Traditionally made Tamari such as Mitoku's Yaemon, which is long aged in wood, contains no wheat, and is made with a very high percentage of whole soybeans, accounts for a very small part of the world's tamari production. According to Japanese Agriculture Standards (JAS), even a product made with 20% wheat can be called tamari.
Besides adding wheat modern tamari manufacturers make a much more dilute product than Mitoku's Yaemon tamari. Authentic Go-Bu tamari, such as Yaemon's, is made from 10 parts soybeans and 5 parts water. Therefore Go-bu tamari moromi is very thick and difficult to press and extract out the rich, concentrated tamari.
In contrast, to save time and money, modern tamari makers use a ratio of 10 parts soybeans to 10 parts water. What's more, most tamari is made by the rapid commercial process using hexane-defatted soybeans, fermented at high temperatures for three to six months, and often bottled with additives. An even lower grade product, called synthetic tamari, is often sold in supermarkets. This product is not even fermented, but is a mixture of hydrolyzed soy protein, color additives, and flavoring agents.