Understanding emulsions is crucial to great sauces and salad dressings. Fats and oils are all hydrophobic, meaning they don't mix with water. But fat molecules like to hang out together which is why your salad dressing forms layers in the bottle, with the fats floating on top of the vinegar, which is about 95% water. But oil and water can be made to mix by making the fat droplets very small and surrounding them with something that prevents them from clumping together called an emulsifier or surfactant. Emulsifiers are molecules that are yentas (if you haven’t seen Fiddler on the Roof, look it up), that can bind with both fat and water. Butter, chocolate syrup, and peanut butter are all emulsions of fat and water. Emulsions are usually thicker than their components and they stick better to foods like salads than the components do on their own.
Egg yolks are among the best emulsifiers. Egg yolks are mixed with oil and vinegar and lemon juice to make mayonnaise, an emulsion that lasts a long time. Hollandaise sauce is a blend of butter and lemon juice also held together by egg yolk.
The molecules of fat or water in an emulsion can bump into their own kind and form larger molecules until the emulsion breaks and the oil and water go hang out with their own tribe again. To prevent this we use stabilizers, molecules that get in the way of fat and water molecules that want to combine. Starches often can do the job. Add a bit of mustard to a vinaigrette, usually after the vinegar and before the oil, and they will mix well and stay mixed, sometimes for days. Xanthan gum is a common stabilizer in commercial food processing and it is often found in commercial salad dressings.
Many sauce or vinaigrette and sauce recipes tell you to dump everything but the oil into a blender or food processor, whup it up, and then drizzle in the oil. I just don’t think this is necessary. The idea of drizzling in the oil stems from pre-blender days when emulsions were made by hand in bowls with a whisk. If you added a little at a time and whisked like the dickens, eventually you got a good emulsion and carpal tunnel syndrome. But a blender is so powerful, you can add the oil all at once and, with a little pulsing, you will get a fine emulsion.
Egg yolks are among the best emulsifiers. Egg yolks are mixed with oil and vinegar and lemon juice to make mayonnaise, an emulsion that lasts a long time. Hollandaise sauce is a blend of butter and lemon juice also held together by egg yolk.
The molecules of fat or water in an emulsion can bump into their own kind and form larger molecules until the emulsion breaks and the oil and water go hang out with their own tribe again. To prevent this we use stabilizers, molecules that get in the way of fat and water molecules that want to combine. Starches often can do the job. Add a bit of mustard to a vinaigrette, usually after the vinegar and before the oil, and they will mix well and stay mixed, sometimes for days. Xanthan gum is a common stabilizer in commercial food processing and it is often found in commercial salad dressings.
Many sauce or vinaigrette and sauce recipes tell you to dump everything but the oil into a blender or food processor, whup it up, and then drizzle in the oil. I just don’t think this is necessary. The idea of drizzling in the oil stems from pre-blender days when emulsions were made by hand in bowls with a whisk. If you added a little at a time and whisked like the dickens, eventually you got a good emulsion and carpal tunnel syndrome. But a blender is so powerful, you can add the oil all at once and, with a little pulsing, you will get a fine emulsion.
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