Agar-agar
Agar-agar is a plant-based gelling agent extracted from red seaweed. It is the main alternative to gelatine and suits vegetarian and vegan desserts.
It behaves fundamentally differently from gelatine. Agar needs boiling to activate: bring it to the boil and hold for around a minute, or it will not hydrate. It sets at a much higher temperature — roughly 35–40 °C — meaning it firms up at room temperature, whereas gelatine needs chilling.
The texture differs too. Agar gives a brittle gel with a clean break; gelatine gives an elastic, yielding one. A set agar gel is thermally reversible: it can be melted again above 85 °C and re-set.
Agar is several times stronger than gelatine by weight, so a direct swap does not work — the dose is calibrated for each application.
Acidic environments weaken the gel, so acid goes in after boiling rather than before.