Hi all,

Recently Nigel posted on TeaMail the following cogent and detailed
description of taste sensation which I found particularly enlightening.
Nigel explains terms and writes in a manner that allows me to concentrate on
the subject at hand without thumping through a dictionary every other
minute. I'm quoting his post here with his permission. I've also posted it
to TeaDisc. For your information and tea entertainment.

Michael

QUOTE NIGEL
Tasting, gustation, or mouth physiology as Michael puts it, is
complex. Basically we have taste buds located in groups or papillae
mainly on the upper surface of the tongue, though a few are present
on the soft palate, uvula, and the top third of the oesphogus. Each
papilla has some 250-275 taste buds, 50 of which would fit on a
regular full stop. An adult human has around 10,000 taste buds each
of which regenerate every 10 days. Taste is most acute in youth with
a distict loss after 45. By age 75 taste bud density has fallen to
half of normal adult level, though fortunately for old tea tasters,
regular practice can increase acuity (sensitivity) by ten fold.
Gender also affects acuity with women having slightly higher
sensitivity, peaking at ovulation.

Just six tastes can be recognised and detected by the taste buds -
sweet, salt, sour, bitter, umami (savory), and metallic.

Human sensitivity to a particular taste varies enormously. For
sweetness (sucrose) we can recognise it to a dilution of 1 in 200,
for salt (common salt) to 1 in 400, for sourness (citric acid) to 1
part in 130,000, and for bitterness (quinine) to 1 part in 2 million.

In testing your tasting (so to speak) there are four thresholds:
Absolute threshold - the concentration at which you can recognise
that something has been added.
Recognition threshold - the point at which the additive can be
identified (e.g salt)
Difference threshold - how much additional additive needs to be added
for a difference in level to be detected
Terminal threshold - the point at which you do not detect additional
amount of additive - sensory overload.

With normal tea tasting (and ignoring olfaction - our ability to
detect and recognise volatile aromas) we are generally concerned with
our ability to detect sweet and bitter and to a much smaller extent
sour and umami. However as Michael points out Astringency is
important - this is however not a true taste as it is not picked up
by the taste buds and thus there is not a true sour to astringent
spectrum or continuum . Astringency is sensed when slick proteins on
the surface of our mucous menbranes are denatured by, for example,
tea flavanols or by unripe banana skin. The usually slick surface
that our tongue runs past easily and unconsciously becomes "rougher"
and noticeable (= puckery) when this denaturing occurs. Experts in
the field suggest that the sense picking up astringency is tactility
(feel) and kinesthetic (feedback from muscles) and there may be a
slight trigeminal effect (sense of pain).

While we can make model tasting systems using standard chemicals
(sugar, quinine, MSG, etc) the tastes of things in real life are more
complex. A lemon will combine sweet and sour as will buttermilk. A
grapefuit will combine sweet and sour and bitter. But hera another
effect may come into play - too much of a sour or bitter chemical may
cause denaturation of mouth protein to add astringency to the mix. A
Gyokuru may combine sweet and bitter and umami and astringency (even
before we come to the olfatory contributions) and each of these
tastes may vary with respect to the other - to our pleasure or
displeasure. In learning tea tasting we have to learn the basic
tastes and recognise the "good" and the "bad" combinations while
remembering that too little of a good one can be just as bad as too
much of it (bitterness for example).

I hope I have helped clarify a little the issue of taste in tea
tasting - though it ignores the importance of the senses of sight,
sound and smell in the appreciation of tea - all just as complex. I
guess this is why tea tasting is traditionally an apprenticeship -
repeatedly reinforcing perceptions against set standards, rather than
a process of cognitive learning.

Nigel at Teacraft
UNQUOTE NIGEL