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Agar, the plain red seaweed doesn’t appear to be an important plant, at first glance. But it has made vast contributions to bacteriological science. A member of a large group of seaweeds, some quite beautiful, the red pigment is a camouflage of its green chlorophyll. Because it is an inhabitant of the deep, dark waters, it’s more colorful than seaweeds that exist near the light in shallow tidal areas.

Agar, Gelidium cartilegineum, is a small, reddish brown, cylindrical plant that reaches only 6 inches in height. Despite its diminutive size, agar’s bushy stems and branches are tough. The cells of this plant contain an odorless, tasteless, colorless, and transparent substance called agar. When boiled in plain water or in water to which sulfuric acid has been added, this seaweed yields a gelatinous substance that is called agar.

Because agar is indigestible by practically all bacteria, it is an excellent base on which to grow laboratory bacterial cultures. The bacteria consume the substance in which they are grown but not the agar. German bacteriologist Robert Koch discovered this in the 1880’s.
And because agar is also indigestible by humans, it is now a common ingredient of packaged diet foods. Agar fills the stomach without adding calories!

In Japan, agar is put into sauces, soups, jellies, and desserts. In the West, it is used as a gelling and stabilizing agent by meat and fish canneries, and in baked goods, dairy products, and candies as well.

An extremely useful medicinal asset of agar is that it is hydrophilic, which means it absorbs water. So it is effective as a bulk laxative. It soaks up the water in the intestines and increases the bulk of waste material. And because of its water-absorbent capacity, agar is also used by dentists, and is manufactured into emulsions, lubricants, suppositories, and cosmetic gels.