water in mayonnaise as a group of bikers, like in the Tour de France. As a group, they move and flow rapidly. Think of the oil droplets as elephants. If we add just a few elephants amongst the group of bikers, the bikers are going to slow down as the animals get in their way. But they can keep moving. But let’s say we add a lot more elephants. At some point they disrupt the flow of bikers so much that they can no longer keep moving. That elephant-loaded bike race is mayonnaise.

The key to making a stable mayonnaise is to break the oil into tiny droplets and have emulsifiers in place that will surround those droplets. 

The lecithin in egg yolks is a compound with one end that is attracted to fat and one end that is attached to water. The fat-loving ends of lecithin molecules line up on the exterior of oil droplets while their little tails jet out into the water. They are ready and waiting to do their job—you just need to serve them up tiny oil droplets. 

How to Make Homemade Mayonnaise

I first learned how to make mayo using a whisk. If I’m somewhere without access to any heavy machinery, I’ll still do that. The challenges of making mayo by hand are twofold: You must pour the oil in slowly with one hand while whisking vigorously with the other so that the oil gets broken into properly small droplets. Mess up either one of those and you have a break on your hands. It’s doable but challenging. 

Bringing in power equipment can make this process a lot easier and generally more failproof. In Senior Editor Lan Lam’s recipe for homemade mayo (which, by the way, uses pasteurized egg yolks, for those who don’t want to eat raw eggs), she uses a food processor. Here’s how it works.


1. Stir 3 tablespoons of water, 2 egg yolks, and 4 teaspoons lemon juice in bowl until no streaks of yolk remain. 

2. Microwave the mixture until it hits 160 to 165 degrees, stirring every 10 seconds (this makes the yolks fully safe to eat).

3. Add ¼ cup oil, ¾ teaspoon table salt, ½ teaspoon mustard, and ¼ teaspoon sugar; whisk to combine. 

4. Strain mixture through fine-mesh strainer into bowl of food processor. With processor running, slowly drizzle in remaining 1¼ cups oil in thin stream over the course of 2 minutes. 

Want to learn more about mayonnaise? Check out the full episode of What’s Eating Dan? below.


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