Underground Water Brings Out the Umami of Izu Natto

Apr 27, 2025 | News On Japan

SHIZUOKA, Apr 27, 2025 (News On Japan) - Soybeans steamed to a tender finish in a pressure cooker — this is the foundation of 'Izu Natto,' made from locally grown soybeans and the water of Izu.

Marusa Foods, founded 72 years ago as of 2025, is the only natto manufacturer in the Izu region. The company has earned national recognition, winning awards three times at a competition where about 100 natto makers from across Japan compete. Its signature product, the "Medium-Sized Soybean Natto," is highly praised for its quality.

Each soybean in the natto is firm, and the rich umami spreads across the palate with every bite, creating a deeply satisfying flavor that pairs well with rice. Kyoaki Saito, the third-generation head of Marusa Foods, explains that the texture is intentionally firm, allowing the taste of the soybeans to deepen with each chew. Saito inherited the business from his grandfather and father, maintaining the company’s commitment to carefully selected ingredients. For their main product, they use a variety of soybeans known as "Fukuyutaka," harvested within Shizuoka Prefecture.

Another key element in their production is water. Water is vital in many steps, including washing the soybeans and preparing the seasoning, and Saito emphasizes that both soybeans and water are the most important factors in making good natto. The underground water flowing from the rich natural environment of Izu, including Mount Amagi, plays an essential role. High-quality water helps tighten the flavor of the soybeans, creating a deeper, more refined taste. Seeking such ideal water, Saito’s father, Ryuichi, relocated the factory to its current site.

Care is taken from the very beginning of the process, as fermentation is sensitive to the cleanliness of the soybeans. After a meticulous washing, the soybeans are soaked overnight in underground water. They are then steamed slowly for about an hour in large kettles. Once softened, they are sprayed with water mixed with natto bacteria, quickly packed, and allowed to ferment overnight in a specialized room.

On a typical day, Marusa Foods produces between 1000 and 2000 packs of natto, but during busy periods, production can rise to 4000 to 5000 packs. Saito said he wants to continue creating distinctive natto by using carefully selected beans, offering a variety of flavors to customers. Marusa Foods also provides locally made natto for school lunches in the eastern part of Shizuoka Prefecture, and Saito hopes their products will inspire a new generation of children to develop a love for natto.

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