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.
