Immersion heater recall notice

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