Oyster sauce 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. Vegetarian oyster sauce prepared from mushrooms, often oyster mushrooms or shiitake mushrooms, is also popular and generally lower in price. It may contain more taste enhancers if less mushroom extract is used to reduce costs. Most of the oyster sauces available on the market contain added monosodium glutamate (MSG). In recent years MSG-free varieties can also be found. The taste
Flat morphism is flat. Easy examples of this are elliptic fibrations, smooth morphisms, and morphisms to stratified varieties which satisfy miracle flatness on each of the strata. A simple non-example of a flat morphism is formula_8 This is because if we compute formula_9 we have to take a flat resolution of , and tensor the resolution with , we find that showing that the morphism cannot be flat. Another non-example of a flat morphism is a blowup since a flat morphism necessarily has equi-dimensional fibers. Let be a morphism of schemes. For a morphism , let and . "f" is flat if