On the coast of Onjuku, in Chiba Prefecture, lies Iwase Shuzo, a brewery that has been run by the same family since its founding in 1723. Its location near the Pacific Ocean is not only picturesque but also determines the character of its sake: the brewing water is drawn from aquifers rich in fossilized shells, resulting in an exceptionally high mineral content.

With a hardness of approximately 240 ppm, the water is among the hardest in Japan. These minerals—particularly calcium and magnesium—stimulate fermentation and give the sake a distinct, vibrant profile. The result is a style distinguished by freshness, depth, and a subtle tension in the flavor. These qualities make Iwase's sake particularly well-suited for pairing with dishes such as shellfish, grilled fish, or even cheeses.

In 1947, the flagship brand IWANOI was awarded "Japan's Best Sake" at the national sake competition. Since then, the brand has built a loyal following among enthusiasts and professionals, and is regularly praised for its balance between tradition and expression.

Iwase Shuzo is a brewery that literally puts its local heritage in the bottle. Using local water, Chiba rice, and age-old techniques, they create a sake that reflects not only craftsmanship but also the unique geology of Japan's coastline.