How do commercial salad dressings containing vinegar and oil stay mixed?

Commercial salad dressings containing vinegar and oil stay mixed due to the presence of emulsifiers. Emulsifiers are substances that help stabilize mixtures of liquids that would normally separate, such as oil and water. In salad dressings, emulsifiers prevent the oil and vinegar from separating by forming a bridge between the two liquids and creating a stable emulsion.

Common emulsifiers used in salad dressings include:

1. Egg yolk: Egg yolk contains lecithin, a natural emulsifier that helps bind the oil and vinegar together.

2. Mustard: Mustard contains mustard flour, which acts as an emulsifier and also adds flavor to the dressing.

3. Mayonnaise: Mayonnaise is made from oil, egg yolks, and vinegar, so it naturally contains emulsifiers.

4. Xanthan gum: Xanthan gum is a polysaccharide that is commonly used as a thickening agent and stabilizer in salad dressings. It helps keep the dressing from separating and provides a smooth texture.

5. Soy lecithin: Soy lecithin is a natural emulsifier derived from soybeans. It helps to disperse oil droplets throughout the dressing and prevents separation.

These emulsifiers work by forming a layer around the oil droplets and preventing them from coming into contact with the water molecules in the vinegar. This prevents the oil and water from separating and allows the dressing to remain well-mixed and creamy.

It's important to note that not all commercial salad dressings contain emulsifiers. Some dressings, such as vinaigrettes, rely on the natural thickness of the ingredients and the agitation from shaking the bottle to keep them mixed.