Sodium Alginate

Derived from brown seaweed, sodium alginate is one of the main ingredients used for reverse spherification in this book (see the recipe on page 135). Sodium alginate requires calcium in order to gel. Sodium alginate is combined with cold water and then boiled in order for it to hydrate. It gels cold or hot, as long as there is calcium present. In this book, calcium lactate is used for reverse spherification, but other forms of calcium may be used in simpler ways, such as gently pouring a dairy product directly into a sodium alginate bath. The dairy product or the calcium lactate–laced liquid forms a gel on its surface when it is dipped in the sodium alginate bath, forming a very thin membrane that is quite similar to an egg yolk. The longer it sits in the bath, the thicker this outer membrane gets. It is a thermo-irreversible gel.