Sunday, September 26, 2010

Hydrocolloids- Agar

Agar is another example of a phycocolloid (a colloid extracted from seaweed). It was actually discovered years before the other 2 phycocolloids (carrageenan, and alginate). Agar is a very versatile gelling agent. It forms thermo-reversible gels that gel when cooled and melt upon reheating. When using agar it is good to know that even the smallest concentrations (.2%) can create a stable gel. When used as your sole gelling agent agar forms brittle gels with a very short texture. I have used agar for a variety of different applications in the pastry kitchen. One of the biggest uses that I have come across is "fluid gels". Basically a fluid gel is a gel that has been set and then reblended to form a "thickened" sauce or puree. Agar can also be used in conjuction with other hydrocolloids to form a wide range of textures. One of the most common synergies is the agar/ locust bean gum (LBG) concentration. By adding a small ammount of LBG to your recipe you can vastly change the outcome of the gel. The gel strength will be increased, and the texture of the resulting gel will become more elastic. This can provide a better mouthfeel when eating the gel. Agar gels also have the ability to become heat stable to a point. Gels made using agar can be held at temperatures up to ~80 C before remelting. This can be a desired property if your trying to make a "hot gel". Below is a basic fluid gel recipe using agar.

Fluid Gel
350 liquid
1.5 agar
.5 ascorbic acid
1.5 gelatin
tt sugar

Bloom gelatin in ice water
Sheer agar, ascorbic, and sugar into liquid
Bring the liquid to a boil while whisking
Simmer for 1 minute
Take off heat, and add bloomed gelatin
Poor out and leave to set
Vitaprep the gel smooth


  1. The gelatin and ascorbic acid are unnecessary. The agar will set first, and even if you leave it long enough to set the gelatin, you'll usually melt the gelatin when vita-prepping due to the heat. The ascorbic acid may be desirable for flavor, but that depends on what your base liquid and desired results are.

    Also, it's worth mentioning that agar has a more pronounced seaweed flavor than many other hydrocolloids, and shouldn't be used for any delicately-flavored bases. Instead use gelatin, gellan, etc.

  2. Also worth mentioning that this recipe, with .4% agar, creates a fairly loose fluid gel. For a tighter gel, use a higher percentage of agar, up to 1.2% or so.

  3. There is a reason why I mention "basic". Even though the recipe calls for .4% agar the added gelatin will prove to make the finished gel more viscous. Even though you will be using the vitaprep to sheer your gel, if you "melt" the gelatin the gelatin will help to reset the gel when properly cooled or icebathed. And the reason behind ascorbic is to season the gel, much like you would season with vinegar. Also worth mentioning that if you were to use 1.2% agar (in this recipe) I can assure you, that the product will be very unappetizing due to the fact that agar does have a "seaweedy" flavor. I never mentioned that agar is the ideal hydrocolloid to use when making fluid gels, I agree that there are a host of other alternatives that produce high quality gels.