Saltpeter Production in Gokayama

For over 300 years during Kaga domain rule, Gokayama produced saltpeter in secret, fueling one of feudal Japan's most strategically sensitive industries. The process was carried out in pits under the irori fireplaces of gassho-zukuri farmhouses, where straw, soil, and silkworm excrement fermented for five years before calcium nitrate could be extracted. The isolated mountain terrain made Gokayama ideal for keeping the operation hidden even from the shogunate. After cheap Chilean imports collapsed the market in the Meiji era, production ended. The Saltpeter Museum in Suganuma village displays tools and materials from the process inside a restored gassho-zukuri house.