One of the classic preparations to have undergone the greatest changes in modern times are gelatins, substances that when heated become a viscous liquid that recovers its original texture on cooling. They are used to give texture to liquids by making it into a gel.

There are many kinds of gelatins obtained in various ways, what changes is the gelling agent used. The gelling agent traditionally used in the past was fish gelatin, in the form of transparent or colored sheets made from sturgeon swim bladder or from the heads of fish such as monkfish or swordfish.

The problem with these was that these animal products do not make stable gelatins when heated.This all changed in the late nineties when Ferran Adrià made a hot cod and black truffle gelatin using Agar-Agar, a natural thickening agent obtained from seaweed and used in Japan since the 18th century.

The very latest in gelling agents for haute cuisine does not come from animals or the sea, but from land. It is Xantana or Gellan, a substance produced by bacteria and an enormously powerful thickening agent.

What are the most commonly used gelling agents?

There are various products available on the market for achieving a wide range of hot and cold gelatins. Each one has its own specific properties in terms of gelling speed and serving temperature.

One of the most popular is Agar-Agar, a natural thickening agent very similar to gelatin and obtained from a type of red seaweed. It can be bought as a powder or as flakes, threads or filaments, it enables acid foods to be gelled and can be used to prepare hot gelatins.  

The gelling agents Kappa and Iota are also extracted from seaweed and have special elastic and firming properties. The former gives a firm, brittle texture, while the latter produces a gel with a soft and elastic consistency.

The gelling family is completed with Gellan, obtained from fermenting starch using bacteria. It produces a firm gel that can be cut cleanly and is able to withstand temperatures of up to 90ºC / 194ºF. Metil is a natural thickening agent obtained from vegetable cellulose. Unlike other gelatins, which become solid when cooled, Metil gels when hot, making it ideal for puddings, fillings and béchamel sauce. 

What dishes use the technique?

Gelling and thickening agents have a multitude of uses. For example, Agar-Agar is used in meat and fish derivatives (pâtés), in dairy products (ice-cream, puddings, sorbets, yogurts), to make sweets and candy, in the drinks industry for clarifying and refining juice and beer, and in the bread making industry for cake icing, fillings and bread dough. Gellan can be used to make liquor syrups, wine coulis and various kinds of jelly.

Paco Roncero is head chef of La Terraza del Casino restaurant (Madrid)