Grades 3–5 · Everyday Life
How does mayonnaise keep oil and water together?
Oil and water usually separate into layers, but mayonnaise keeps a great deal of oil distributed through watery ingredients. Its texture comes from many tiny oil droplets packed closely together. This type of mixture is an emulsion.
In the diagramCoatings keep tiny oil droplets from mergingenlarged oil-in-water emulsiongreen: stabilizing coatingblue: watery surroundingsSeparate oil droplets are held within watery material.
Mixing breaks the oil into small droplets. By itself, that is not enough to keep them apart for long. Droplets that meet can join into bigger drops, eventually producing separate layers again.
Egg yolk supplies substances that gather at the boundary between oil and water. They help coat the droplets and make merging harder. Lecithin is one of these emulsifying substances, and yolk proteins also contribute.
The oil has not dissolved into a true solution. It remains in separate tiny droplets, with watery material between them. Their size, close packing and protective coatings help explain why the mixture is thick and appears uniform.
About this explanation
Starting knowledge: Know that oil and water tend to separate and that a mixture can contain very small pieces.
Sources
- UCLA Department of Chemistry and Biochemistry — Illustrated Glossary of Organic Chemistry: Emulsion