The vinaigrette sauce you’ve tasted at an Italian restaurant is a mixture of oil and vinegar that is not separated, giving it a unique texture that is different from mayonnaise. The main difference between vinaigrette and mayonnaise is the presence or absence of emulsifiers and the type of emulsion they form. Emulsifiers play an important role in bringing together substances that do not mix, such as water and oil, and have applications not only in sauces but also in various industries, such as cosmetics manufacturing.
It’s a family dinner out. You’re in the mood and decide to have pasta at an Italian restaurant. As befits an atmospheric restaurant, the appetizer came with bread and a strange sauce. It’s neither cooking oil nor vinegar, and it’s bluish in color, tempting you to try it. I realized it was a sauce for dipping the bread. Unable to resist my curiosity, I ask the waiter what it is called, and he tells me it’s a vinaigrette. Still suspicious, I spooned some of the sauce and tasted it. The sweet and sour flavor is not bad. I asked the waiter what it was made of, and he told me it was a 1:3 ratio of balsamic vinegar and olive oil.
However, when I first saw it, the balsamic vinegar and olive oil were well mixed, but by the time the main dish arrived, the olive oil and vinegar had separated into two layers. Is it possible to keep them mixed together? The reason vinegar or water and oil don’t mix is because the two liquids with different chemical properties arrange themselves in a way that minimizes the contact area between them. However, with the help of science, it is possible to mix oil in water and water in oil. A quick stir with a hand blender, an electric mixer that you can hold in your hand and whip up into a froth, creates frictional heat to mix the water and oil. This mixture is called an emulsion or emulsified liquid.
In more technical terms, an emulsion is a mixture of two liquids, one of which is insoluble in the other, dispersed in small particles. In practice, the two insoluble liquids are water and oil, so there are two types of emulsions: oil-in-water (O/W), which is oil dispersed in water, and water-in-oil (W/O), which is the opposite.
Another classic example of an emulsion that you can find in everyday life is mayonnaise. Mayonnaise is an O/W emulsion, which consists of oil droplets (cooking oil) dispersed in water (vinegar). So, unlike vinaigrette, how does mayonnaise keep the vinegar and oil separated for so long, even though it’s not a science and you’re not constantly whisking it with a hand blender? The reason is that when making mayonnaise, egg yolks are added as emulsifiers to help the emulsion.
It’s essentially impossible to keep water and oil mixed together, so to create an emulsion, you need to add a third ingredient, a surfactant. In this case, the surfactant is called an emulsifier. The emulsifier added to the oil-water interface refers to adsorption, such as oriented adsorption, in which each molecule of the adsorbed substance is arranged in a certain direction at the interface of the two phases. In other words, it is arranged so that the part that can be mixed with water is close to the water so that water and oil can be mixed) to reduce the interfacial free energy (internal energy existing at the interface) to facilitate emulsification operation, while suppressing the phase separation rate of water and oil to maintain the emulsion state.
The emulsifier changes the phase of the emulsion by continuously changing its HLB (the HLB value is in the range of 0 to 20, and the smaller the value, the stronger the lipophilicity of the molecule as a whole, and the larger the value, the stronger the hydrophilicity), which is called phase inversion of the emulsion.
In other words, the reason why vinaigrette and mayonnaise, which are a mixture of water and oil, look different is because of the way they form an emulsion, that is, the way the water and oil mix. Mayonnaise is an O/W type emulsion, which is oil dispersed in water. In other words, there are tons of oil droplets scattered throughout the vinegar. It’s thanks to the lecithin (a type of phospholipid found in egg yolks) that the otherwise immiscible vinegar and oil are broken down into small particles and mixed together. A vinaigrette, on the other hand, is a spread of droplets in oil. Unlike mayonnaise, this vinaigrette has no emulsifier, which means that it quickly splits into layers of water and oil.
This principle of emulsion is not only used in food, but also in cosmetics. Since the ingredients used in cosmetics contain many substances that do not mix well with each other, emulsification technology is very useful for mixing them in a single formulation. With the development of emulsifiers, many different types of emulsification techniques have been developed to stabilize and modify the properties of emulsified formulations. Starting with the HLB method proposed by Griffin in the 1950s, the PIT method, gel emulsification method, D-phase emulsification method, etc. have been developed, and recently, the use of naturally derived emulsifiers and polymer-based emulsifiers has been increasing as a means to increase skin compatibility or safety to humans. In addition, nano-emulsification, multi-emulsification, liquid crystal emulsification, and Pickering emulsification are being developed and applied to differentiate the appearance of products and increase the delivery efficiency of active ingredients, and research on the application of nanostructured particles such as liposomes and cubosomes is also being actively conducted.
So, while you enjoy your vinaigrette, understanding the science behind it can enrich your dinner table conversations. It’s amazing how small, everyday discoveries can provide us with so much interest and knowledge. In the future, it would be great to talk about these principles over a meal.
