What is it?
Agar is a vegetarian gelling agent derived from dried seaweed. Although some agar is wild harvested, it is more commonly farmed commercially.
Like gelatine, agar is thermo-reversible but at much higher temperatures, and it has around 5 times the setting properties – so much less is needed. Unlike gelatine, agar sets at room temperature but will hold its shape when hot.
How does it work?
It forms a ‘framework’ that holds liquid molecules in place. A 1.5% solution of agar forms a gel on cooling to room temperature that does not melt below 85º C. This is a novel property of agar that finds many uses in food applications.
The gel strength of the agar is influenced by concentration, time, pH, and sugar content. The pH noticeably affects the strength of the agar gel; as the pH decreases, the gel strength weakens. Sugar content has also a considerable effect over agar gel. Increasing levels of sugar makes gels with a harder, more yielding texture.
How should it be used?
Mix the agar with the liquid to be gelled and bring to the boil, whisking all the time till completely dissolved. Remove from the heat and allow to cool. It will remain a liquid until it cools to 35º C at which point it will begin to gel. The gel will remain solid until it is heated again to 85º C.