When considered as carriers of flavor, sauces form a broad spectrum. At one end are simple mixtures that provide a pleasing contrast to the food itself, or add a flavor that it lacks. Melted butter offers a subtle richness, vinaigrette salad dressings and mayonnaise a tart richness, salsas tartness and pungency. At the other end of the spectrum are complex flavor mixtures that fill the mouth and nose with sensations, and provide a rich background into which the flavor of the food itself blends. Among these are the meat-based sauces of the French tradition, whose complexity comes largely from the extraction and concentration of savory amino acids and other taste molecules, and from the generation of meaty aromas by way of the browning reactions between amino acids and sugars. Chinese braising liquids based on soy sauce are similarly complex thanks to the cooking and fermentation of the soybeans, while the spice blends of India and Thailand and the moles of Mexico typically combine a half dozen or more strongly aromatic and pungent ingredients.