making mayo with stick blender

How Mayonnaise Works – Jamming Fat Droplets in Water

Still think the only way to make mayonnaise at home is by taking a whisk and some hard work for a couple of minutes? Luckily, times have changed and you can now make mayonnaise in a matter of minutes, using an immersion blender.

Mayonnaise does remain a tricky product. Mix the oil in too quickly and it might split. It’s a balancing act to get in all of that fat (over 70% of mayo is fat!). We’ve got some tips and tricks and scientific understanding to help you make great mayonnaise!

Mayonnaise contains a lot of tiny oil droplets

Despite the fact that mayonnaise can be tricky to make, especially using home-style equipment, it is at its core quite simple: oil droplets crammed together in a little bit of water.

simplified micro view of mayonnaise
Simplified microscopic view of mayonnaise: a lot of tiny fat droplets are dispersed in water.

These dispersed oil droplets in water are what scientists would call an emulsion. Two liquids that don’t mix have been put together. Even though the fat droplets might want to split from the water, they can’t. There are so many fat droplets in that little bit of water that they’re literally barricading the way out for each other. They can’t move. They’re stuck.

Mayonnaise needs a lot of fat

In order to closely pack all these tiny oil droplets, you need a lot of fat. It’s why mayonnaises contain (well) over 70% fat. If there’s less fat, it’s very prone to splitting since the particles won’t be jammed together sufficiently.

Aside from the fat, the main ingredient is water, which makes up (way) less than 30% of the mayonnaise. Nevertheless, you’re able to fit all of that fat into a little amount of water. How does that work. Have a look at the illustration above again. Notice how most of that illustration is yellow, representing fat droplets. Only a small amount of that drawing is white, thus water. The oil droplets fill up most of the space and you only need a little bit of water to surround these droplets.

Small droplets make the mayo white

Mayonnaise is generally (off)white in color. However, both the oil and the egg are either translucent or yellow. Something clearly changes when you mix the two. Again, it’s because of all those tiny oil droplets. These tiny droplets reflect light in a lot of different directions, making mayo white. It’s the same reason that milk is white, milk also contains small structures within the milk that scatter light around.

Low-fat mayo requires extra stabilizers

It is possible to make mayonnaise with a low(er) fat content. However, you will need to add additional stabilizers to keep those oil droplets in place. You’ll often find starches being used to do so, or a large bulky molecule such as carrageenan.

Main ingredients of mayo: egg + oil

To make this stable emulsion, traditionally two key ingredients are used: egg and oil.

Eggs are made up of mostly water. As such, it provides the continuous water phase that the mayonnaise needs.

The second ingredient is oil. You can theoretically use a wide variety of oils. However, some oils might give the mayo an undesirable taste. It’s why neutral tasting oils such as sunflower oil or canola oil are commonly used.

An oil is a type of fat, a so called triglyceride. An oil is liquid at room temperature, whereas a fat (e.g. butter fat) isn’t. For making mayonnaise you need an oil since you need the fat to be liquid while pouring it into the water.

Making mayonnaise can be tricky

Once you’ve made mayonnaise it’s a very stable product. It will no longer split spontaneously. However, getting there can be tricky. It is very important that you have the time to break up the oil into tiny droplets to mix them into the water.

There are three main ways to do so:

  1. Slowly add the oil. This gives you time to break up the fat into droplets. If you’re making mayonnaise by hand, using a hand held whisk, that’s what you’ll need to do. While whisking vigorously, you slowly pour in some oil, breaking up the oil into droplets.
    • Major disadvantage: it’s slow, and still prone to split
  2. Use a lot of force. In factories nowadays, very strong mixers, called high shear mixers are used to mix the water and oil. By balancing these just right, the mixers can break the oil into tiny oil droplets.
  3. Both. At home, you’ll likely want to use a mix of these two. You could use a strong blender for instance, and slowly drip in the oil. Our favorite method though is using an immersion blender.
making mayo with stick blender
The easiest at-home method in action.

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Use an immersion blender

In the video above, we use an immersion blender to make mayonnaise. It’s a very simple, pretty (though not completely) fool-proof method. You simply add all ingredients for the mayonnaise in a jar. Using a stick blender, you then gradually mix the two phases together. So why does it work? Why can you add all ingredients up front?

When you’re using an immersion blender you’re initially just mixing the bottom part which contains the water. Oil has a lower density than water so will sit on the top. The vortices created by the blender pull the oil down, but not so fast, nor so vigorously, that everything splashes around. Instead, the water remains at the bottom, while the oil is slowly pulled into it. Its strength ensures that the oil breaks up into droplets, dispersing them through the water.

homemade mayo
Thick gloopy mayonnaise

Emulsifiers make mayo possible

So far, we’ve assumed that mayonnaise is made up of just water (egg) and oil. But, in reality, you need a little extra help to get these two to blend together. It’s where emulsifiers come in.

It’s virtually impossible to make mayonnaise without emulsifiers. Emulsifiers help mix fats and water. Fats are hydrophobic, they don’t like water and prefer to stick together. Emulsifiers can help overcome that limitation. These special molecules are generally made of a side that likes and a side that doesn’t like water. The part that doesn’t like water will sit in the oil. The part that does like water will sit in the water. This way, it helps the two to meet and stay together.

Without emulsifiers the oil droplets that you mix by whisking/blending would not remain droplets. Instead, they’d very quickly gather together again. The emulsifiers help keep the oil droplets separate for a longer time. The emulsifiers, combined with the high percentage of fat are what keep mayonnaise stable over time.

amphiphilic emulsifiers in action
Example of emulsifiers, for mayonnaise we need the emulsifier on the left-hand side.

Egg yolk contains lecithin

A very commonly used emulsifier, not just in mayonnaise, is lecithin. It is present in ingredients such as soy and sunflower but is especially prevalent in egg yolks. It’s why traditional mayonnaise is made with egg (yolk). The egg serves as the emulsifier.

Acids ‘help’ the egg, and so does salt

Most mayonnaises also contain some sort of acid, some vinegar or lemon juice for instance. Whereas these do change the taste of the mayonnaise, their other crucial role is further stabilizing the mayonnaise. The pH-value of the mayonnaise impacts how well the egg yolk lecithin can emulsify. It actually works best under slightly acidic conditions.

Salt, by the way, can do the same thing, further improving the ‘strength’ of the egg yolk lecithin. However, using too much won’t just make the mayo inedible, it will also destabilize it. Salt can also help slow down oxidation, one of the main shelf-life limiting aspects of mayonnaise.

What about egg-free mayonnaise?

It is possible to make egg-free mayonnaise. But, you will need an alternative emulsifier. This could be a modified starch for instance, or lecithin itself, without the egg. And there are many other ingredients that can do the job, you might have to experiment a little and keep in mind that those ingredients can also influence the flavor of the mayo.

Mustard adds flavor & stability

Traditional mayo recipes often contain mustard. This is added for two reasons. First of, mustard adds some flavor. But even more importantly, it also aids in the stability of the emulsion. Mustard interacts with the fat droplets, making it easier for them to remain dispersed as opposed to joining together.

How mayonnaise spoils

Homemade mayonnaise, made using the recipe below, cannot be stored for long. Raw eggs may contain bacteria that can make you sick, most notably Salmonella. This is why the general recommendation for storage of mayonnaise made with fresh eggs is in the fridge, max. a couple of days.

Store-bought mayo on the other hand can be stored for longer. It generally doesn’t spoil because of microorganisms, but because of oxidation. The oil in mayonnaise slowly oxidizes and turns rancid by exposure to the air (and thus oxygen). It’s also why mayo in an open bottle will slowly turn yellowish. This is not a good sign. The mayo is often still safe to eat, it just might not taste as good anymore.

A scientists’ mystery

You might be surprised to hear that for decades, if not longer, scientists did not fully understand mayonnaise. Of course, cooks and chefs could make it, but scientists simply could not explain why mayonnaise is so thick.

Come to think of it, that is quite strange isn’t it? Mayonnaise is made up of mostly water and oil. Both of which are liquid and flow easily. Mayonnaise, on the other hand, is thick and gloopy.

Scientists still can’t fully explain what happens, but, they’re getting pretty close. They are starting to understand that all those tiny droplets in water make the mayo thick because they are jammed together so tightly. This makes it hard for them to move around. And, for a product to be liquid, the molecules and particles within have to be able to move around sufficiently, to cause the product to flow.

By now, they developed some models and theories as to how these oil droplets interact and jam each other. If you’re interested to learn more, read the article by Wynne in the references below. If not, let’s make some mayonnaise!

homemade mayo

Mayonnaise

Yield: 1 large jar (approx. 300g)
Prep Time: 10 minutes
Total Time: 10 minutes

This recipe leans heavily on the method used by J. Kenji Lopez-Alt from his two-minute mayonnaise. It's the easiest, most fool-proof method I've found for small batches, and fun to do!

Ingredients

  • 1 egg
  • 250g vegetable oil
  • 1 tsp mustard
  • juice of 1/2 lemon
  • pinch of salt

Instructions

  1. Choose a jar that's big enough to hold all the ingredients (at least 300ml) and has a diameter that's just large enough to fit in your stick blender.
  2. Add all ingredients. If they haven't yet come to room temperature, let them do so.
  3. Place your stick blender at the bottom of the jar. Turn it on, using the low-speed setting. The oil will now be pulled down into the egg.
  4. Once no more oil is being pulled down, turn up the speed to high. More oil will now be pulled down.
  5. Once no more oil is being pulled down again, start slowly lifting the stick blender, while still mixing. Continue going up until all the oil has been incorporated.
  6. Your mayo is ready!

Notes

This recipe is very versatile, you can add flavors (e.g. chili flakes, garlic).

References

Mirzanajafi-Zanjani M, Yousefi M, Ehsani A. Challenges and approaches for production of a healthy and functional mayonnaise sauce. Food Sci Nutr. 2019 Jul 18;7(8):2471-2484. doi: 10.1002/fsn3.1132. PMID: 31428335; PMCID: PMC6694423. link

Olsson, V.; Håkansson, A.; Purhagen, J.; Wendin, K. The Effect of Emulsion Intensity on Selected Sensory and Instrumental Texture Properties of Full-Fat Mayonnaise. Foods 2018, 7, 9. https://doi.org/10.3390/foods7010009, link

Wynne, K. (2017) The mayonnaise effect. Journal of Physical Chemistry Letters, 8(24), p. 6189-6192. (doi:10.1021/acs.jpclett.7b03207), link

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