How emulsions work
An emulsion is tiny droplets of one liquid spread through another, like oil in vinegar. Left alone, the droplets merge and the layers separate. An emulsifier such as egg yolk or mustard coats the droplets and keeps them apart.
Add the oil slowly
Add the oil in a thin stream while whisking hard. Each bit breaks into tiny droplets the emulsifier can coat. Dump it all in at once and the droplets are too big and too many to coat, so the dressing splits.
Why emulsions look creamy
A good emulsion looks creamy and cloudy because countless tiny droplets scatter light. Crowded droplets also make it thick. That's why mayonnaise is pale and thick, and why vinaigrette goes cloudy when you whisk it.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Why does a spoonful of mustard help a vinaigrette stay mixed?
It coats the oil droplets and keeps them apart. Compounds in mustard seed coats cling to the droplets and keep them from merging.
True or false: With enough whisking, oil and vinegar will stay mixed forever without an emulsifier.
False. Without an emulsifier the droplets merge and the layers separate again, often within minutes.
What went wrong? You whisk mustard and vinegar, then pour in all the oil at once. Greasy layers form.
The oil went in too fast. Large droplets formed faster than the mustard could coat them, so the dressing split.
Fill the blank: Mayonnaise stays creamy because ___ coats the oil droplets.
Mayonnaise stays creamy because egg yolk coats the oil droplets. Yolk's lecithin and proteins coat the droplets and keep them from merging.
True or false: Pouring the oil in faster makes an emulsion more stable.
False. Adding oil too fast creates large, unstable droplets that split.
Vinaigrette with and without mustard
Does a spoon of mustard hold oil and vinegar together?
Do the 10-minute experiment
