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Biology · a two-minute test

Put sugar on the back of your tongue. The tongue map says that’s where bitter lives.

The tongue map, sweet at the tip and bitter at the back, is still drawn in a Romanian biology textbook approved in 2024. But every part of the tongue that has taste buds tastes every taste. Check it on your own tongue with sugar water, then see how four tables from 1901 turned into a map.

Do the testWith a whole class
bittersoursoursaltsaltsweet
The textbook map, redrawn: sweet at the tip, salt beside the tip, sour on the sides, bitter at the back. The dot marks where the sugar goes.

What the textbook says

The grade 7 biology textbook from the Romanian publisher Litera, by Alexandrina-Dana Grasu and Jeanina Cîrstoiu, approved by the Ministry of Education in its 2024 tender, draws a tongue with four coloured zones on page 51. The text beside it reads:

“Figure 24 shows a ‘taste map’, with the zones that receive a particular taste. Some zones overlap. Sweet taste is received at the tip of the tongue, and salt at the tip and the edges. Sour taste is received on the edges of the tongue, and bitter at the base.”

Biologie, manual pentru clasa a VII-a, Litera, 2024, p. 51 (our translation)

In the figure, the zones overlap only at the tip and along the edges; the back of the tongue is coloured “bitter” alone. In the textbook’s digital quiz, “Sweet taste is perceived at the tip of the tongue” must be marked true, and “Bitter taste is perceived over the whole surface of the tongue” false. Strictly, the middle of the tongue does taste very little; but bitter is tasted over all the rest of it, not only at the base.

At the “George Emil Palade” National Biology Contest, county round, 6 April 2024, item 52 for grade 7 has Ana drink hot milk that damages her taste buds, “especially those towards the tip of the tongue”. Pupils must say which tastes she lost. The answer key: “sweet and salty”, exactly the map’s zones at the tip. In item 41, pupils had to accept that sweet “can be perceived” at the tip and bitter towards the base, which is true, just not only there.

The textbook also sets a practical: “Working in groups, a taste map can be made for different subjects.” It ends by asking: “What is the conclusion of this experiment?” The test below is that experiment.

Romania is not alone: the map spread through textbooks in many countries over the second half of the twentieth century. Romania is the example here because its current textbook and contest papers are online, page by page.

The test: your own tongue map in two minutes

You need sugar, water, two glasses and a few clean cotton buds. The handle of a teaspoon works too.

  1. Dissolve two teaspoons of sugar in half a glass of water, about 8 grams per 100 millilitres. The second glass, with plain water, is for rinsing.
  2. Rinse your mouth, stick out your tongue and dab it gently with a tissue, so the solution stays where you put it.
  3. Dip the bud, shake off the drops and hold it on one spot for 2–3 seconds. Keep your tongue out until you answer, or the sugar spreads.
  4. Rinse with water between spots.
  5. At the back, aim for the large papillae at the rear of the tongue, a little to one side. If you start to gag, put the bud on the edge, as far back as you can, where the tongue has small folds: there are taste buds there too. Don’t use the middle of the tongue, which tastes very little, and don’t touch the roof of your mouth.

It is more reliable still with someone beside you: they pick the bud and you don’t know what is on it. That way what you already know from school can’t help you.

Two teaspoons of sugar in half a glass of water, well dissolved.

tipsidemiddleback
Your map
bittersoursoursaltsaltsweet
The textbook map

clearfaintnothing

Tip of the tongue: what did you taste?

Test the four spots in turn: tip, side, middle, back. Note on paper what you tasted at each. On the textbook map, sweet sits only at the tip; at the back the map puts bitter.

In class: everyone at once

Each pupil has a small cup of their own, or a clean cotton bud they dip only once. Nobody dips twice into the same cup, and every round uses a new bud. The teacher projects the screen below and starts the countdown.

Whole class

Sugar on the back of your tongue.

On the textbook map, the back of the tongue is “bitter”. Hold the bud there for three seconds, tongue out.

Eyes closed. Hands up if you taste sweet.

0 of 0

Hands up
Pupils in the room

Second round: lemon juice on the tip, where the 2019 edition of the textbook said sour cannot be tasted. Third, for anyone who wants it: tonic water on the tip. Tonic water contains quinine; anyone who must avoid quinine skips it.

Where the map came from: four tables from 1901 and a graph from 1942

In 1901, at Wilhelm Wundt’s psychology institute in Leipzig, D. P. Hänig used a fine brush to put solutions of sugar, salt, hydrochloric acid and quinine sulphate on the tongues of seven colleagues, each more dilute than the last, until they could no longer taste them. He worked at 14 points around the edge of the tongue and 14 more further in, between 3 and 5 in the afternoon, over four semesters. For each taste he published a table of thresholds: the weakest solution each person could still taste at each point.

1×2×3×4×5×6×times more sensitive than the weakest pointtipsidebaseABCDEFGHbittersoursaltsweet

In 1901, D. P. Hänig found all four tastes at every one of 14 points around the edge of the tongue. For sweet, the tip was 3.3 times more sensitive than the base; for bitter, the base was 6.3 times more sensitive than the tip. For salt and sour, the differences were 1.2 and 1.5 times.

The mean thresholds printed by Hänig (Philosophische Studien 17, 1901, tables I–IV), turned into sensitivity: 1 divided by the threshold. In Boring’s graph (1942, fig. 76), each curve is scaled to its own maximum. The letters are Hänig’s points.

The last two steps are our own calculation, made on the mean values Hänig printed. The psychologist Linda Bartoshuk traced the textbook map to Boring’s graph in 1978; in 2022 the psychologist Charles Spence, reviewing research on taste across the tongue, took up the argument that the graph made its way into many textbooks over the following decades. Hänig himself had warned, on page 617, that his curve drawings were only meant as teaching aids.

Why you can’t notice Hänig’s differences

Hänig’s thresholds are solutions so dilute you can barely taste them. The rim point least sensitive to sweet, at the base, needed a 1.16% sugar solution. Your glass holds about 8%, nearly seven times as much. At that strength you taste sweet wherever you have taste buds. A kitchen test does not measure how sensitive a spot is, so it cannot redraw Hänig’s curves. It can only check whether a taste is felt in a zone, and the zones on the drawing fail that check.

What we know today about where we taste

Threshold differences, no zones

In 1974, V. B. Collings measured thresholds again, in 15 people, at five places: the tip, the side, the foliate papillae, the circumvallate papillae and the soft palate. For salt and acid, the largest difference between places was about threefold. For quinine, the lowest threshold on the tongue was at the tip, and the lowest of all on the soft palate. At higher concentrations, though, bitterness grew fastest at the back.

With strong solutions, things shift a little. In 2014, Emma Feeney and John Hayes swabbed concentrated solutions on the tip and the back of the tongue of 122 people. Every taste tested was tasted both at the tip and at the back. For sweet, salty and sour the tip and the back did not differ significantly, while bitter and umami were more intense at the back. So the textbook’s “bitter” zone has a grain of truth: the back tastes bitter more strongly when there is a lot of it. The tip tastes it too.

Where the taste buds are

fungiform papillae: dense at the tipfoliate papillaecircumvallate papillaemiddle: filiform papillae, no taste buds
Schematic drawing; the papillae are drawn as a pattern, not counted.

Taste buds sit in three kinds of papillae. The fungiform ones, like tiny mushrooms, cover the front two-thirds of the tongue and are densest at the tip: in the people of the 2014 study, between 23 and 123 per square centimetre. The foliate papillae are folds on the sides towards the back. The large circumvallate papillae form a V at the base of the tongue. The rest of the surface is covered by filiform papillae, which have no taste buds. Taste buds also thin out away from the tip: in ten tongues examined under the microscope in 1986, they were on average 4.6 times denser at the tip than halfway along the edge. And in 1901, none of Hänig’s seven people tasted anything in the centre of the tongue.

We also taste beyond the tongue: on the soft palate, which in the 1974 measurements responded to all five substances tested, and in the throat. The hard palate, the lips and the inside of the cheeks taste nothing.

Every bud, every taste

Each taste bud holds different cells for different tastes: the cells for sweet, bitter and umami each carry receptors for one taste, sour has its own type of cell. In 2009, researchers from the same team wrote that taste buds from all regions of the mouth contain cells that respond to all five basic tastes. In 2006, Charles Zuker’s team wrote that, “contrary to popular belief”, there is no tongue map. The receptor for umami, the taste of glutamate described by the Japanese chemist Kikunae Ikeda in 1909, was identified in 2002.

Questions

Is the tongue taste map true?

No. Every part of the tongue with taste buds tastes all five basic tastes. Sensitivity varies from place to place, but the variation does not form separate zones.

Where on the tongue do you taste bitter?

Wherever there are taste buds. With strong solutions, bitter is tasted more intensely at the back of the tongue; at threshold, the 1974 measurements found the greatest sensitivity to quinine at the tip of the tongue and on the soft palate.

Which parts of the tongue have taste buds?

The whole rim of the tongue, including the tip and the base, where the fungiform, foliate and circumvallate papillae are. The middle tastes little or nothing. Within the tasting area there are no separate zones for sweet, salty, sour or bitter.

How many basic tastes are there?

Five are widely accepted: sweet, salty, sour, bitter and umami. The Romanian grade 7 textbook mentions umami too, placing it “over a large area of the tongue”, but leaves it off the map.

Is spicy a taste?

No. The capsaicin in chilli activates a heat and pain receptor, described in 1997, not a taste receptor. That is why chilli also “burns” on the skin.

Sources and method

The chart uses Hänig’s printed mean thresholds for eight of the 14 rim points (from the tip, along one side, to the middle of the base); the ratios in the text (3.3, 6.3, 1.2 and 1.5 times) are computed over all 14. Sensitivity is 1 divided by the threshold, as in Hänig. In the “1942” step each curve is divided by its maximum, as in Boring’s figure; in “The map” step each point gets the taste with the highest value after that division. That last step is a reconstruction, not a procedure anyone described.

The kitchen strengths are approximate (a teaspoon of sugar is about 4 grams). A kitchen test uses solutions far above threshold, so it can show whether a taste is felt at a spot, not how sensitive that spot is.

Hänig worked with seven people; each table uses four of them. The Chandrashekar et al. (2006) and Yarmolinsky et al. (2009) quotations, Bartoshuk’s 1978 link to Boring and her 1993 remark on Boring’s graph are taken from Spence’s review (2022).

Also about the body and textbooks, on this site