Chinese style soy sauces are usually brewed for a few weeks with soybeans, salt, wheat and water. After brewing, caramel colouring may be added to give the sauce its distinctive dark colour. Chinese style soy sauces are often used for colour rather than flavour. ‘Light’ and ‘dark’ refer to the colour of the sauce, not how salty it is. In fact, a Chinese style light soy sauce can taste saltier than a dark one!
Japanese style soy sauces, also known as shoyu, are usually brewed for months rather than weeks, and may be aged for even longer to develop the flavour. Generally, Japanese soy sauces are brewed with less salt than their Chinese style counterparts. Roasted wheat and a mixture of yeast and fungal cultures – also known as koji – are key ingredients in Japanese soy sauce. Colourings are rarely, if ever, used.