Mayonnaise is made from just a handful of ingredients: oil, egg yolk, an acid like vinegar or lemon juice, and mustard. That’s it. The magic isn’t in exotic components but in how those ingredients combine to form a stable emulsion, a creamy suspension of tiny oil droplets in water that shouldn’t hold together but does.
The Core Ingredients
A basic mayonnaise recipe calls for one large egg (or just the yolk), about one cup of neutral oil such as sunflower or canola, a tablespoon of lemon juice or vinegar, a tablespoon of Dijon mustard, a quarter teaspoon of salt, and optionally a pinch of sugar. Every ingredient plays a specific role. The oil provides the body and richness, making up the vast majority of the finished product. The acid adds tang and helps preserve it. Mustard contributes flavor and a little extra emulsifying power. Salt and sugar round out the taste.
The egg yolk is the star. It contains compounds called lecithins and lipoproteins that act as natural emulsifiers, molecules that are attracted to both oil and water at the same time. Without the yolk, oil and vinegar would simply separate. With it, they lock together into something entirely new.
How Oil and Water Stay Together
Mayonnaise is what food scientists call an oil-in-water emulsion. Billions of microscopic oil droplets are suspended in a small amount of water-based liquid (the acid, the water naturally present in egg). Under normal circumstances, oil and water repel each other. The emulsifiers in egg yolk solve this by coating each tiny oil droplet. One end of the emulsifier molecule grabs onto the oil, while the other end faces the surrounding water. This coating prevents the droplets from merging back together.
The proteins and phosphorus-rich compounds in yolk granules physically wrap around the oil droplets, creating a kind of protective shell. That’s why mayonnaise holds its thick, creamy texture rather than collapsing into a puddle of grease. The more finely and evenly those oil droplets are dispersed, the thicker and more stable the mayo becomes.
Why Technique Matters
Knowing the ingredients is only half the story. The way you combine them determines whether you get silky mayonnaise or a broken, oily mess.
The traditional method starts by whisking egg yolks with mustard, a few drops of water, and your acid. Then you add oil in an agonizingly thin stream while beating rapidly. Going too fast overwhelms the emulsifiers. They can only coat so many new oil droplets at once, so flooding the bowl with oil causes the mixture to separate, or “break.”
A faster modern approach uses an immersion blender and a tall, narrow jar. You place the egg, acid, mustard, and salt at the bottom, pour the oil on top, then push the blender head to the bottom of the jar before turning it on. The blades contact the egg mixture first and create a vortex that gradually pulls oil downward into the emulsion. The jar needs to be just slightly wider than the blender head. Too wide, and the oil slips around the sides instead of being drawn into the vortex. If the jar is too big, doubling the recipe to increase the volume of liquid at the bottom can fix the problem.
If your result is watery or loose, the emulsion didn’t form properly. Additional blending won’t rescue it. The best recovery method is to let the mixture separate, then start fresh with a new yolk and slowly drizzle the broken batch in as if it were oil.
What Makes It Safe
Raw eggs raise understandable concerns about Salmonella. The acid in mayonnaise is what keeps it safe. Research on Salmonella survival in homemade mayo found that at a pH of 4.2 or below (roughly the acidity of a well-made batch), the bacteria stopped growing within 24 hours and were eventually killed off entirely. At higher pH levels, closer to 4.6, Salmonella declined more slowly but still couldn’t thrive.
This means using enough vinegar or lemon juice is critical. Australian food safety guidelines recommend a pH below 4.2 for raw egg mayonnaise, paired with refrigeration below 5°C (41°F). Interestingly, older batches of properly acidified mayo actually carry lower risk than freshly made ones, because the acid has had more time to inactivate any bacteria present. If you’re concerned, pasteurized eggs eliminate the risk entirely.
What the FDA Requires for “Real” Mayonnaise
In the United States, a product can only be labeled “mayonnaise” if it meets a specific federal standard. It must contain no less than 65% vegetable oil by weight, one or more acidifying ingredients like vinegar or lemon juice, and an egg yolk-containing ingredient. Products that fall short of the 65% oil threshold or skip egg yolk get labeled “dressing” or “spread” instead. This is why brands like Miracle Whip can’t legally call themselves mayonnaise.
Commercial Mayo vs. Homemade
Store-bought mayonnaise starts with the same basic formula but adds ingredients to extend shelf life and improve consistency at industrial scale. You’ll commonly see modified food starch (a thickener), calcium disodium EDTA (a preservative that prevents the oils from going rancid by binding to metal ions that accelerate oxidation), and sugar in higher amounts than a home recipe. Some brands also use whole eggs rather than just yolks, or add water to adjust texture and reduce cost.
Homemade mayo tastes noticeably fresher, with brighter acid notes and a richer mouthfeel. The tradeoff is a shorter fridge life, typically about one week compared to months for a sealed commercial jar. You also have full control over the oil, which matters for flavor. Extra virgin olive oil makes a peppery, assertive mayo. Avocado oil produces something milder. Neutral oils like sunflower or canola let the egg and acid flavors come through cleanly.
Egg-Free and Vegan Versions
The biggest challenge in making mayonnaise without eggs is replacing the emulsifier. Several plant-based options work surprisingly well. Aquafaba, the starchy liquid left over from cooking chickpeas or other legumes, is the most popular home substitute. It contains a mix of proteins, polysaccharides, and small molecules that can stabilize emulsions and foams in much the same way egg white and whole egg do. Freeze-dried chickpea aquafaba has been tested as an emulsifier in vegan mayo with comparable pH, color, and stability to traditional versions. Soybean cooking water shows similar promise.
Commercial vegan mayonnaises typically rely on soy protein, pea protein, or modified starches as their emulsifying base. The texture can be remarkably close to the original, though the flavor profile is slightly different since egg yolk contributes a subtle richness that plant-based emulsifiers don’t replicate on their own. Many brands compensate with added sugar, extra mustard, or apple cider vinegar for complexity.