There are two types of tamari: genuine tamari and shoyu tamari.
Genuine tamari is made from soybeans, sea salt, water, and koji (a
culture of lactic acid producing microorganisms). The ingredients are
left to ferment in large wooden casks for 2-3 years before filtered
and pasteurised.
Shoyu tamari also contains wheat as well as
soybeans, water, sea salt, and koji, and the fermenting period is
usually only 2 years. Compared to genuine tamari, shoyu tamari tastes
slightly sweeter. Unfortunately, some people intolerant to wheat and
gluten react to shoyu tamari because of the trace amounts of gluten
sometimes present. This problem does not occur with genuine tamari.
There is also soy sauce, which is Chinese, whereas tamari is Japanese. Soy sauce contains the same ingredients as shoyu tamari and often small amounts of sugar or syrup as well. Thus, it is less suitable for allergics or people with dysbiosis.