An algae-extracted gelling agent, sodium alginate is used in molecular gastronomy in association with calcium salts for the basic spherification and reverse-spherification processes, whether to make small caviar-like pearls or large ravioles.
The properties of sodium alginate were studied for the first time in 1881 by English chemist ECC Stanford. He had at the time extracted a viscous liquid from brown seaweed of the Laminaria species, with an alkaline solution. He called this product "Algin", a term still commonly used to describe sodium alginate.
Sodium alginate is therefore a salt extracted from the viscous liquid from the cell wall of brown algae. Its natural function is to increase the flexibility of the algae. Thus, algae developing in troubled waters generally have larger alginate content than those growing in calm waters.
Although all brown algae can be a source of alginate, variations in their chemical structure influence the properties of the final product. Different species are therefore harvested according to the purposes for which they are intended and the two most popular are the macrocystis pyrifera of California and the ascophyllum nodosum, grown in the North Atlantic.
The uses of sodium alginate take advantage of two special properties it has. On the one hand, once dissolved in an aqueous solution, sodium alginate has the property of thickening the preparation and increasing the viscosity. On the other hand, when brought into contact with a calcium solution, it forms a gel. This gelling occurs through a cold process, as opposed to the formation of agar-agar gels.
Approximately 50% of the world production of alginate is used by the textile industry where the additive is used as an ink thickener in the printing process.
For its part, the food processing industry uses 30%. The thickening properties of alginate are used for example in sauces, syrups and some products containing milk. It is also used as a stabilizer and anti-settling agent in ice cream and milkshakes, as well as acting as a stabilizer and emulsifier in some salad dressings.
The rest of the production is mainly directed towards the pharmaceutical and pulp and paper industries.
Creative cooking applications
Possible applications of sodium alginate in the kitchen were mostly made known with the popularization of the spherification process by Catalan chef Ferran Adria, of the elBulli restaurant.
By dissolving a small amount of sodium alginate in a chosen alimentary liquid, spheres with jellied edges and a liquid interior can be fashioned. The liquid simply has to be delicately droped in a calcium solution. Alginate and calcium will join to form a gelatinous wall around the liquid sphere thus created so that the spheres will burst in the mouth. They can be served hot or cold, in a mound that reminds of caviar or dispersed in a cocktail.
Tips and tricks
The gel film that forms instantly on contact with the calcium solution will thicken towards the middle of the spheres until they are fully gelled. It is therefore preferable not to let them rest if a liquid interior is desired.
Uniformity and Roundness of the Pearls
For "caviar" that is very round and uniform, position your pipette or syringe parallel to the surface of the calcium bath. The flow of drops will thus be better controlled and the pearls will be round and well defined.
Alginate Solution Disposal
As sodium alginate reacts to calcium, do not pour the excess alginate gel down the sink to avoid blockage. Choose instead the trash or the toilet, which has a larger pipe.
Eliminating Air Bubbles
Air bubbles are often trapped in the preparation during dissolution of the alginate. In order to prevent such bubbles from complicating the spherification process, it may be necessary to let the preparation settle for a few hours.
It is also possible to dissolve the alginate a few hours ahead of time in a small amount of water. The air bubbles will be evacuated during the resting period and the solution will mix well with most preparations. Thus prepared, the spherification solution will not contain any air bubbles.
Choosing a Calcium Salt
It is preferable to use calcium lactate or calcium gluconolactate for all types of spherification rather than calcium chloride. The latter tends to give the pearls a bitter taste, even after being rinsed.
Acidic solutions such as lemon juice and white vinegar can not be spherified because sodium alginate is not soluble at a pH below 3.7. It is however possible to add sodium citrate to reduce the solution's acidity to an ideal pH of about 5 and so allow spherification. For cons, the taste of the final preparation will be altered by sodium citrate.