Sponges: How Do They Work?

They wash your dishes, your car, even your back. Sponges are a ubiquitous tool of the modern world—and have been since the earliest days of mediterranean culture—but how much do you really know about the absorbent little helper riding your kitchen sink's rim?

Until just recently, sponges the animal and sponges the domestic tool were one and the same. These ancient plant-like animals first appeared in the world's oceans some 700 million years ago and are among the most basic forms of macroscopic aquatic life. They possess no specialized organs—no lungs, gut, or brain—and both feed and breathe by filtering particles and oxygen from seawater pumped through its body cavities.

Composed of a material called spongin, sea sponges have been harvested and dried for human industry for thousands of years. Specifically, two species—Spongia oficinalis and Hippospongia canaliculata, which lack the hard calcium carbonate layer of other sponges, have been collected by free divers throughout the mediterranean since the age of the Greeks.

Throughout history, sea sponges have been used for a myriad of applications—from padding Roman Centurion helmets to early canteens to municipal water filters—even contraceptives. They were used so extensively that we nearly wiped out these species through rampant overfishing until the start of the 20th century. 

Demand was so high because sponges are fantastic at what they do. Since the animals are really about 66 percent empty space, they can intake enormous amounts of water. And, thanks to their spongin composition, which swells to prevent water from seeping back out of the sponge's pores until forcibly squeezed, this material is ideal for trapping and holding liquids.

It wasn't until the 1940's that sea sponges caught a break from being caught by divers when researchers at Du Pont invented the world's first artificial sponge. Created from a mixture of cellulose, sodium sulphate, and hemp fiber, this material proved more durable and less costly to produce than natural slow-growing sea sponges, which is why it's difficult to find a natural sponge on store shelves these days. Du Pont held onto this patent, and sole rights for producing artificial sponges, until 1952.

Today, many sponges are still made from Du Pont's cellulose process though many are also generated from foamed or spun plastic polymers as well. Cellulose is perfect for artificial sponges because, like spongin, it absorbs water rather than break down in it. The fiber's structural rigidity also increases the sponge's strength and durability. The addition of artificial abrasive pads or nylon-mesh sheaths (a la Dobie Pads) also assist in removing stuck on food bits.

Artificial sponges are created by combining the cellulose and hemp fibers with sodium sulphate crystals in a large rolling drum until they're well-mixed, then baking them iu large rectangular forms. During the heating process, the sulphate crystals break down to form intricate hole and pore structures that provide the sponge's absorbency. It is then cut to size, bleached, rinsed with water, then packaged. This rinsing and packaging step is why brand-new sponges always seem a little damp when you first pull them out of the shrink wrap.

Unfortunately, a sponge's knack for holding onto liquids also make them ideal breeding grounds for bacteria that cause foodborne illnesses. According to the USDA, a sponge that is left unattended for two to three days after cleaning up a kitchen spill can house bacterial and fungal colonies numbering in the millions. That includes E coli and a host of other potentially deadly strains.

Luckily, you can easily clean and disinfect your sponge by either washing it with a load of white laundry (don't skimp on that bleach) or filling it with water and microwaving for two minutes. Just don't overdo your cook time; if the sponge dries out completely it can catch fire in the microwave—leaving you with an even bigger mess to clean up. [MadeHow - eHow 1, 2 - Wiki]

Image: Bozena Fulawka

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