Sodium alginate and agar agar: different gelling processes

Alginate and agar agar can both structure a preparation, but use different mechanisms. Choosing solely by the term “gelling agent” can easily lead to the wrong method.

Alginate: the role of calcium

Alginate needs dispersing and hydrating in a suitable water-based liquid. Available calcium can trigger gelling: a calcium-rich base or very hard water can therefore cause problems during preparation.

In spherification, contact is controlled to form a membrane. Too long in the bath can change its thickness and the texture of the bite.

Agar: dissolving and cooling

Agar agar needs adequate heating in the water phase. The gel forms on cooling. It is useful for sliceable shapes and films, but alone does not create a membrane with the same liquid centre as reverse spherification.

Agar does not dissolve in pure oil. Even when a recipe contains oil, identify the water phase and how the fat is distributed.

Similar-looking pearls, different results

Drops of agar solution in cold oil gel through cooling. Alginate caviar develops structure through calcium. In the first case, the bite generally gels throughout; in the second, the centre depends on technique and timing.

To choose, read the reverse spherification guide and agar agar guide. A gel’s holding or melting temperatures do not justify exposing any recipe to extreme heat or replace testing during service.