Sodium alginate, along with calcium chloride, is one of the most widely distributed molecular gastronomy ingredients in the world. Why? Simply because it is the basis of the popular technique known as spherification—or encapsulation. Spherification produces fruit caviar.
Alginate can be found in and is derived from the cell walls of brown algae.
Reaction with calcium chloride
Alginate itself is an ion—basically a molecule dissolved in water, so pure alginate in a solution of water can be referred to as alginic acid. When alginate ions interact with calcium ions, they “condense”—precipitate—into a solid. The great part about such reaction is that we can manipulate it to create a film between two liquids. When one liquid containing alginate, such as a droplet of fruit juice, comes in contact with another liquid containing calcium, a film forms around the liquid containing alginate. Of course, to conduct such cooking experiment, you need to dissolve the right amounts of alginate and calcium into the two liquids.