It is common knowledge that immiscible substances such as oil and water will not mix due to the difference in chemical properties. No amount of rigid shaking or mixing will allow such substances to come together. However, in the world of molecular gastronomy and modernist cooking, it is possible to turn heterogeneous substances to a homogenous compound through emulsion.
Although molecular gastronomy did not emerge until the late 1900's, this technique is something which goes back as early as 1674. Recorded in a French cook book is a recipe for beurre de Provence, also known as Aioli, the predecessor of mayonnaise, which is an emulsion. Also known as colloids, such mixtures contain particles which cannot be dissolved, but rather remain suspended due to the different properties of the ingredients used.
This technique can include the use of particles which are solid, liquid or gas. In many cases in the kitchen a mixture of water and oil is what brings about a colloid. In the case of oil and water, one of these two liquids becomes a base while the other becomes dispersed.
The end product of an emulsion may differ according to which substance becomes dispersed. Two main types of emulsions include oil in water and the opposite which is water in oil. When oil is diffused in water the end product may be something like a hollandaise sauce or mayonnaise. On the other hand when water is diffused a common result is butter or a vinaigrette.
An emulsion can either be formed spontaneously or more commonly as a result of movement known as "shearing power" like shaking or mixing. Movement is an important part of the process for many emulsions since it is what disperses the molecules into the base substance. Emulsifying agents may also be used to help stabilize the colloid, binding the liquids together. In cases where the emulsion is not successfully stabilized, components may separate again later on.
Given the diverse properties of many ingredients used in the kitchen, emulsion comes in handy for many different purposes. Fat and water are both common products used in many dishes, as well as in basic cooking components. An oil in water emulsion can be used in the production of creams, sauces, aioli, milk, dressings, cheese and more. On the other hand water in oil emulsion can result in vinaigrettes, margarine, butter, spreads and others.
Other than being able to "bind" immiscible substances like oil and water together, emulsions can also ensure the creation of homogenous mixtures. As a result of this, longer shelf life can be given to a variety of food products. Aside from this, it also allows for the production of creative food products.
Texture and improved taste can also be created through emulsion. Many times the liquids which are combined come together and form various consistencies ranging from soft to hard and smooth. In some cases emulsion can be used to aerate liquids creating air bubbles and foam in food. The foam captures the flavor from the ingredients adding to the taste without contributing any heaviness or overwhelming the base flavors.
The process of emulsion can also be applied in cooking for thickening certain fluids. Regular liquid substances are given body as the fat and water are combined along with other ingredients. As a result the liquids become solidified and can be given shape.
Due to the immiscible nature that fat and water have, putting these together will result in surface tension. Both substances will maintain their characteristics, causing them to separate without blending together freely. Both substances naturally align themselves so that they are grouped together with like molecules and touch unlike molecules as little as possible.
As mentioned earlier incorporating immiscible substances such as fat and water calls for the use of shearing in the form of various movements like stirring, mixing and beating. Often times a whisk or wooden spoon is needed for this process.
This movement serves to help breakdown the substances into smaller particles right from the moment that the whisk or wooden spoon makes contact with the ingredients. The more movement there is the smaller the particles become. The breakdown of substances into smaller particles will allow for these to move less freely as the particles become crammed.As these substances are made to blend together, it can be found in two different phases known as the dispersed phase and the continuous phase.
The dispersed phase refers to the particles which have broken down and have become suspended. The continuous phase is what the holding substance is called. The amount of substances determines which one becomes dispersed and which one becomes continuous.
It should be noted that the more dispersed phase there is then the greater the chance of having the substances separate. Too little space in between the particles may cause them to touch and join together again.
The loss of movement may also eventually cause an emulsion to break. To stabilize this and emulsifying agent can be used. The agent works by coating the dispersed particles with a surfactant that increase kinetic stability.
It should be noted that emulsions are sensitive to both heat and cold. When exposed to increased heat, the molecules tend to move faster and may colloid with each other. On the other hand exposure to cold may cause quick cooling and the formation of crystals which pierce through emulsifying agents as it heats up. Both of these will cause a break down and separation of substances.
The term emulsifiers and stabilizers are often used interchangeably in the culinary world. Food emulsifiers can be classified in two different categories.
Natural Emulsifiers. Derived from plants and animals cells. These are presented as hydrated lypophilic colloids. Examples of stabilizers taken from plants are agar-agar, xanathan gum, mustard, honey and guar gum. Emulsifiers which are derived from animals can come either in the form of proteins such as eggs and soy beans which both contain lecithin. Another animal derivative is cholesterol.
Semi-synthetic Emulsifiers. These are ingredients which occur naturally but undergo processing. These are often taken from naturally occurring fats and oils. Examples of these include methylcellulose and carboxymethylcellulose which are both derived from cellulose. Lecithin naturally occurs in many foods and can be extracted. Semi-synthetic emulsifiers are non-toxic and often work better than natural stabilizers. These are also less prone to bacterial growth.