ELI5 science
Why oil and water separate, explained
An emulsion is a crowd of tiny oil droplets suspended in water — or the reverse.
Published
The simple picture
Shake oil and vinegar and you get a temporary snow globe. Stop shaking and the oil floats. Mustard, egg yolk, and some starches are sticky helpers that keep the snow globe from settling as fast.
Why it splits
Too much oil too fast makes huge droplets. Huge droplets find each other. Extreme heat can scramble the helper (egg yolk). Freezing or sitting for days can do the same. Splitting is physics, not a moral failing.
Kitchen takeaway
Add fat gradually. Use a helper. If it breaks, start a new water droplet and whisk the broken mix back in. No nutrition-cure story here — just a sauce that looks like one sauce.