Karl Siebert (1); (1) Cornell University, Geneva, NY, U.S.A.
Technical Session 2: Sensory I
Sunday, August 14 • 9:45–11:30 a.m.
Tower Building, Second Level, Grand Ballroom
Taste is perceived by the tongue. We used to think there were four tastes—sweet, sour, salty and bitter—and that these were somewhat localized to different regions of the tongue. We have known for some time that there is a fifth taste, umami (savory), and that pores spread all over the tongue each contain sensors for all five tastes. Even more recent studies have indicated there is a sixth taste, oleogustus (fat). Beer contains little if anything that causes responses to the last two mentioned but is often accompanied by foods that do. Salty and sour sensations are detected through ion channels. Sweet, bitter and umami tastes are detected by G-protein–coupled taste receptors. Compounds perceived by taste can be either organic or inorganic (e.g., salty). Relatively high concentrations of sugars or salt are needed to produce a sensation. The sucrose threshold in beer is 2,600 mg/L. The chloride threshold has been reported by different groups as 560 or 1,100 mg/L and the sodium threshold as 560 or >2,400 mg/L. Sour can have a lower threshold (acetic acid threshold at 175 or 200 mg/L). Bitterness can be caused by quite low concentrations of isoalpha-acids (threshold at 4 mg/L). Olfaction occurs when volatile compounds reach the olfactory epithelium. This can occur either when inhaling (orthonasal olfaction) or when compounds from foods that are ingested and warmed are exhaled (retronasal olfaction). The olfactory epithelium cells directly enter the brain. Of the entire human genome the largest proportion devoted to a single function is that for olfaction (approximately 900 genes). Olfaction cells are G-protein–coupled receptors, and each cell expresses only one receptor type. Olfactory responses are produced by organic compounds that are generally less than 200 Da. A single compound can produce responses by different receptor cell types that vary in intensity, resulting in tens of thousands of response patterns. The thresholds of compounds that produce olfactory responses vary over nine orders of magnitude, from tertiary butyl mercaptan (0.0005 or 0.0008 mg/L) to ethanol (14,000 mg/L). Chemesthesis sensations are perceived by the trigeminal nerve, which wraps around the mouth and throat. This is a tactile (touch) sensor. It responds to physical sensations including astringency, smoothness, thermal heat and coolness, the tingling of CO2, etc. The hot and cold sensors cover the range from warm to painfully hot and from pleasingly cool to excruciatingly cold. Some chemicals can produce the same effect as thermal heat; these include capsaicin, the hot pepper compound, and gingerine, the ginger compound. Menthol and similar chemicals activate the coolness sensor. The compounds that produce chemesthetic sensations are mainly, but not exclusively, organic. Astringency, for example, can be produced by polyphenols and tannins, organic or inorganic acids, and multivalent metal ions such as aluminum. There is cross-modal interaction in flavor perception. What we smell influences what we think we taste and vice versa. When people experience flavor, the three or four most prominent sensations form the flavor impression.
Karl Siebert received a Ph.D. degree in biochemistry from Penn State in 1970. He then joined the Stroh Brewery Company in Detroit, MI, where he spent 18 years and held positions ranging from research associate to director of research. In 1990, he joined Cornell University as professor of biochemistry in the Department of Food Science, where he has continued to work on beverages, particularly beer. He received two MBAA Presidential Awards, and with his colleague, Penny Lynn, received the Eric Kneen Memorial Award (for the best paper in the Journal of the ASBC in the prior year) three times. He received the ASBC Award of Distinction in 1999 and the MBAA Award of Merit in 2011. Karl became an emeritus professor in 2014. He is active as a consultant in beverage technology and chemometrics, and occasionally presents a brewing extension program.