Across the country, from Hokkaido to Okinawa, bacteria brought back by a Japanese scholar from a remote village in the former Soviet Union have been multiplying like crazy.

It has even reached the point where a voluntary group has formed with the aim of bringing it under control.

But these bacteria will not hurt the body — on the contrary, they are said to be good for one’s health.

The bacteria are a necessary ingredient to churn out what is being called “Caspian yogurt.” Though not available as a commercial product, the yogurt, which is more viscous than regular yogurt, has spread throughout the country with amazing speed via word of mouth.

“I was lucky to be able to get it through my friend at a cooking school last spring,” said Yuko Yamaguchi, 58, who works at an insurance company in the city of Hiroshima. “I think I’ve given it out to around 100 people already.”

Ikuko Maeda, a Yokohama housewife, obtained the yogurt from her daughter’s friend over the summer and said she eats it twice a day and makes about a half-liter every three days or so.

“It doesn’t have a sour taste and it’s easy to eat. And on top of that, it’s good for my stomach,” said Maeda, also 58. “Now my daughter, who’s heading to Seattle for studies, is even thinking of taking the yogurt with her to cultivate it.”

The yogurt’s popularity may have hit boom proportions recently, but it was actually two decades in the making.

Yukio Yamori, professor emeritus of pathology at Kyoto University, visited the Soviet Republic of Georgia in 1986 for his studies on longevity.

He had long wanted to visit Georgia to examine the diets of local people, because areas around the Caucasus Mountains were noted for having one of the highest life expectancies in the world.

The Georgian yogurt, called Matsoni, was brought back as a sample for his studies, as it was eaten in large amounts and prepared by almost every household.

Apart from analyzing its nutrients, Yamori one day decided to mix a small portion of the yogurt he had kept in a refrigerator with some milk at home.

“I was shocked at the strength of the bacteria contained in the yogurt. It was so easy to reproduce the original,” Yamori recalled.

Yamori, 65, also said he never expected the yogurt to become the rage it is now, because he was simply enjoying the nutritious food at home with his family.

“To be honest I can’t really tell and trace exactly how the yogurt has become widespread in the country,” Yamori said, adding that he is not the one who named it “Caspian.” Ironically, Georgia does not border the Caspian Sea to the east but the Black Sea to the west.

Yamori said as far as he is aware, his wife, who is also a doctor, gave it to a friend for a postoperative diet sometime in 1986 and later it was also shared by some doctors in their circle.

“Presumably, it was circulated by doctors at first because they move a lot around the country,” said Yamori, who currently heads the World Health Organization Collaborating Center for Research on Primary Prevention of Cardiovascular Diseases.

In any case, since then, strains of the calcium-rich food, which was dubbed Caspian yogurt by a health magazine, has traveled from one household to another, very often with a piece of paper containing the recipe as well as some historical background.

Some people welcome the health benefits of the yogurt, saying it is not only effective in regulating the functions of the intestines, a widely known benefit of yogurt products, but also in preventing various types of allergies and age-related disorders.

Others simply seem to enjoy the simple process of making the yogurt — just pour milk over the bacteria strain, and leave it at room temperature for a day.

But the yogurt’s popularity, and its unavailability in retail stores, has also prompted concerns about safety.

Backed by a recent string of favorable comments made about the yogurt in magazines and on TV shows that cover health topics, demand for the yogurt has skyrocketed, and an increasing number of people have started sharing its strains with people they do not know via avenues that include the Internet.

Companies meanwhile have not yet tried to capitalize on the Caspian yogurt explosion, viewing its ease of production at home as something not likely to turn a profit.

“I was deeply concerned about its safety.” Yamori said. “I thought it has reached a point that I must do something.”

Yamori decided to get help from a volunteer group in Kobe that was established in October to work for food safety, to distribute the original strains on a nonprofit basis to those wishing to obtain them.

The group launched the service on Nov. 1 by consigning the production and shipment of freeze-dried powder of the strains to Kobe-based food firm Fujicco Co.

“Our office has been flooded with calls from all over,” said Saburo Kawahara, 75, a volunteer with the group. “Can you believe it? We receive as many as 2,000 to 3,000 requests a day . . . we had only prepared a total of 3,000 packages in the beginning.”

As for Yamori, he hopes the Caspian yogurt craze, however long it lasts, may be a step toward pulling younger Japanese out of a “poverty in calcium,” referring to recent data showing that around 40 percent of young Japanese suffer broken bones before they graduate from high school.

He even hopes the yogurt could become a daily staple for Japanese, much like rice. “The taste of it is simple. You can mix it with many other things and eat it in many different ways.”

“Just as long as it’s safe, I’m very happy to see the spread of this yogurt,” Yamori said.

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