straight to the sauce
Ho yau (literally 'oyster oil', better known as oyster sauce) is one of the most commonly used Cantonese condiments. A steaming plate of yau choi (blanched green vegetables served with a dollop of oyster sauce) is a ubiquitous dish at greasy-spoon diners, or cha chaan tengs.
Oyster cultivation and ho yau manufacture have been practised in the Pearl River Delta for centuries and were key industries in areas such as Deep Bay in the northwest New Territories.
Oysters need nutrient-rich waters to breed and in the days when local conditions were ideal, villagers had farming techniques down pat. Wooden or bamboo stakes were driven into the mud so the tiny oyster spawn could attach themselves. The stakes were moved according to changing tides.
Traditionally, oysters destined for sauce manufacture were washed and slowly simmered until well cooked, passed through a sieve to form a thick paste and seasoned with salt. The mixture was then allowed to age in earthenware pots. The resultant oily substance was bottled for sale. The sauce did not last long but modern pasteurisation techniques and chemical preservatives now ensure a lengthy shelf-life.
Cheap varieties owe much of their taste to mei jing (monosodium glutamate), that ever-present Chinese restaurant staple; better-quality ho yau is MSG-free. Some of the better-known local brands, such as Lee Kum Kee, started out in small towns along the West River in Guangdong and moved to Macau then Hong Kong.
Many small shops on Taipa and Coloane in Macau and in West River areas such as Sun Wui still manufacture their own sauces. Sadly, these long-established businesses are unlikely to survive much longer, whatever the heritage value of their products.
Worsening pollution in Hong Kong waters has led to a steady decline in local oyster production. Most of the fresh oysters sold in wet markets are produced on the cleaner, western side of the Pearl River or further up the coast towards Shantau. While an acute gastro-intestinal episode is unlikely if oysters are well cooked, heavy metals and other toxic concentrations are inevitable given the steadily increasing quantities of industrial effluent in Chinese coastal waters. Something to consider - or perhaps ignore - the next time you order that plate of steaming yau choi.