What is the role of mustard in a vinaigrette?

• A. It acts as an emulsifier that helps bind oil and water
• B. It thickens the dressing like a cream
• C. It adds sweetness
• D. It kills bacteria

Answer: (A)

Emulsification is what keeps oil and water from separating in a vinaigrette. Mustard acts as the emulsifier, thanks to compounds in mustard seeds that help oil and water-based components mix and stay dispersed. When you whisk mustard with the vinegar (then slowly whisk in oil), the oil forms tiny droplets that stay suspended in the watery phase, creating a stable emulsion. This yields a smooth, cohesive dressing that won’t separate quickly. It’s not about thickening like cream, adding sweetness, or killing bacteria—the key role here is binding the oil and water into one stable mixture.