In chinese cuisine, dark soy sauce (chinese: 老抽; pinyin: lăo chōu) is a dark-coloured soy sauce used mainly for adding colour and flavour to dishes. it is richer, slightly thicker, and less salty than other types of soy sauce. as the chinese name lăo chōu (lit. 'old extract') suggests, it is also aged longer. it is often sweetened by adding molasses or other sweetening agents. dark soy sauce is often used in stews, stir-fries, and sauces. it is used in dishes requiring colours, such as red cooked dishes.

Source: Wikipedia