Any flavor or gustatory perception that could be roughly described as acidic or caustic is called a sour taste sensation. We use words like soapy, tart, corrosive, sharp, astringent, tangy, acerbic, rancid, vitriolic, biting, vinegary etc. to identify these flavors. To make a binary description of a sour sensation compare it to tasting a lemon. Report the result using one of the following algebraic statements. If the two experiences are not comparable, then say that the sensation is not a sour sensation and express this as . If the sensation is like tasting a lemon, then say that it is *tart*. Write this as . If the sensation is not like tasting a lemon, then say that it is *soapy* and that . The number is called the **sourness**. These relations are mathematically expressed by

## Reference Constant for Sourness

The numerical constant associated with tasting a lemon has not yet been determined.