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What are the roots of konjac?
The Indochinese Peninsula, Origin of the Materials
Konjac is a processed food made from the “konjac potato” (also called the “konjac bulb”) of the arum family. It is said that the origin of konjac potatoes is the Indochinese peninsula where they are nicknamed “elephant’s feet” for their shape.

Even now there are many different types of konjac potatoes growing wild in Southeast Asia. It is said that there are about 130 varieties, most of which are of a different kind than Japanese konjac potatoes and don’t contain the konjac mannan dietary fiber. This means that they are unsuitable for making konjac as they will not firm up even when processed. Perhaps for this reason konjac potatoes are only grown for food in limited areas of Japan and China, with only Japan having a well established konjac growing industry. It is thought that konjac was introduced from China in about the 6th century along with Buddhism, but no one can say for sure.

The lifespan of a konjac potato is around 4~5 years. After 3 years it does not get any bigger, but sprouts a flower, reproduces and dies.

The dark reddish-purple flower resembles the skunk cabbage of the same arum family. The leaf characteristically comes up from the bottom of the ground in one piece. When the flower opens, it releases a strong odor.

What kind of potato is a konjac potato?
3 Years to Your Table
Konjac potatoes, like regular potatoes, are grown from seed potatoes. However, unlike regular potatoes konjac potatoes take 2~3 years to mature.

First, the seed potatoes are planted in the spring and the new potato begins to sprout. From there the rhizome grows and in the fall you have a “baby” potato called a “kigo”. This kigo is then harvested and replanted in the spring for the 1st year. Then it is harvested again in the fall for the 2nd year. Then it’s replanted again the following spring and harvested in the fall for a 3rd year.

From the kigo stage to the 1st year the konjac potato will grow from 5~10 times its size. And from the 2nd year, it will grow another 5~8 times in size. By the third year it’s quite big, perhaps measuring about 30cm in diameter. After the 3rd year the potato is ready to be made into konjac.
However, because konjac potatoes are weak to low temperatures and rot easily they are a difficult crop to protect between harvests.
What kinds of konjac potatoes are there?
Better Quality with Cultivar Improvement
Formerly, in Japan “zairai” and “bicchū” varieties were grown. However, since these were very similar selective breeding was difficult. In the Taishō era (1912~1926) the “shina” cultivar was introduced from China resulting in success in breeding plants that were easier to grow.

As a result improved varieties such as “harunakuro” (in 1966) and “akagiōdama” (in 1970) were developed. Currently these two varieties account for more that 90% of all konjac production. Also, in 1997 the productive and easy to grow “myōgiyutaka” cultivar was introduced.
How are konjac potatoes grown?
Konjac Potatoes, “Un-dama”
Konjac potatoes have been grown for a very long time, but surprisingly a stable method of cultivation was not developed until around 1955. Since konjac plants are very delicate, even easily becoming diseased by injury to the leaves, they can’t be grown well in areas that are drought-prone, poorly drained or that have strong sunshine or winds. Through many years of experience and leaving things to chance or luck (“un”), farmers came to call this crop “un-dama” or “luck-bulbs”.
Since konjac potatoes need an average yearly temperature of about 13°C, despite being able to be grown in colder regions, growing them to a big size is difficult. So the northerly limit of outdoor cultivation is generally around Miyagi or Yamagata. In the past regular farmers would grow them for family use, but since emphasis has been placed on production quantity, more have been being produced in the northern Kantō region such as in Gunma, Tochigi, Saitama, etc.

View of a konjac potato field
Dryness and the damage from rapid temperature change are prevented by putting straw on the soil.
Since this makes it more difficult for weeds to grow it can also prevent disease and keep insects away.
Delicate Even After Harvesting
Temperature control is necessary for harvested konjac potatoes that will become seed potatoes. After drying the potatoes in the field for a half day, they are then dried some more in a shady, well ventilated location. During the winter they are individually wrapped in newspaper and placed in a well ventilated container in a location where the lowest temperature does not drop below 13°C.
Konjac Mannan Detoxification
Since long ago, konjac has been called the “stomach broom” and has been said to clear out dirt or sand from the digestive system. In other words, by eating konjac, rich in dietary fiber, you can clean out your body. Recently this old adage has been supported by various experiments. For instance, dioxin is well known as an environmental pollutant and especially for its deleterious effects on the development of infants and fetuses. According to studies done in rats, when 10% of the dietary fiber cellulose and rice bran fiber were added to their food, the amount of dioxin stored in their livers was reduced by 75~84% and the excrement of the rats that were given the fiber supplement contained 2.5 times more dioxin compared to that of the rats who were given normal food. This shows that dietary fiber adsorbs the dioxin circulating between the small intestine and the liver and passes it out of the body along with excrement.
What kind of benefits does konjac have?
The glucomannan contained in konjac is dietary fiber.

Dietary fiber, including glucomannan, a principle component of konjac, has recently been referred to as the sixth big nutrient along with the other already well known categories of protein, fat, carbohydrates, vitamins and minerals. Even though dietary fiber has not been considered as a nutrient because it is not digested or absorbed by the body, it has come to be referred to as a nutrient as the important benefits it provides by simply passing through the body have become clear.

It is said to be good for the prevention of colorectal cancer.
Though normal food is digested and absorbed in the stomach and small intestine dietary fiber goes straight to the large intestine without being digested or absorbed. There, it works to change the environment of the intestines. In today’s food culture we are always taking in food additives and other harmful substances into our bodies. Because dietary fiber works within the body to block the absorption of these harmful substances it is said to be effective at preventing colorectal cancer. This may be why it is often said that konjac is good for cleaning out the body.
It is said to relieve constipation.
One of the qualities of dietary fiber is that it absorbs water and swells up. Accordingly, when it reaches the large intestine its bulk has increased and it stimulates the movement of the bowels. This promotes bowel movement helps to relieve constipation. It’s a little different for everyone, but eating konjac definitely helps to improve bowel movement. Especially in the case of men, when they eat too much their stomach seems to get weak. (My personal experience)
It is said to be good for the prevention of diabetes and high blood pressure.
Diabetes is a disease where the blood glucose balancing hormone insulin is lacking or ineffective, causing a rise in blood sugar. Dietary fiber is said to have the effect of increasing insulin and repressing rises in blood sugar. It is also recognized as having the effect of returning back to normal the blood condition of those with high cholesterol or triglycerides, likely having the effect of preventing high blood pressure.
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