Anyone living in or even visiting Japan will likely have come across a certain ghastly, grey, gelatinous substance.

In most cases, local people are at a loss to answer the questions that inevitably follow. An enigma of the food world, konnyaku is either loved or detested. There is no in-between.

This mysterious food is derived from the corm (the bulbous underground stem) of the konjac plant, which goes by such intriguing monikers as “devil’s tongue,” “voodoo lily,” “elephant yam” and “snake palm.” Hints, perhaps, to the nature of the consequent product.

Grown, processed and consumed primarily in Japan since the sixth century (originally for medicinal purposes), this food product is commonly referred to as a kind of yam or potato, although it actually bears no relation to the edible tuber family.

To make it, the pulp of the mature konjac corm is dried and processed to form a flour of sorts, which is then mixed with calcium hydroxide and water, giving rise to its rubbery viscosity. The substance is then boiled and cooled into a solid block. Konnyaku without any additives is a pale white color, but often hijiki seaweed is added to lend a slight hue and flavor to what is essentially a colorless, flavorless product.

Over 90 percent of konnyaku is water, with what remains being glucomannan, a soluble fiber and emulsifier, and it is this component that has led to the product being hailed as the ultimate diet food by its supporters.

Konnyaku contains virtually zero calories, no sugar, fat, protein, gluten or carbohydrates. What it does have is high quantities of a fiber that the body cannot easily digest. For this reason, Japanese people often refer to konnyaku as a “broom for the stomach” — it sweeps through your small intestine, so to speak, performing a thorough clean out.

What konnyaku lacks in flavor and substance it makes up for in texture. More rubbery and gelatinous than any edible substance known to man, you will actually burn more calories chewing it than you’ll get from digesting it. It is most commonly found in the Japanese staple, oden, a winter soy-flavored dashi broth with various floating parts such as boiled eggs, processed fishcakes and daikon radish. Konnyaku sometimes makes a double appearance: once in the block form, and again as shirataki, a noodle-like manifestation.

To entice the youngsters, konnyaku is made into a fruit jelly snack served in single-shot plastic cups. These are sold all over Asia and their popularity also spread to North America and Europe. Until, that is, it became the cause of death by choking and suffocation in 17 reported cases since 1995, leading the U.S. Food and Drug Administration to issue warnings in 2001. The product was later recalled in the United States and Canada.

The European Union responded more fiercely, implementing an outright ban on the sale of the jelly snack. Unlike most gelatin products, konnyaku does not dissolve in the mouth, nor with pressure from air or the tongue. Rather, it requires intense chewing in order to be safely swallowed. If sucked with enough force, such jelly shots can easily become lodged in the throat, causing a potentially fatal choking hazard. As a result, the size of the product has now been increased, and it now comes with a warning on the package.

As a potential health hazard that contains little to no dietary value, can konnyaku even be classified as a food? According to the title of a recipe book published in Japan in 1846, “Konnyaku Hyakuchin,” there are one hundred culinary uses to which it can be put. I’ll let you be the judge of that.

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