why does the food colouring separate from the vegetable oil

Why Does Food Coloring Separate from Vegetable Oil?

By Sarah RodriguezNovember 3, 2025

Have you ever July Mixed Colored velvet cake batter for a birthday party only to find that the oil has separated from the food coloring? What's happening here? Let's delve into the science behind this phenomenon.

The separation of food coloring from vegetable oil in cake batter is due to the different densities and specific gravities of the two substances. Food coloring is denser than vegetable oil, which means it weighs more than the oil for the same volume. When these two substances are mixed together, gravity slowly pulls the more dense food coloring down, causing it to separate from the less dense oil.

Understanding Density and Specific Gravity

This separation process can be explained by the concepts of density and specific gravity.

Oil and Water Don't Mix, But Colours Do in this Fun Experiment

an experiment with food coloring in a jar and on the table is a child's hand pouring water into it

Density (ρ) is defined as mass (m) divided by volume (V), which means the compactness of a substance. It is usually measured in grams per milliliter (g/mL). Food coloring has a density of approximately 1.2 - 1.4 g/mL, whereas vegetable oil has a much lower density, around 0.92 g/mL.

The Role of Specific Gravity

Specific gravity (SG) is a comparison of an object's density to the density of a reference substance (usually water, with a density of 1 g/mL). Food coloring typically has a higher specific gravity (1.2 - 1.4) than vegetable oil (0.92), so when the two are mixed, the food coloring naturally begins to sink due to gravity.

Natural Food Dye Guide: How to Make Vibrant, Plant-Based Food Coloring

three bowls with different colored liquids in them and two plastic spoons next to each other

Emulsions: The Key to Stable Mixtures

In contrast, commercially prepared cakes or frostings appear more consistently mixed, often thanks to the use of emulsifiers. Emulsifiers, such as eggs, lecithin, or xanthan gum, help stabilize mixtures by reducing surface tension and binding ingredients together.

Emulsifiers help to create a stable mixture, or 'emulsion,' wherein one liquid is dispersed uniformly within another. By reducing the surface tension between the oil and the food coloring, emulsifiers help to create a homogenized mixture that resists separation.

Eggs as Natural Emulsifiers

One reason why whole eggs or egg yolks are often included in cakes and frostings is that they function as natural emulsifiers. Egg yolks contain lecithin, a type of phospholipid that helps bind water and fat molecules together into a stable, uniform mixture.

When eggs are beaten, they aerate and incorporate air into the batter as well. This aeration and the lecithin in egg yolks both contribute to creating more uniform and stable mixtures. This is why shaking your mixture thoroughly or using an electric mixer can sometimes help to prevent separation or reincorporate the separated food coloring.

Understanding the science behind the separation of food coloring from vegetable oil doesn't mean you have to forfeit vibrantly colored dishes. Instead, you can incorporate the knowledge of emulsifiers, proper mixing, and the relationship between density and specific gravity to create more stable, visually appealing mixtures.