Using agar agar gels

What it is

Set at room temperature, this seaweed-derived gel stays firm even when warmed back up to around 35°C, which means a jelly made with it will hold its shape on a hot summer day where gelatine would melt into a puddle. That heat resistance, unusual among gelling agents, is exactly what makes it so useful.

Using agar agar gels is the practice of setting liquids into gels using agar, a gelling agent extracted from red seaweed, widely used as a plant-based alternative to gelatine. Agar produces a firmer, more brittle gel than gelatine's soft wobble, and it sets and holds at temperatures where gelatine would not, which opens up techniques like hot gels and clear jellies that keep their shape on the plate. It has long been a staple in Asian desserts and is central to plant-based and modernist cooking alike.

The science is in how agar behaves with heat. Unlike gelatine, agar must be brought to a boil to dissolve fully, then it sets as it cools below around 40°C, forming a thermo-stable gel. This means an agar gel can be cut into clean shapes, layered, and even briefly warmed without collapsing. The firmness is adjusted by the amount used, with more agar giving a denser, more sliceable result.

Most people start by setting a simple fruit juice into a firm jelly and are struck by how different the texture is from gelatine, cleaner and more sliceable. The honest trade-off is that agar's brittle, firm set is not to everyone's taste where a soft wobble is wanted, and the exact ratio takes a little testing. But it sets fast, holds well, and suits vegetarian and vegan cooking where gelatine cannot be used.