Shoyu is made from cooked wheat and soya beans mixed with a fermenting culture and water. It is left to ferment for about 24 months in cedar casks, then pasteurized and bottled.
Tamari (traditionally wheat-free) is made from cooked soya beans, crushed into tiny balls. The balls are dusted with roasted barley flour and aspergillus culture, incubated for 48 hours, then mixed with water and sea salt and placed in cedar vats for 18 months.
The resulting mash of the beans is pressed, pasteurized and bottled.