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In the early 1900s, physiologists recognised four basic tastes: sweet, sour, salty and bitter. A Japanese chemist thought that was one short. Kikunae Ikeda noticed that a simple seaweed broth had a taste none of the four could describe, and he used classical chemistry to find the molecule responsible. This post covers who he was, how he isolated it, a worked example with his own numbers, and why it took decades for the rest of the world to agree.
Who was Kikunae Ikeda?
The University of Tokyo's School of Science profile of Ikeda, written by chemistry professor Shin-ichi Ohkoshi (archived copy), gives these facts:
born in 1864 in Kyoto
enrolled in chemistry at Tokyo Imperial University in 1885 and graduated in 1889
from 1899 studied for two years in Leipzig in the laboratory of Wilhelm Ostwald, then a centre of physical chemistry
returned to Japan in 1901 as a professor of chemistry, and introduced physical chemistry to Japan
The profile adds that Ikeda, who grew up in Kyoto, had been interested in seaweed broth since childhood.
Why did Ikeda think there was a fifth taste?
In his 1909 paper, published in English in 2002 as New Seasonings in Chemical Senses, Ikeda wrote that physiologists recognised only four tastes and treated others as mixtures. He disagreed: "I believe that there is at least one other additional taste which is quite distinct from the four tastes." It was the taste he called "UMAI" (brothy, meaty or savoury), most characteristic of broth made from dried bonito and the seaweed Laminaria japonica. He then wrote: "I propose to call this taste `UMAMI' for convenience."
How did he isolate the umami substance?
A commentary in the same journal, The Discovery of Umami by Bernd Lindemann and colleagues (2002), describes his method. Ikeda started from the seaweed in dashi, a Japanese soup base, and used classical steps: extraction with water, removal of mannitol, sodium chloride and potassium chloride by crystallisation, lead precipitation and many further steps. Low-pressure evaporation finally gave slow crystals of a single substance, C5H9NO4: glutamic acid. Lindemann notes he did this with the help of just one technician.
The University of Tokyo profile supplies the scale: in 1907 Ikeda used the liquid from simmering 38 kg of dried kelp and extracted 30 g of monosodium L-glutamate. On 24 April 1908 he applied for a patent for a method of making a seasoning with glutamic acid as its key component, and it was registered on 25 July 1908.
Worked example: how much glutamate was in the kelp?
Use Ikeda's numbers and atomic masses C = 12, H = 1, N = 14, O = 16, Na = 23.
Yield. 30 g from 38 kg = 30 / 38,000 x 100 = 0.079%, under a tenth of one per cent.
Molar mass of glutamic acid, C5H9NO4: 5 x 12 + 9 x 1 + 14 + 4 x 16 = 60 + 9 + 14 + 64 = 147 g/mol. PubChem lists 147.13.
Monosodium glutamate, C5H8NNaO4: one hydrogen is replaced by sodium, so 147 - 1 + 23 = 169 g/mol. PubChem lists 169.11.
Moles extracted. 30 / 169 = 0.18 mol.
Sodium content. In MSG, 23 / 169 = 13.6% sodium by mass. In table salt, NaCl, it is 23 / 58.5 = 39.3%.
A yield that small means a great deal of material has to be processed to get a few grams of pure crystals, which is part of why the isolation was such patient work.
Why was umami slow to be accepted?
Lindemann and colleagues give several reasons. Ikeda's detailed paper appeared in Japanese. Umami is mild even at high concentrations. And glutamate, an anion, always comes with a cation whose salty or sour taste confuses the test. Umami research only grew on a larger scale from about 1980.
The molecular evidence came later. In 2002, Nelson and colleagues reported in Nature an amino-acid taste receptor made of two proteins, T1R1 and T1R3. Lindemann's commentary notes that in humans this receptor responds preferentially to L-glutamate, and that the response is enhanced by IMP, a nucleotide.
Common mistakes with glutamate chemistry
Confusing glutamic acid with glutamate. Glutamic acid is the neutral molecule; glutamate is the anion; MSG is its sodium salt.
Forgetting the charge forms. Amino acids carry both an acidic and a basic group, so they can exist as zwitterions. Our post on amino acids and zwitterions explains how.
Mixing up mass percentage and mole ratio. 13.6% sodium by mass is not the same as "one sodium in 19 atoms".
If amino-acid structures and charges keep blurring, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can revise each idea on its own.
What can a student take from how Ikeda worked?
Take an everyday observation seriously. A familiar broth started a research programme.
Name what you find. Calling the taste umami gave others something specific to test and argue about.
Expect slow acceptance. Good evidence can still wait decades for the tools that confirm it.
Practice routine: pick three amino acids from your NCERT chemistry book, write their formulas, calculate each molar mass, then the mass percentage of nitrogen in each.
Next step: calculate how many grams of sodium are in 1 g of MSG, then in 1 g of table salt, and compare.
