Only 1% of Japan's soy sauce is made through a centuries-old method

• Naturally fermented soy sauce used to be the norm in Japan for centuries. 
• When industrialization took over, the country's wooden barrels were replaced with steel ones. 
• Now, Yasuo Yamamoto is one of the last brewers in the country still building barrels and making traditional soy sauce.

It can take four years to make one batch of barrel-aged soy sauce. The natural fermentation process was the norm in Japan for centuries, but when industrialization swept the nation, almost all the country's wooden barrels were replaced with steel ones. Yasuo Yamamoto is on a mission to revive barrel-making and preserve the authentic version of Japan's staple seasoning.