Oyster sauce is a viscous sauce prepared from oysters and brine, often with chemical preservatives added. It is much used in Chinese cooking. The sauce is often used as a topping for steamed vegetables such as kailan and in stir-fried food.
Vegetarian oyster sauce prepared from mushrooms, is also popular and generally cheaper.
Making Oyster Sauce
A 'True' oyster sauce of good quality should be made by condensing oyster extracts (which is made by cooking oysters in water, where the aqueous mixture is then cooked until a desired viscosity has been reached ) alone and no other additives except salt. The sauce should be aromatic with great flavour. Sadly, however, this would be costly and only a handful of manufacturers are willing to do so. Quite a number of oyster sauces are actually diluted solution of concentrated ones.
The use of Oyster Sauce
Oyster sauce is capable of enhancing flavour of other food. A tablespoon of it makes plain Chinese noodles no more oridinary.
Typical oyster sauce has MSG added, but in recent years MSG-free varieties can also be found. The differences (in terms of taste) between MSG and non-MSG variants maybe indistinguishable.