To make double brewed soy sauce, first a 'regular' batch is made using soybeans, wheat, salt, water & koji. They a second batch is brewed, except this time the salt and water are omitted and the first batch of soy sauce is used instead. This produces a soy sauce with a deeper, softer flavor and more viscous texture than regular soy sauce. It is also surprisingly less salty than regular soy sauce.
Made in Japan.