Agar, or agar agar, is a gelling agent extracted from red algae. It is commonly used to stabilize foams and to thicken or gel liquids. It is relatively easy to work with and a good starting point for modernist cooking.
Where to Buy Agar Agar
You can buy agar agar several places. We highly recommend ModernistPantry.com, they have great service and are really good to work with (because of this, we do have an affiliate relationship with them). You can also find it at WillPowder and get larger quantities at ForTheGourmet.com.
How Much Agar to Use
The firmness of an agar gel is determined by the amount of agar used to create the gel. The more agar that is used, the firmer the gel will be. Typically 0.2% agar is used for soft gels increasing up to 3.0% for firmer gels.
Fluid gels are usually made out of gels with a 0.5% to 2.0% ratio. Once again, the more agar used in the original gel results in a thicker fluid gel.
Agar foams use 0.3% to 1.0% for light foams and 1.0% to 2.0% for denser foams.
Agar Dispersion and Hydration
In order for agar to be used effectively it has to be properly dispersed and hydrated.
In order for agar to hydrate properly it has to be brought to a boil for 3 to 5 minutes. It also does not hydrate well in acidic liquids. If you are going to gel an acidic liquid, first hydrate the agar in a neutral liquid and then add it to the acidic liquid.
How to Create an Agar Gel
Creating a gel with agar results in a brittle gel. The firmness of the gel will depend on how much agar is used. You can make the gel more elastic by adding locust bean gum or gelatin to the flavored liquid when the agar is added.
Making an agar gel takes just a few steps. First, disperse the agar in the flavored liquid you want to gel using a whisk or blender. Then bring the liquid to a boil for 3 to 5 minutes. Pour the liquid into molds and let it set at room temperature.
The gel will set at 40-45°C / 104-113°F and remain a gel as long as it stays below 80°C / 175°F. Agar gels will usually range from 0.2% agar in a very soft gel to 3.0% agar in very firm gels. If you are making the gel more elastic you can replace from 5% to 15% of the agar with locust bean gum. If you are using gelatin, it should be added at about the same weight as the agar.
How to Create an Agar Fluid Gel
Fluid gels19 are substances that behave like a gel when at rest and like a liquid when force is applied. Ketchup is probably the best know example of a fluid gel, as anyone that has struggled to get it out of the bottle, only to have it flood their hamburger, can attest.
Once you understand how agar gels work it is very easy to create fluid agar gels. The simplest way to create an agar fluid gel is to create a normal agar gel and let it set. Then puree the gel until smooth using an immersion blender or standing blender. You can thicken the fluid gel by adding some xanthan gum or thin it out by adding water or another liquid.
In general a ratio of 0.5% to 2.0% will be used to create the gels used for fluid gels.
How to Create an Agar Foam
Agar foams are made from agar fluid gels that are dispensed from a whipping siphon. These foams are thick, fine foams that are very dense. Because agar holds its shape under higher temperatures these foams can be served hot or cold.
For agar foams the more agar you use the denser the resulting foam will be. For light foams, a ratio of 0.3% to 1% works well. For denser foams 1% to 2% is recommended. You can also add gelatin, locust bean gum, or xanthan gum to change the density of the foam.
Interested in more information like this?
Modernist Cooking Made Easy: Getting Started covers many of the popular modernist techniques such as gelling, spherification, and foams. It also explores modernist ingredients like agar, sodium alginate, tapioca maltodextrin, and xanthan gum.
It is all presented in an easy to understand format along with more than 80 recipes and photographs.
I might be biased but I think it's the best way to learn about modernist cooking!
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