"True" oyster sauce of good quality should be made by condensing oyster extracts, the white broth produced by boiling oysters in water.
This opaque broth, similar to the colour of clam juice found in supermarkets, is then reduced until a desired viscosity has been reached and the liquid has caramelized to a brown colour.
No other additives, not even salt, should be added to the sauce, since the oysters should provide all the savoury flavour.
However, this method is prohibitively expensive.

Many modern oyster sauces are thickened with cornstarch, flavoured with oyster essence or extract and darkened with caramel.
"True" oyster sauce of good quality should be made by condensing oyster extracts, the white broth produced by boiling oysters in water. This opaque broth, similar to the colour of clam juice found in supermarkets, is then reduced until a desired viscosity has been reached and the liquid has caramelized to a brown colour. No other additives, not even salt, should be added to the sauce, since the oysters should provide all the savoury flavour. However, this method is prohibitively expensive.
Many modern oyster sauces are thickened with cornstarch, flavoured with oyster essence or extract and darkened with caramel.
Oyster sauce