What it does
The chain contains blocks of guluronic acid, and calcium ions sit between two of those blocks and lock them together. The structure that results is usually described as an egg box. Because the reaction needs only calcium and not heat, a gel can be set at ambient temperature, and because it does not melt on reheating, the gel survives cooking.
Where it works
Restructured and reformed products, where a cold set is the point: shaped seafood analogues, formed fruit pieces, and bake stable fillings that have to hold their shape in an oven. Also as a film former on the surface of a product.
Where it does not
It is sensitive to calcium in the system you did not plan for. Hard water, a calcium fortified base or a dairy ingredient will start the reaction before you want it, and the result is lumps rather than a gel. It also loses structure at low pH over time.
What it interacts with
Calcium above all, then sequestrants, which are used precisely to hold calcium back until the moment of setting. Phosphates will interfere for the same reason.
