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A Little Something About Agar

June 19th, 2009

The use of seaweed as food has been traced back to the fourth century in Japan and the sixth century in China. Today those two countries and the Republic of Korea are the largest consumers of seaweed as food.

China is the largest producer of edible seaweeds, harvesting about 5 million wet tons annually. The greater part of this is for kombu, produced from hundreds of hectares of the brown seaweed, Laminaria japonica, that is grown on suspended ropes in the ocean. The Republic of Korea grows about 800,000 wet tons of three different species, and about 50 percent of this is for wakame, produced from a different brown seaweed.

Various red and brown seaweeds are used to produce three hydrocolloids: agar, alginate and carrageenan. A hydrocolloid is a non-crystalline substance with very large molecules and which dissolves in water to give a thickened (viscous) solution. Alginate, agar and carrageenan are water-soluble carbohydrates that are used to thicken (increase the viscosity of) aqueous solutions, to form gels (jellies) of varying degrees of firmness, to form water-soluble films, and to stabilize some products, such as ice cream (they inhibit the formation of large ice crystals so that the ice cream can retain a smooth texture). Agar-Agar is one of the most ancient stabilizers used in food.

The best quality agar is extracted from species of the red algal genera Pterocladia, Pterocladiella and Gelidium, and is harvested around the world. Agars of lesser quality are extracted from Gracilaria and Hypnea species. Agar quality is seasonal in Pterocladiella species; low in the colder months and high in the warmer months.

In several countries, such as Chile and Indonesia, most of the harvest is from attached weed that is picked by hand either at low tide or by snorkeling in shallow waters.

More than 50% of food grade Gracilaria is extracted from Gracilaria gracilis and Gracilaria chilensis. Gracilaria species were once considered unsuitable for agar production because the quality of the agar was poor (gel strength too low). In the ‘50s, it was found that pre-treatment of the seaweed with alkali before extraction lowered the yield but gave a good quality agar. This allowed expansion of the agar industry, and led to the harvesting of a variety of wild species of Gracilaria in countries such as Argentina, Chile, Indonesia and Namibia.

Processing Flakes/Powder

Gelidium (which is the variety that we carry on EDTV), is simply washed to remove sand, salts, shells and other foreign matter and is then placed in tanks for extraction with hot water. The agar dissolves in the water and the mixture is filtered to remove the residual seaweed. The hot filtrate is cooled and forms a gel (jelly), which contains about 1 percent agar. The gel is broken into pieces, and sometimes washed to remove soluble salts. Then the water is removed from the gel, either by a freeze-thaw process or by squeezing it out using pressure. After this treatment, the remaining water is removed by drying in a hot-air oven. The product is then milled to a suitable and uniform particle size. This is the least processed of the agar varieties.

Gracilaria is also washed, but it must be treated with alkali before extraction; this alkaline pre-treatment causes a chemical change in the agar from Gracilaria, resulting in an agar with increased gel strength. Without this alkaline pre-treatment, most Gracilaria species yield an agar with a gel strength that is too low for commercial use. For the alkali treatment, the seaweed is heated in 2-5 percent sodium hydroxide at 85-90°C for 1 hour; the strength of the alkali varies with the species and is determined by testing on a small scale. After removal of the alkali, the seaweed is washed with water, and sometimes with very weak acid to neutralize any residual alkali.

Agar for use in food is sold in two forms: strip agar and agar powder. The powder is produced by the method previously described above. Agar strip, sometimes called natural agar, is produced on a small scale in the Republic of Korea, Japan, and China.

The use of agar is dependent on the unique properties of its ability to form gels. Agar dissolves in boiling water and when cooled it forms a gel between 32° and 43°C, depending on the seaweed source of the agar. In contrast to gelatin gels, that melt around 37°C, agar gels do not melt until heated to 85°C or higher. In food applications, this means there is no requirement to keep them refrigerated in hot climates. At the same time, they have a mouth feel different from gelatin since they do not melt or dissolve in the mouth, as gelatin does. This large difference between the temperature at which a gel is formed and the temperature at which it melts is unusual, and unique to agar. Many of its applications take advantage of this difference.

About 90 percent of the agar produced is for food applications, the remaining 10 percent being for bacteriological and other biotechnology uses. Agar has been classified as GRAS (Generally Recognized As Safe) by the United States of America Food and Drug Administration, which has set maximum usage levels depending on the application. In the baked goods industry, the ability of agar gels to withstand high temperatures means agar can be used as a stabilizer and thickener in pie fillings, icings and meringues. Cakes, buns, etc., are often pre-packed in various kinds of modern wrapping materials and often stick to them, especially in hot weather; by reducing the quantity of water and adding some agar, a more stable, smoother, non-stick icing is obtained.

The use of agar is dependent on the unique properties of its ability to form gels. Agar dissolves in boiling water and when cooled it forms a gel between 32° and 43°C, depending on the seaweed source of the agar. In general, combining agar into our vegan and vegetarian diets, is tantamount in stabilizing ice creams, sherbets, jellies, meringues, marshmallows and the list goes on and on.

Everyday Dish carries the Geledium variety of agar. It is manufactured in Spain. You can find it on our Market page in YaYa’s Pantry.