EL Vegetarian Mushroom Oyster Sauce 300ml Saus Tiram Vegetarian Vegetarian oyster sauce are prepared from mushrooms, mostly oyster mushrooms or shiitake mushrooms. This is because mushrooms, especially oyster mushrooms, have a high level of umami flavour similar to that of real oysters. Mushroom broth is a lighter caramel color compared to the darker molasses color of oyster sauce, but as a substitute, it is one of the better options. Mushrooms are just naturally so savory that you will get a nice balance of sweet, salty, and savory notes.