Sour-Bitter Confusion

There is a phenomenon in the sensory world widely referred to as the sour-bitter confusion that commonly occurs among untrained assessors. This occurrence involves the assessor describing a sour sensation as bitter and/or a bitter sensation as sour, with the former being more predominant. This practice appears to be limited to predominantly English-speaking countries such as the United States, Great Britain, and New Zealand6. Debate in the past has centered on whether this confusion stems from a physiological disorder or simply a deficit in exposure to and training with sour and bitter tastes4,5,7.
 
Bitter and sour are two of the basic tastes and are found in a wide variety of foods and beverages to help balance the products flavor profiles. Compounds such as amino acids, peptides, esters, lactones, phenols and polyphenols, methylxanthines, flavonoids, terpenes, sulfimides, and organic and inorganic salts contribute to the bitter tastes in products such as coffee, tea, chocolate, and some fruits and vegetables2. Sour tastes are associated with hydrogen ions and organic acids and are found in such sour foods as jams and jellies, buttermilk, processed meats, sauerkraut, and other products1.
 
Despite different compounds contributing to the sour and bitter tastes in foods, several studies have recorded subjects frequently confusing the two terms when attempting to describe simple solutions made with sour and bitter substances. In a study conducted by Meiselman and Dzendolet5, 80 subjects tasted 10 mL aliquots of 15 mM sucrose (sweet), 50 mM NaCl (salty), 2 mM HCl (sour), and 20 mM KCl (bitter) and asked to describe the basic taste perceived for each solution. While all types of confusions were made, the sour-bitter confusion was the most common error made, occurring in 21.25% of the subjects (sour being called bitter more frequent than vice versa). The scientists then instilled a correction procedure in an attempt to train the subjects on the different tastes, but 35% of these subjects still made the sour-bitter error. These results led the researchers to attribute the sour-bitter confusion to a physiological defect analogous to abnormal color vision.
 
OMahony et al.6 conducted a large series of experiments in an effort to better understand the sour-bitter confusion. Some of the experiments were modifications of past work conducted3,4,5,7, while others were new designs. Of the new experiments, variations included using students in both the United States and Great Britain, inclusion of correction procedures when naming errors occurred, and varying the concentration levels of the simple solutions used in testing: sucrose (sweet), NaCl (salty), citric acid (sour), and quinine sulphate (bitter).
 
The results of these experiments clearly demonstrated the sour-bitter confusion with 13.3% of all 1629 responses for sour and bitter stimuli involving citric acid being called bitter and 7.7% of the responses involving quinine sulfphate being called sour. The authors offered several explanations as to why the subjects had difficulty distinguishing between sour and bitter tastes. One hypothesis is that the subjects have more cultural experience with sweet and salty foods than sour and bitter foods, allowing their perception of sweet and salty to be more clearly developed than sour and bitter. A second hypothesis is that subjects are more familiar with sucrose and salt in their pure forms than citric acid and quinine sulphate, again allowing the subjects to better develop their own personal concepts of sweet and salty versus sour and bitter. A third hypothesis involves the incorrect cultural labeling of typically sour foods as bitter, as in the case of bitter lemon. In regards to these hypotheses, the authors concluded that the sour-bitter confusion can be attributed to a lack in the clear understanding of the definitions of sour and bitter rather than a physiological defect6.
 

References

 
1 Da Conceicao Neta, ER, Johanningsmeier, SD, and McFeeters, RF. 2007. The chemistry and physiology of sour taste a review. Journal of Food Science. 72(2): R33 R38.
 
2 Drewnowski, A. 2001. The science and complexity of bitter taste. Nutrition Reviews. 59(6): 163 169.
 
3 Gregson, RAM and Baker, AFH. 1973. Sourness and bitterness: confusions over sequences of taste judgments. British Journal of Psychology. 64: 71 76.
 
4 McAuliffe, WK and Meiselman, HL. 1974. The roles of practice and correction I the categorization of sour and bitter taste qualities. Perception and Psychophysics. 16: 242 244.
 
5 Meiselman, HL and Dzendolet, E. 1967. Variability in gustatory quality identification. Perception and Psychophysics. 2: 496 498.
 
6 OMahony, M, Goldenberg, M, Stedmon, J, and Alford, J. 1979. Confusion in the use of the taste adjectives sour and bitter. Chemical Senses and Flavour. 4(4): 77 94.
 
7 Robinson, JO. 1970. The misuse of taste names by untrained observers. British Journal of Psychology. 61: 375 378.