What Is Agar Agar and How to Use It in Pastry – Complete Guide
Beyond flavour, texture is the most important element of a dessert – and often what makes the difference between one we love and one we don’t. Think of a dark chocolate mousse: light, airy and delicious. Now imagine the same mousse, with the same flavour, but with a jelly-like, rubbery texture. The taste hasn’t changed, yet the experience is no longer memorable.
I have written a detailed guide to gelatin before, but agar agar deserves its own article. It is often presented as the vegan alternative to gelatin, and while both are used for similar purposes, they are very different in origin, composition and use.
What is agar agar?
Agar agar is a plant-based (vegan) gelling agent extracted from seaweed. It comes as a powder, flakes or bars and originates in Asia, where it is traditionally used in puddings, jams and other desserts. It is extracted from several species of red algae (class Rhodophyceae); seaweeds that contain agar are called agarophytes. How much agar they contain depends on factors such as the carbon dioxide concentration and temperature of the water and the intensity of sunlight.
Legend has it that agar agar was discovered around 1658 in Japan by Mino Tarozaemon, an innkeeper near Kyoto, who threw out some leftover seaweed soup and noticed that it had set into a jelly in the cold night air.
Properties of agar agar
- Strong gelling power – a small amount is enough to create a firm gel.
- High melting point – agar jellies and gels don’t melt at room temperature.
- High setting point – agar starts to set at a much higher temperature than gelatin, and much faster.
- Brittle, slightly creamy texture – unlike gelatin, which gives elastic jellies.
- Thermoreversible – like gelatin, it can be reheated without losing its properties.
- Transparent – the resulting jelly or gel is clear.
How to use agar agar
- Weigh it exactly as the recipe says. You will sometimes read that agar agar can be used in the same amount as gelatin – that is far from true. Agar sets much more firmly and quickly, so the quantity is very small, usually between 0.2% and 1% of the weight of the liquid, depending on the texture you want. Too much agar will not only give an overly firm jelly, it will also affect the flavour.
- Add the agar agar to the cold liquid so it hydrates more easily.
- Bring the mixture to the boil – agar agar is only activated by boiling.
- Boil for a couple of minutes, but don’t overdo it: liquid evaporates and the jelly will end up too firm.
- Pour into moulds or containers straight away. Be careful – it sets very quickly, so you sometimes need to work fast.
- You can make jellies with alcohol, as long as you don’t add too much.
- Acidity weakens agar’s setting power, so an acidic jelly needs a little more agar.
- Unlike gelatin, agar agar is not affected by the enzymes in raw tropical fruits such as kiwi, pineapple and papaya – these enzymes break down proteins, and agar is a carbohydrate. That makes agar a good choice for jellies made with these fruits, as long as you account for their acidity.
What is agar agar used for?
Agar agar is used to make jellies and fluid gels. A fluid gel is made by blending a set agar jelly with an immersion blender or food processor until it becomes smooth and creamy – perfect for piping dots of intense fruit flavour onto plated desserts.
Can gelatin be replaced with agar agar?
It depends on the product and the texture you want. For jellies, agar agar can be a good option, as long as you accept a different texture. For mousses, it is not a good substitute, precisely because of how it is activated and how it sets. Since agar agar has to be boiled and starts setting while the mixture is still warm, you can’t fold whipped cream into it and get the light, airy mousse you get with gelatin. For a side-by-side comparison, read Gelatin vs Agar Agar.
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