Excavations in the western part of Obama revealed the remains of the Okozu Salt Production Site, an ancient government-run facility that drew seawater from the bay to make salt using a combination of concentrating, boiling, and baking. Fragments of earthenware and locations of several stone-paved furnaces were discovered at the site, which is estimated to have been in operation between around fifth and eighth centuries. The area is designated a National Historic Site.
Japan does not have rock salt deposits and is too humid to produce sea salt by evaporation alone, so for centuries the process involved using furnaces to boil seawater down to crystallized salt. First, seawater was poured over dried seaweed or seaweed ash to increase salt concentration. Then it was boiled down in large earthenware pots to crystallize the salt. Finally, the resulting coarse salt was baked in clay pots, which separated out bitter compounds and shaped the final product for convenient preservation and transportation.
In the eighth century, the Wakasa region was an important salt producer and sent salt as tax payments to Heijokyo (present-day Nara), the capital at the time. The comparatively well-preserved Okozu site is one of approximately 60 ancient salt manufacturing locations that have been confirmed in Wakasa. Multiple wooden tablets that were used as shipping tags for Wakasa salt were discovered during excavations of Heijokyo.
