Oyster sauce is made of cooked oyster stock through concentration, dark brown in color, with a special fragrance, used as a condiment, many famous Cantonese dishes can not do without it, is one of the famous specialties of Guangdong. There are two kinds of oyster sauce: light oyster sauce and salty oyster sauce, the former made from oyster soup obtained by boiling oysters, and the latter made from salty soup juice after adding salt to cooked oysters.

Earth pot enrichment method of making boiled oysters is: the oyster soup juice with impurities precipitated by standing filtered through a sieve, injected into a large iron pot boiling, so that the water continues to evaporate, to be the liquid level drops and then add new soup continue to evaporate, this process is commonly known as "pumping soup". With the concentration of the pot oyster soup gradually become thicker, darker and darker color, nearly made of finished oyster sauce, the color was dark brown, liquid viscosity increased, the specific gravity of the finished product is generally in the 28 ~ 30, then made of oyster sauce.

At present, there are improvements, design of an atmospheric pressure and vacuum concentrator, and use it to refine oyster sauce has been successful, thus enabling the production of oyster products to achieve the main process of semi-mechanized production.