Emulsification
What do chocolate, mayonnaise, salad dressing, milk, butter and ice cream have in common? All of them are Emulsions!
What happens when oil and water mix to create stable substances like mayonnaise, salad dressing, and even milk? It is Emulsification!
You know that oil and water do not mix. Shake them together vigorously, and they seem to combine — until you stop. However, this combination is not “true in micro”!
By definition, emulsions are part of a more general class of two-phase systems of matter called colloids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include milk, mayonnaise, and vinaigrettes.
We can also describe emulsion in a another way. For instance, a liquid can trap air bubbles and turn it into a foam. It is possible to incorporate air bubble into a liquid by just whisking vigorously. Although this phase is highly unstable and the air could escapes in a relatively short time, emulsifiers can be incorporated into the solution to avoid this instability. For example in molecular gastronomy, emulsification is a popular technique used to incorporate and stabilise air bubbles in a liquid mixture.
Your naked eye can only see a homogeneous product. But things are quite different if you check them under the microscope, where thousands of small droplets dispersed in a second liquid substance can be seen. In each case, two substances that are normally immiscible, oil and water, have been mixed using an emulsifying agent – emulsifier. The function of emulsifiers could be defined as: to suspend bits of oil in water — or vice versa — and keep them there. In layman’s terms, the oil, broken into smaller bits via your brute force, is suspended briefly in water. Once the force is over, they separate once more.
An emulsifier is a substance that stabilises an emulsion by increasing its kinetic stability. One class of emulsifiers is known as “surface active agents”, or surfactants.
Coming back to our daily life, egg and milk protein, bread starch, gelatin and cream fat are commonly seen emulsifiers that have used in traditional cuisine for a long time. These products are also called surfactants, a word derived from “surface active agents,” since their molecules act as a barrier (interface) between water and air. Additionally, in recent years the food industry did a lot of research effort in this field and discovered some new emulsifiers, soy lecithin and methylcellulose are the most two famous among them.
These emulsifiers (or food additives) bring great pleasure to molecular gastronomy enthusiasts by reducing the tension between the water and air surface, which stabilises the air and foam. In the following paragraphs, soy lecithin will be used as the example to explain what was exactly happening in microscopic level:
LECITHIN MOLECULE: The lecithin molecule looks like a hydrophilic pinhead, attracted by water, with two hydrophobic fatty acid legs that are repelled by water.
AIR BUBBLES FORMATION: The lecithin molecule positions itself around air bubbles, which inflate their hydrophilic portion towards the water. The air bubbles’ surface is surrounded by lecithin molecules, thus preventing water from escaping from the liquid, which would deflate the foam.
The key factor of deciding whether a foam is stable formed or not is the amount of air bubbles dispersed inside the liquid phase. In general, a foam containing a larger number of small air bubbles is most likely to be more stable than which formed using a small number of large bubbles. A large amount of bubbles dispersed in the liquid also increases the viscosity of solutions, which gives foams their creaminess. Although their viscosity increases the stability, foam and air remain relatively unstable. As a result, air bubbles will gradually escape from the liquid phase in which they were incorporated.
Three main causes accelerate this phenomenon. 1) The air can easily dissolve in liquids and evaporate. 2) The internal pressure of very tiny bubbles increases as their size decreases, eventually causing their membranes to burst. 3) As there is a significant difference between the density of fluid and air, the two phases tend to separate, and liquid will gradually migrate to the bottom of the dish.
Among all emulsifiers introduced, some of them are more effective than others. Egg yolks do a particularly good job, due to a protein called lecithin, which has held together centuries of hollandaise sauces and countless aiolis. Mustard is a classic choice for vinaigrettes. Mayonnaise is effective as well — not surprisingly, since it is a yolk-stabilised emulsion. Try whisking a little bit into your next salad dressing.
Adding too much of the dispersed phase to a given emulsion is only one of many reasons an emulsification will “break.” In fact, emulsifications are unstable by nature. Water and oil will always attempt to re-create their natural surface tension, but this inevitability can be prevented by using emulsifiers and stabilizers.
Gelification
Gelification is defined as the process of turning a substance into a gelatinous form. During gelification process, substances in liquid state will be transferred into solids state, with the help of gelling agents. Common gelling agents come from natural sources and include gelatin, gellan gum,agar-agar, methyl-cellulose, Carageenan and pectin.
All of these are hydrocolloids and reactive if dispersed in liquids. Gels resulting from this process may range from tough and hard to weak and soft. Gels are characterized by having a viscous property when heated and becoming solid or jelly like once cooled. Melting and cooling points for gelling agents may differ according to type.
The formation of a gel can simply be defined as a change from liquid to solid state, and serves as one of the most popular technologies in industry. However, there is a tendency to disregard the great diversity of gels that can be made in cooking. Depending on the nature and concentrations of the gelling agent being used, the gel texture can range from supple and elastic to firm and brittle. This enables inventive cooks to experiment and attain the exact desired texture!
Despite the wide range of possible textures, gelification process involves a rearrangement of the molecules that align and attach themselves until they form a network that traps the liquid. This network looks like meshes of a net that keep all of the particles in suspension, preventing their aggregation and the collapse of the structure.
Several well-known molecules are able to form gels and could be found everywhere: flours, tapioca or corn starch, eggs and gelatin. However, non-traditional gelling agents are becoming more commonplace in the market and are widely used in molecular gastronomy: hydrocolloids.
Hydrocolloids:
The definition of hydrocolloid is not quite established, but the origin of the word greatly helps to understand the meaning. Hydrocolloids become hydrated in water (hence the prefix “hydro”). Once the colloidal solution formed, it hinders the mobility of water until it becomes thickened or gelled. The long molecules that join together to form a gel through various preparation stages are called polymers.
The use of hydrocolloids in cooking makes it possible to form gels with various textures at temperatures, pH values and with foods that are impossible to gel with common gelling agents. In addition, the concentration needed to achieve the desired result is often lower, which is a significant advantage that avoids huge changes in flavor. So it is not surprising to find these texturizing agents in a whole range of consumer products.
There are many different types of hydrocolloids, most of which have different sets of properties. In particular, two of the most commonly used will be discussed in details:carrageenan and agar agar.
Carrageenan is an extract from red algae. There are three types of carrageenan: iota, kappa, and lambda same in origin but different in properties: 1) Iota carrageenan makes flexible, elastic gels in the presence of calcium ions. It is is fairly clear, but does not dissolve in cold water. As such, the solution must be heated to over 60 degrees Celsius to dissolve the carrageenan fully, and it will gel as it cools down. 2) Kappa carrageenan forms firm but elastic gels in the presence of potassium ions and brittle gels in the presence of calcium ions. The solubility and gelling processes are the same as iota carrageenan. It can be thinned with sugar and is thermo-reversible. 3) Lambda carrageenan is not used for forming gels; rather, it is used solely as a thickening agent.
Agar agar is a hydrocolloid that forms heat-resistant gels while cooling between 32 and 43 degrees Celsius. It is able to retain its firmness up to about 85 degrees Celsius, or 185 degrees Fahrenheit, making it the optimum additive to make gels designed to be consumed while hot. The firmness of these gels is directly proportional to the concentration of agar agar. High concentrations yield firm, brittle gels, while low concentration gels are “supple and fragile” (KitchenTheory.com). Agar agar is a very diverse hydrocolloid, also used to thicken pie fillings because of its heat resistance, stabilise ice creams in conjunction with other vegetable gums, create foams when put into a siphon. It is soluble only in water, not in alcohol or non-polar liquids.
Mechanism of gelification could be roughly divided into several steps:
1. DISPERSION is an important step during the formation of a gel. An improperly dispersed gelling agent will stick together and form lumps that will alter the subsequent formation of the gel. Dispersion must allow the gelling agent molecules to be completely surrounded by water by separating the powder particles. For several hydrocolloids (agar-agar, carrageenan, sodium alginate, gellan gum), this requires vigorous stirring of the mixture with cold water.
DISPERSION: Initially, the hydrocolloid particles dispersed in water detach from each other, thus allowing liquid to penetrate into and swell the molecule, and then dissolve.
2. HYDRATION then allows water to penetrate inside the hydrocolloid molecules, which then facilitate reactions, as it is surrounded by water and suspended in the solvent. This step can be done by gradually heating or chilling the liquid. Agar-agar, carrageenans, some gelatins and gellan gum require heating to hydrate. Alginate hydration requires cooling; the process is described in detail in the section on spherification.
HYDRATION: Molecules dispersed in the solution are essentially linear polymer chains with few similarities among them at this stage. Once hydrated, the long molecules no longer have any defined structure and are rather randomly organized in the solution.
3. FORMATION of most hydrocolloids occurs after hot hydration, when the temperature drops to a gelling temperature that is specific to each additive. Although some gels are formed before reaching room temperature, others require refrigeration.
FORMATION: As the solution cools, the polymer chains twist together and form double helices with other molecules while bonding one molecule to another.
In conclusion, gelification has been around for years, and it has undergone a lot of changes in terms of use. In the modern kitchen the gelification technique has many different uses. It can serve to stabilize liquids without affecting taste. It may also be used for suspending food particles and creating various shapes for aesthetic purposes. Lastly, it can also be used to create various textures and improve dining experiences.
For references used in this post, please refer to the References tab.