For 350 years, a traditional ingredient has been used in Japanese kitchens, which has only recently begun to spread timidly in our area, although for now almost exclusively in vegetarian kitchens and in those of some “molecular cuisine” chefs. I'm talking about agar (also called agar agar by some), a gelling agent of plant origin. You can find agar, in powder form, in shops specializing in “natural” products, as well as in those that sell oriental foods.
Agar is extracted from various types of red algae (Phylum Rhodophyta). The two main types of algae used for agar production are Gracilaria and Gelidium. These algae are widespread around the world. Major agar producers are Spain, Chile and Japan.
In Japanese it is known as kanten, which means "cold weather", referring to the traditional method of production.
Widely used in Japan, China, Korea and the rest of the Far East, agar was only introduced to Europe in 1859 by Payen, who presented it to the Paris Academy of Sciences. Curiously in Europe, even before being used for food purposes, it was used as a bacterial culture medium by Robert Koch in his studies on tuberculosis, at the suggestion of his wife Angelina.
Agar is insoluble in the cold but dissolves, when mixed properly, in boiling water. If it is subsequently left to cool, its molecules slowly bind together to form a network that traps the water and the other molecules present, forming a gel, a sort of jelly, when the temperature has reached 30-40 ° C. Unlike the gel formed by starch, this is thermoreversible: it re-melts if heated and reforms by cooling.
The agar gels at very low concentrations, starting from 0.2%. Typical concentrations at which it is used are between 0.5% and 2% with respect to water. Unlike the common isinglass jelly, which is protein in nature, agar gel resists high temperatures, melting only around 85-90 ° C. This allows for interesting culinary applications. You can prepare ravioli with a solid agar filling and an aromatic substance, such as squid ink, which liquefies during cooking. Alternatively, variously flavored gel cubes can be served in a hot broth while maintaining their consistency. It is also widely used by vegetarians instead of animal gelatin. Unlike the pectin used to make jams and marmalades, agar does not need the presence of sugar to gel, and therefore can be used to prepare jams or compotes with a reduced sugar content.
Agar has no flavor and does not interfere with the taste of the food you want to gel. In addition, the human digestive system is able to absorb it only in a small part (less than 10%) so it has a negligible nutritional contribution. To all intents and purposes we can consider it analogous to vegetable fibers. Since agar, unlike common jelly, does not melt at body temperature, it has a different texture on the palate. Plus it is less elastic and more fragile.
It is usually added to the water, stirring vigorously to facilitate dispersion. Having to gel an acid liquid, it is preferable to add it only after having brought the water to boiling, while it is cooling, to minimize the risk of breaking the gelling network (chemists speak of hydrolysis).
The need to boil the agar in water limits its applications to those foods that are not easily altered by high temperatures. If you want to gel a liquid without bringing it to high temperatures, it is advisable to dissolve the agar in a little water when boiling, and add the solution to the liquid to be gelified heated to about 40 ° C. Similarly, it is better to add volatile aromatic components only when the liquid is close to gelation, around 40 ° C
Since the gel is thermoreversible, if you put too little agar for the desired consistency, you can re-dissolve the gel and add more.
Since the agar is not made up of proteins, it is possible to use it in those cases where normal gelatin is not usable, for example in preparations with pineapple or other fruit that contains enzymes that break down proteins (proteolytic enzymes)