The Critical Palate

By M.S.

To a food critic, the word tasting summons delectable images of cheese and bread, foie gras and caviar, chocolate and wine-the usual subjects of such comparative evaluations. But at a 90-minute tasting conducted by Dr. Linda M. Bartoshuk in her laboratory at the Yale-affiliated John B. Pierce Foundation, the only samples I was offered were tepid, clear chemical solutions. They were washed over my tongue or used as a mouth rinse as I leaned over a sink or a funnel hooked up to a waste pail.

Odorless chemical stimulants were employed to activate the four basic tastes-bitter, salty, sweet and sour. The tests were both qualitative, meaning that I was asked to identify each taste at very low concentrations, and quantitative, meaning that I was asked to rate the intensity of different concentrations. During Bartoshuk's "whole-mouth" test, when I rinsed with the diluted solutions, I wore headphones and was asked to rate the strength of sound tones administered intermittently by Dr. Lawrence E. Marks, an auditory psychophysicist. This procedure, known as magnitude matching, is used as a form of control. Psychophysicists have found that a subject's perception of strength in taste concentrations usually matches the strength rating of comparable intensities of sound. Throughout the test, I wondered how my palate (used in the broadest sense) would rate. At first I hoped it would be judged "super," but then I felt that would mean my taste judgments might not be typical enough to be reliable for nonprofessionals. No need to have worried. Dr. Bartoshuk found that I matched the norm on intensity ratings. However, my sensitivity to tastes at very low concentrations was well above normal. That is due partly to naturally low thresholds but also to my experience as a taster.

I turned out to be a strong taster of the bitter stimuli phenylthiocarbamide (PTC) and propylthiouracil (PROP). The ability or inability to taste these stimuli is genetic. To taste very weak concentrations, as I did, indicates that the subject is probably homozygous, or has two dominant genes for bitter tasting. People who perceive PTC/PROP mildly are likely to be heterozygous, meaning that they have one dominant and one recessive gene. Non-tasters of these bitter stimuli have two recessive genes. It was interesting to notice how the tastes literally "felt" as they were being washed over the tongue. Salt and sweet were warm and pleasant; sweet was the most relaxing and salt was exhilarating. Bitterness curled the edges of the tongue. Sour felt icy and caused the surface of the tongue to contract. --M.S.