What it actually is
An emulsion is not a stable state, it is a delayed one. Droplets of oil want to find each other and separate. What keeps them apart is a film at the interface, built by an emulsifier or by protein, and the smaller and more uniform the droplets the slower the separation. Failure arrives as creaming, as coalescence, or as the slow growth of large droplets at the expense of small ones.
Why it matters
Separation is an immediate reject. Unlike most defects it is also obvious through the pack, so it is found by the customer rather than by quality control.
What changes it
The emulsifier and its level, droplet size achieved during processing, pH, salt, the temperature the product sees in distribution, and time. A warm warehouse does in weeks what a cool one does in months.
