See How Soy Sauce is (Still) Made in Japan
Soy sauce has been around for thousands of years, and in the Japanese town of Yuasa it is still made using a 750-year-old process devised by a monk who brought secrets from China.
In Yuasa, soy sauce is created from a fermented mash of soybeans, wheat, salt, and water. The recipe for making it includes an extensive set of steps, including heating, filtering, pressing, aging, skimming, heating again, and eventually bottling. The fermentation process can take as long as 3.5 years (but no less than 18 months).