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The Chemistry Behind Mayonnaise (Recipe Included)

Updated: Oct 3, 2020

We all know about mayonnaise, it comes with our burgers, on salads, maybe with fries, but what most of us don't know is the chemistry and science behind what makes mayo, well, mayo.

Mayo consists of eggs, acid, and oil. Simple as that. But if you were to just put oil, acid and eggs in a bowl and whisk them, you would be left with a greasy heterogeneous mixture of oil and egg. This is because egg yolk has water, and water and oil separate.

Mayo is an emulsion, held together by lecithin, a fat commonly found in soybeans and egg yolks. Lecithin is amphiphilic, meaning it contains both hydrophobic and hydrophilic properties. Water and oil separate, because oil is hydrophilic, but lecithin brings water and oil together, forming a stable emulsion of egg yolk and oil.

Oil separates because oil molecules come together and join and float to the top. Lecithin prevents that, by coming in between each oil molecule, preventing the molecules to join. This prevents the oil from separating.

You may notice that when making mayo, you must slowly stream in oil. This is because the lecithin must coat each oil droplet so the oil molecules do not come together. If the lecithin does not thoroughly coat each oil molecule at the beginning, the mayonnaise splits.

If your mayonnaise breaks, there is a fix. Take a new bowl and add an egg yolk. Slowly drizzle in the broken/split mayonnaise into the egg yolk and start over. The mayonnaise should slightly thicken and after about 5 minutes of whisking, you will be left with thick, creamy mayonnaise.

Food safety: Raw egg always brings up a concern of food safety. Some raw egg has salmonella, a food-borne bacterial disease that can cause uneasiness in the stomach and intestinal area. Serving raw egg to elderly, vulnerable, or children is probably not a good idea. For an alternative mayonnaise, sous vide the eggs for 2 hours in 135ºF - the eggs will be rid of their bacteria and safe to eat. The eggs might look a little cloudy, but they function just as well.


1 egg yolk

3/4 cup neutral tasting oil (canola, vegetable, ground nut)

1/2 tsp salt

1/4 tsp pepper

1 tbsp dijon mustard

Half a lemon, juiced

1/4 tsp smoked paprika (optional)

  1. Place egg yolk in a bowl. Slowly stream in the oil (drop by drop) into the egg while whisking vigorously. After 1 minute, the egg should have slightly thickened. Now, you can add the oil in more gradually, but remember to whisk vigorously.

  2. After you have added 1/2 cup of oil, add the rest of the ingredients.

  3. Continue adding the oil slowly until no oil is left and the mayonnaise is thick and creamy.

  4. Serve with toast or combine with garlic to make an aioli.

  5. Enjoy!

This post was made possible by my chemistry teacher, Dr. Keith Karraker, who taught me exactly what makes mayonnaise an emulsion. Thank you.

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