Oral astringency: a tactile component of flavor.

The psychophysical, chemical and physiological bases of the oral sensation of astringency are discussed in an effort to clarify the nature of this enigmatic sensation. It is argued that, despite recent data from animal studies that suggest it is a taste sensation mediated by the chorda tympani nerve, astringency arises primarily from increases in friction between mucosal surfaces. Evidence is discussed that supports the view that oral astringency results primarily from the precipitation of salivary mucoproteins, which impairs the natural lubrication of oral surfaces. The ensuing rise in friction induces sensations of dryness and roughness which, although subtle at first, can grow in magnitude over repeated exposures. These changes in the surface texture of the mouth are an important component of the 'flavor' of common foods and beverages such as fruits, nuts, teas and coffee.