Store-bought mayo has its place, but homemade is a different animal. Brighter, fresher, and you control what goes in. Martha Stewart walks through the classic method in a five-minute video, and the move that matters is emulsification: pulling oil and a little liquid into something thick, silky, and stable.
One egg yolk, a teaspoon of Dijon, a teaspoon of lemon juice, and a cup of neutral oil. The yolk does the work, because it's full of lecithin - the natural emulsifier that keeps the oil droplets suspended instead of pooling back together.
What's actually happening in the bowl
Oil and water don't mix. An emulsion forces them to by breaking the oil into droplets small enough to stay scattered through the water, then coating each droplet so it can't merge with its neighbours. Lecithin from the yolk does the coating. Your whisk does the breaking.
That's why the oil goes in slowly. Add it faster than the whisk can break it up and you get large droplets that find each other and separate. Once you understand that, every rule below stops being arbitrary.
Why room temperature matters
Cold yolk and cold oil are both more viscous, and cold fat resists breaking into fine droplets. A fridge-cold yolk is the single most common reason a first attempt splits.
Take the egg out 30 minutes ahead. In a hurry, sit the whole egg in warm tap water for five minutes.
Choosing the oil
Use something neutral - grapeseed, sunflower, safflower, or a light vegetable oil. Extra-virgin olive oil makes mayonnaise that tastes aggressively bitter, because whisking drives the polyphenols in the oil into a form your tongue reads as harsh. It gets worse as it sits.
If you want an olive flavour, make the mayo with neutral oil and whisk in a tablespoon of good olive oil at the very end.
Fixing broken mayonnaise
Split mayo looks thin, greasy, and curdled, with visible oil. Nothing is wasted and you don't start over.
- Put a fresh egg yolk, or a teaspoon of warm water, in a clean bowl.
- Whisk the broken mixture into it a few drops at a time, exactly as if it were the oil.
- Once it starts to thicken and hold, pour a little faster.
You're rebuilding the emulsion around a new base. It works nearly every time, and the result is indistinguishable from mayo that never broke.
If it's too thin or too thick
Too thin usually means not enough oil went in, or it went in too fast. Keep whisking and add oil more slowly.
Too thick, and it will look stiff and slightly grainy. Whisk in warm water half a teaspoon at a time. Water, not more lemon juice, unless you want it sharper.
Storage and the raw egg question
Homemade mayonnaise keeps about a week in a sealed jar in the fridge. It contains raw yolk, so it doesn't have the shelf life of a commercial jar, which is made with pasteurised egg and preservatives. Label the jar with the date.
Anyone pregnant, elderly, very young, or immune-compromised should use pasteurised eggs, sold in the shell at most supermarkets. The acid from the lemon juice helps but doesn't make raw egg safe on its own.
Common questions
Can I use a whole egg instead of just the yolk?
Yes, and it's easier with an immersion blender. Whole-egg mayo is lighter and paler. By hand, the yolk alone gives a thicker result.
Why is my mayo bitter?
Almost always the oil. Extra-virgin olive oil turns bitter when whisked. Dijon can add a little sharpness too, but it doesn't taste bitter the way over-worked olive oil does.
Can I make it in a blender or food processor?
An immersion blender in a narrow jar is the most reliable method there is - put everything in at once, lower the blender to the bottom, run it, and lift slowly as it thickens. A full-size food processor works but tends to warm the mixture.
Can I flavour it?
Whisk additions in at the end: grated garlic for aioli, chipotle in adobo, lemon zest, or chopped herbs. Adding them at the start interferes with the emulsion.
