A vinaigrette emulsion | Chemistry homework help

While oils and water (or vinegar, which is largely water) don’t mix, it would be useful if they could for the preparation of foods such as salad dressings. You would not want to have one bite of your dinner salad soaked with oil and the next straight vinegar.  A mixture of a quality oil (olive) and red wine vinegar, often flavored with herbs and spices, make up the classic salad dressing known as vinaigrette and will provide a place where we can experiment. 

If oil and vinegar are mixed vigorously, the energy added will break the oil and vinegar layers into small, unstable droplets which will again coalesce and separate into layers over time. This can be less of a problem for the home cook who can quickly toss and serve the salad but can be a problem for commercial salad dressings. Substances called emulsifiers can increase the amount of time before the layers separate. While some commercial emulsifiers are only available through chemical supply houses, home cooks are more likely to use commonly available foods such as eggs, mayonnaise, or mustard. 

Materials and Equipment

• 1 cup vinegar
• 1 teaspoon Dijon (or other brown) mustard
• 1 teaspoon egg yolk
• 3 cups vegetable oil
• Measuring cups and spoons
• 3 small, clear glass jars with screw on lids
• Timer or watch with seconds

Procedure

1. Pour 1/3 cup of vinegar and 1 cup oil  into each jar. Screw the lid on tightly.
2. The first jar will be the control.
3. Add 1 teaspoon of mustard to the second jar.
4. Add 1 teaspoon of egg yolk to the third jar.
5. Shake all jars vigorously for 20 seconds (you can do them one after the other).
6. Time how long it takes each sample for the separate layers to reform. Checking every 15 minutes for a couple hours might be required.  Record the elapsed time and your observations of the mixture (color, appearance, droplet/layer behavior, etc.) on the data sheet.

Note: The vinaigrettes you make here will be edible if you choose. Good olive oil, red wine vinegar, and mustard will give the best results but will cost more than the generic ingredients. As an optional step, taste each recipe to see if you like the taste. (You may need to re-agitate them first.) You can add salt and pepper, dried herbs, or grated cheese if you like. You could also combine them all if the mustard or egg taste needs dilution. While one of these recipes contains raw egg, the amount is small and unlikely to be dangerous but if you are pregnant or ill you may want to avoid eating this.