Biology – 4.1 Biological molecules | e-Consult

An ethanol emulsion test is used to detect the presence of fats and oils. Fats and oils are insoluble in water but soluble in ethanol. When ethanol is mixed with a sample, and the mixture is vigorously shaken, an emulsion forms. If the substance contains fats or oils, the ethanol will form a milky white emulsion.

This occurs because the fat or oil molecules disperse throughout the ethanol in tiny droplets. The emulsion is formed due to the amphipathic nature of fats and oils – they have both a hydrophobic (water-repelling) and a hydrophilic (water-attracting) region. The hydrophobic regions orient themselves towards the ethanol, while the hydrophilic regions interact with the water, allowing the mixture to disperse.