Real mayonnaise is made from just a handful of ingredients: vegetable oil, egg yolks, an acid like vinegar or lemon juice, and seasonings. That’s it. The magic is in how these simple components combine into a thick, creamy spread through a process called emulsification, where oil and water-based liquids are forced into a stable blend that wouldn’t normally mix.
The Core Ingredients
Oil is by far the dominant ingredient. To legally be labeled “mayonnaise” in the United States, a product must contain at least 65% vegetable oil by weight. Most commercial American mayonnaise lands between 75% and 82% oil. Soybean oil is the most common choice in the U.S., though sunflower, canola, and corn oil are also widely used. The type of oil matters more than you might expect: it influences the firmness, texture, and how the mayonnaise coats your mouth.
Egg yolks are the second essential ingredient. They serve as the emulsifier, the substance that holds everything together. A natural compound in egg yolks called lecithin has one end that bonds with water and another that bonds with oil, acting as a bridge between the two. You can make mayonnaise with whole eggs, but using only the yolks produces a richer taste and a deeper yellow color.
The acid component is typically white vinegar, lemon juice, or a combination. Commercial recipes use roughly 2.5% to 5% acid by weight. Lemon juice creates a slightly lower pH (more acidic) than wine vinegar at the same concentration, which gives it a sharper, brighter flavor. The acid does double duty: it adds tang and keeps the mayonnaise safe by creating an environment hostile to bacteria. The target pH for commercial mayonnaise generally falls at or below 4.1 to 4.2.
Salt, sugar, and sometimes a pinch of mustard round out the recipe. Mustard powder, used at concentrations of about 0.2% to 0.4%, is more than a flavoring. Its fine particles settle along the boundary between oil and water droplets, forming a physical barrier that helps prevent the emulsion from separating. It acts as a secondary emulsifier and stabilizer alongside the egg yolk.
How Oil and Water Stay Mixed
Mayonnaise is an oil-in-water emulsion, meaning tiny droplets of oil are suspended throughout a water-based mixture of vinegar, lemon juice, and dissolved seasonings. Without an emulsifier, the oil and water would separate within seconds. The lecithin in egg yolks prevents this by coating each microscopic oil droplet, keeping them evenly dispersed.
The size of those oil droplets directly affects how the mayonnaise feels in your mouth. Smaller, more uniform droplets create a smoother, creamier texture with better “lubrication,” as food scientists describe it. This is why technique matters when making mayonnaise at home: adding oil in a slow, thin stream while whisking vigorously breaks the oil into the smallest possible droplets. Dump in too much oil at once, and the emulsion breaks, leaving you with a greasy, separated mess.
The type of oil also changes the structure. Oils with more saturated or shorter fatty acid chains tend to produce a softer mayonnaise with less firmness and lower viscosity. This is why mayonnaise made with olive oil, for instance, has a noticeably different body than one made with soybean oil.
What Commercial Brands Add
A jar of store-bought mayonnaise follows the same basic formula but often includes a few extras to extend shelf life and maintain consistency over months of storage. One common additive is calcium disodium EDTA, a preservative allowed at up to 75 parts per million. Its job is to bind trace metals in the product that would otherwise speed up oxidation, preventing the oil from going rancid and keeping the mayonnaise from developing off-flavors.
Commercial producers also use pasteurized eggs rather than raw ones, eliminating the salmonella risk that comes with fresh egg yolks. The combination of pasteurized eggs, low pH from the acid, and preservatives is what allows a sealed jar to sit safely on a store shelf for months.
Mayonnaise vs. “Mayonnaise Dressing”
The 65% oil minimum set by the FDA is the bright line between real mayonnaise and products labeled as “mayonnaise dressing” or “spread.” If a manufacturer wants to use less oil, they can’t call the result mayonnaise. These lighter products typically substitute some of the oil with water, modified food starch, or other thickeners to mimic the texture. The result is lower in calories and fat but noticeably different in flavor and mouthfeel. The richness people associate with “real” mayonnaise comes directly from that high oil content.
Making It at Home
Homemade mayonnaise requires just egg yolks, oil, acid, salt, and a whisk or food processor. A standard recipe calls for one or two egg yolks, about a cup of neutral oil, and a tablespoon of vinegar or lemon juice. The key is patience: the oil must be added in a very slow drizzle at first, just drops at a time, while whisking constantly. Once the emulsion takes hold and the mixture begins to thicken, you can add oil a bit faster.
The result is noticeably different from store-bought. Homemade mayonnaise tastes brighter and more egg-forward, with a softer, looser texture. It also has a much shorter shelf life because it uses raw egg yolks and lacks preservatives. Kept refrigerated, it stays good for about a week. The pH of homemade mayonnaise varies quite a bit depending on how much acid you add, typically ranging from about 3.0 to 5.1. Keeping the pH below 4.2 and storing it cold are the two most important factors for safety when using raw eggs.
You can customize homemade mayo by swapping in different oils. Avocado oil produces a mild, buttery result. Extra virgin olive oil adds a peppery bite but can turn slightly bitter when emulsified. For the most neutral flavor closest to commercial mayo, a light vegetable or grapeseed oil works best.