Ako’s salt is indispensable for making soy sauce in Harima. The area has prospered as a salt-producing region since ancient times. During the Edo period, in the Irihama saltpans, their salt-making method was perfected, and the technique was widely spread throughout the Seto Inland region. The saltpans in the east and west produced salt of different quality; common salt was transported to the Kanto and northern areas, while high-quality salt was transported to the Kinki region, mainly the Kansai region, where people preferred a lighter taste. It was distributed to various places by flatboats and salt cargo vessels.

In Tatsuno, in addition to brewing soy sauce, Ako’s salt became an important raw material to produce somen noodles.

As a result of excavation, much salt glaze pottery from the late Yayoi period was unearthed, and the remains of a saltpan from the Heian period were found for the first time in Japan. Later, people began to migrate to the area in the Middle Ages, and roads leading to Himeji in the east and Bizen in the west were constructed. In the Edo period, the Ikeda family actively promoted the salt manufacturing business, which entered Harima later by the Asano family. The profits from the saltpans further developed the town. After the Meiji Restoration, unions were formed on the east and west shores. The government put a monopoly system to protect against imported salt, foster the domestic salt industry, and secure financial income.

Although the production method has changed from the sloping salt-terrain approach to the ion-exchange membrane electrodialysis method, Ako’s salt is still produced today.

In Ako, salt production methods have changed over the years, starting with salt glaze pottery using earthenware vessels. Next was a production method using the ebb and flow of the seawater to reduce the labor required for fetching water, then the more streamlined old-fashioned Irihama method, and later, the large-scale channeled salt-terrace process utilizing dikes. For the Irihama saltpans, Ako met all the necessary conditions, such as the number of sunny days and hours per year, topography, and a tidal range of at least one meter. When this production method was introduced in the Edo period, the area along the Seto Inland Sea was responsible for more than 80% of the nation’s salt production and was called “Jyushu Enden.”

The rivers flowing in the vicinity played a vital role in the work required for salt production. When manufacturing salt, a tremendous amount of firewood was used to boil down the concentrated salt water (brine), which was brought in from the upper reaches of the Chikusa River by flatboats. A rare lighthouse can be seen in the Une area as a remnant of these times. The salt produced in the Higashihama and Nishihama saltpans was transported to salt warehouses by flatboats that plied the waterways lining the fields. The salt warehouses and channels of the Nishihama saltpans remain today.

Ako’s salt sales were divided: offshore sales to other countries by salt cargo vessels and hawking within the territory’s interior. The common salt, made by roasting salt in a stone kiln in the east and west saltpans, went to eastern Japan, including Edo and Kyushu. The small, white, elegantly flavored high-quality salt from the Nishihama saltpans was sent to the Kinki region, mainly Osaka. Salt seems to have been spread further in Ako’s territory by furiuri, salespeople who shouldered a carrying pole containing goods and by flatboats. Thus, the salt that reached Tatsuno became the raw material to produce soy sauce, with excellent quality.