The formation of a gel is one of the most common techniques in the 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, the formation of a gel can simply be defined as a change from liquid to solid state. This 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. The most traditional are 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
The use of hydrocolloids in cooking makes it possible to form gels with various textures at temperatures, pH levels 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 excessive changes in flavor. So it is not surprising to find these texturizing agents in a whole range of consumer products. 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 has 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 strength and type of connections determine the characteristics of the gel.
As with all culinary techniques, to successfully make a gel using hydrocolloids requires precision and compliance with certain key steps. Considering how easy it is to make instant puddings, this seems a bit excessive, but to guarantee success, there is no room for carelessness!
Dispersion is an essential step for the formation of a gel and for the thickening of a preparation. 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.
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.
The gel’s final texture varies greatly from one hydrocolloid to another, but several other properties specific to each of the additives can also influence the selection in the development of a recipe.
The strength of bonds between polymer chains influences the gel’s texture in the mouth. However, it should also be noted that some hydrocolloids form gels in the presence of ions, such as calcium, magnesium, or potassium. Carrageenans and gellan gum are good examples, making these additives a preferred choice in dairy-based products. Sodium alginate, on the other hand, only reacts in the presence of calcium ions. For more details, read the section on spherification.
The melting point of gels is another characteristic that can be exploited in cooking. A gel obtained from gelatin will melt at a
temperature of 99°F (37°C), the same temperature as the human body. Gelatin-based jellies thus create a melt-in-the-mouth sensation. In contrast, agar-agar-based gels have a melting point around 194°F (90°C), which gives these dishes the significant advantage of being able to be served hot.
It should also be mentioned that some hydrocolloids simply have no melting point. The resulting gels are called thermoirreversible, that is, once the bonds between the polymer chains have formed, they cannot be broken. For example, gellan gum-based gels will never melt at temperatures used in cooking and may therefore even be incorporated into stewed dishes!
The gel solution’s acidity can also affect the result and therefore some gels do not congeal in the presence of highly acidic ingredients. It is also important to note that the degree of transparency of gels will vary based on the gelling agent chosen. Agar-agar will usually produce cloudy gels, whereas kappa carrageenan and gellan gum will produce gels whose transparency ranges from slightly opaque to opaque. Finally, sodium alginate, gelatin and iota carrageenan produce completely clear gels.