Mayonnaise is a chemistry trick. The bowl contains a stable suspension of microscopic oil droplets held in a water-based liquid, with each droplet wrapped in a thin coating of egg-yolk lecithin that prevents the droplets from merging back together. The wrapping is what makes the sauce thick and stable. Without it, oil and lemon juice are just two separated liquids in a bowl.
Once that mental model is clear, the entire mayonnaise method becomes obvious. Add the oil slowly at first so the lecithin has time to coat each droplet. Add it faster once the emulsion is established and more lecithin is available. Stop adding when the ratio of oil to water phase gets too lopsided to hold. Rescue a broken emulsion by starting fresh and re-introducing the broken mixture as if it were oil.
What is happening in the bowl
An egg yolk contains lecithin, a phospholipid molecule with a water-loving end and an oil-loving end. Lecithin molecules naturally arrange themselves at the boundary between oil and water, with the oil-loving end pointing into the oil droplet and the water-loving end pointing out into the water. This coating prevents oil droplets from touching each other and merging. As long as every droplet has a lecithin coating, the suspension stays stable.
A large egg yolk contains enough lecithin to coat roughly one cup of oil into droplets small enough for a stable emulsion. Beyond that ratio, there is not enough lecithin to wrap new droplets, the unwrapped oil merges with existing droplets, and the whole emulsion breaks back into a layer of oil floating on a layer of water-egg-acid liquid.
The other key variable is droplet size. Smaller droplets produce thicker mayonnaise because they pack more densely. Whisking vigorously breaks the oil into smaller droplets. A food processor or immersion blender breaks it into very small droplets, producing a thicker stiffer sauce. A wooden spoon stirred slowly produces a thinner sauce because the droplets stay larger.
The basic recipe
For about 1 cup of mayonnaise:
2 large egg yolks (or 1 whole egg for a lighter version) 1 tablespoon Dijon mustard (optional but stabilizing) 1 tablespoon lemon juice or white wine vinegar 1 cup neutral oil (grapeseed, sunflower, or vegetable) Salt and white pepper to taste
The mustard is optional but does two useful jobs. It contributes additional lecithin and emulsifiers from the ground mustard seed. And it adds flavor and a slight tang. Most home recipes include it. Classical French recipes sometimes skip it.
Step by step method (whisk)
Bring everything to room temperature. Cold yolks and cold oil emulsify slowly. Set ingredients on the counter for 30 minutes before starting.
Place the yolks (or whole egg) in a medium bowl with the mustard, lemon juice, a pinch of salt, and pepper. Whisk vigorously for 30 seconds until the mixture is uniform and slightly pale.
Begin adding the oil. Drop by drop at first. Hold the oil container in one hand and the whisk in the other. Drip 2 to 3 drops of oil at a time and whisk vigorously after each addition. The mixture should look thickening and pale yellow within the first 5 to 6 drips.
Once the mixture is visibly thickened (a tablespoon or two of oil incorporated), increase the oil stream to a thin trickle. Continue whisking vigorously. The emulsion gets thicker and paler as more oil goes in.
After about half a cup of oil, the stream can become a thicker drizzle. Keep whisking. By the time all the oil is incorporated, the sauce should be glossy, pale, and stiff enough to hold a soft peak.
Adjust seasoning. Add more salt, lemon juice, or mustard to taste. If the sauce is too thick, thin with a teaspoon of warm water whisked in.
Step by step method (immersion blender)
The immersion blender method is fast and reliable. The narrow blender cup creates ideal turbulence for the emulsion to form.
Combine all ingredients (yolks, mustard, lemon juice, salt, pepper, AND the full cup of oil) in the narrow cup that came with the immersion blender. Let everything settle for 30 seconds.
Place the immersion blender on the bottom of the cup, completely covering the egg yolks. Switch on and hold steady at the bottom for 10 seconds. A pale emulsion forms underneath the blender head and starts climbing up the cup.
Slowly raise the blender head over the next 10 seconds, allowing the oil at the top to incorporate into the emulsion as you go. The whole jar becomes thick mayonnaise in about 20 seconds total.
This method works because the blender blades create such intense local turbulence at the bottom of the cup that the emulsion forms instantly without the slow drip-by-drip technique.
Aioli (with egg yolk)
Modern aioli is essentially garlic mayonnaise made with olive oil. The method is identical to mayonnaise but with two additions and one substitution.
Method. Crush 2 to 3 cloves of garlic to a smooth paste with salt in a mortar and pestle, or grate on a Microplane. Add to the egg yolks at the start. Use a 2 to 1 mix of mild olive oil to extra virgin olive oil instead of neutral oil. Finish with an extra squeeze of lemon juice. Serve with grilled fish, roast potatoes, or crudites.
The classical Provencal aioli without egg is a different and more difficult preparation. Crushed garlic and olive oil are pounded together in a mortar with salt, and the emulsion is held by the small amount of water in the garlic plus the natural emulsifiers in the garlic cells. This version breaks easily and is best made by an experienced cook with a marble mortar.
Rescuing a broken emulsion
A broken mayonnaise is recoverable in 30 seconds. The technique:
In a fresh clean bowl, add 1 teaspoon of warm water and 1 teaspoon of Dijon mustard (or 1 fresh egg yolk for a fuller rescue). Whisk briefly.
Slowly whisk the broken mixture into the fresh bowl, drop by drop at first, the same way you would add oil to start a new batch. The lecithin in the fresh yolk (or the emulsifiers in the mustard) re-coats the oil droplets and reforms the emulsion.
After about half the broken mixture is incorporated, the stream can become a steady drizzle. By the time everything is in, the sauce is back to a stable mayonnaise.
Common failure modes
Broken emulsion. Oil added too fast at the start, or oil-to-yolk ratio pushed past 1 cup of oil per yolk. Rescue with the technique above or start fresh.
Thin runny sauce. Not enough oil incorporated, or the whisking was too slow to break the oil into small droplets. Continue whisking and adding oil. The sauce thickens as more oil goes in.
Bitter taste. Pure extra-virgin olive oil was used. The peppery bitter compounds in extra virgin olive oil become more pronounced when the oil is broken into tiny droplets and aerated. Switch to a milder oil or cut extra virgin with neutral oil in a 1 to 3 ratio.
Greenish or grayish color. Iron from a cheap metal bowl reacted with the egg yolk. Use a glass, ceramic, or stainless steel bowl.
Mayonnaise made fresh at home is dramatically better than commercial bottled mayonnaise, lasts about a week refrigerated, and takes 4 minutes start to finish with an immersion blender. The technique is one of the most rewarding to learn in a home kitchen because it converts a five-cent egg yolk and a quarter cup of oil into a sauce that elevates a sandwich, a poached fish, a roast chicken, or a plate of crudites.
Frequently asked questions
What is the difference between mayonnaise and aioli?+
Strictly, aioli is a Provencal sauce of garlic, olive oil, and salt pounded in a mortar without egg, while mayonnaise is an egg-yolk emulsion of oil into vinegar or lemon juice. In modern usage, especially in the United States, aioli has come to mean a garlic mayonnaise. Both rely on the same emulsion chemistry once egg yolk is involved, but a true Provencal aioli without egg is much harder to stabilize.
Why did my mayonnaise break?+
Two common causes. The oil was added too fast at the start, before the emulsion had enough lecithin coating to absorb the new droplets. Or the ratio of oil to water-phase ingredients was pushed past about 8 to 1, beyond which there is not enough water phase to hold the oil. Fix a broken batch by starting a fresh egg yolk in a clean bowl and slowly whisking the broken mixture into it as if it were oil.
Can I use a whole egg instead of just yolks?+
Yes, with a different result. Whole-egg mayonnaise (the version used in most American food processor recipes) makes a lighter, fluffier mayonnaise because the egg whites add water and air. Yolk-only mayonnaise (the classical French version) makes a thicker, richer, deeper-yellow sauce. Use 2 yolks per cup of oil for the classical version, or 1 whole egg per cup of oil for the lighter version.
What oil works best for mayonnaise?+
A neutral oil (grapeseed, sunflower, or refined vegetable oil) gives the cleanest flavor and lets seasonings come through. Pure olive oil makes a peppery, assertive mayonnaise that is correct for aioli and Provencal cooking but can overwhelm sandwiches. A common compromise is 3 parts neutral oil to 1 part extra virgin olive oil, which gives mild fruitiness without bitterness.
Is homemade mayonnaise safe with raw eggs?+
The risk is low with fresh clean eggs from a trusted source but is not zero. Salmonella contamination in the US shell-egg supply is roughly 1 in 20,000 eggs. To eliminate the risk, use pasteurized shell eggs (sold in most supermarkets in the dairy aisle) or pasteurized liquid yolks. The acid in lemon juice or vinegar also reduces bacterial growth over the storage life. Refrigerate immediately and use within 4 days.
Priya Sharma
Priya Sharma writes for The Tested Hub.