Ever since the days of Plato, scientists have more or less accepted the fact that there were only four basic tastes - salt, sweet, sour and bitter. About a decade ago, researchers, primarily in Japan, became extremely excited and reported that they had discovered a fifth taste - "umami". In the last month or two, largely due to reports in several respected neurological and epidimeology journals, the popular press has been jumping on the umami bandwagon with a passion.

Looking at the reality of the issue, although some scientists are convinced that umami is indeed a unique taste, others deny this, stating that the sensation caused by umami is simply a taste enhancer. So controversial is the subject that some highly respected scientists refuse to even discuss it, claiming that even the merest mention of umami would be to give credit to a non-existent phenomenon. On the other hand, some who support the idea are so enthusiastic that it is difficult to know whether they are talking about scientific fact or metaphysical castles in the sky. In Japan most people are ignoring the controversy and umami is the newest rage for seasoning foods.

To gain even an introductory understanding of umami, a certain amount of historical and chemical knowledge is required. Yoav Baruch, one of the serious researchers in the field of sensory evaluation informs us that the genesis of the discovery of umami came about early in this century when Japanese investigator Ikedo separated the material we now know as monosodium glutamate (msg) from the seaweed known as Laminara Japonica. It was not long until msg became known as an important taste enhancer, one that highlighted the taste of seafood and other foods. It has taken nearly a century, but MSG, which is a chloride salt of glutimate oxide, has now been identified as the material most responsible for the taste now called umami.

Baruch explains that two basic chemical groups share the responsibility for producing the taste of umami. The first (of which msg is an example) are created by groups of l-amino acids and the second is a group of ribonucleotides, an example of which is inosene monophosphate (IMP). Baruch goes on to say that researchers have found that the materials in these two groups cause the umami taste sensation in humans as well as in animal laboratory animals.

One of the tests that have been conducted towards the goal of determining whether one can really call umami a fifth taste was carried out by Japanese researcher Yamaguchi. His method was to ask people to taste various materials and to indicate to what extent the taste of each material was different one from the other. The result, which he adapted to a three dimensional scale in the shape of a pyramid (see the diagram), showed that within the pyramid there were four peaks, each representing one of the traditionally accepted basic tastes. Parallel to the pyramid, however, the materials belonging to the two groups that make up umami were identified as outside and thus separate and different from any of those tastes. Yamaguchi, Baruch and others use these findings as evidence to show that the umami taste can be considered as a separate taste with its own unique qualities.

Even though Baruch feels that the evidence for the phenomenon of umami is conclusive, he points out that there are researchers, especially in the Western world, who perceive umami (like msg) not as a unique taste but as a combination of already recognized tastes, especially those of sweet and salty.

Whatever side of the argument one takes, however, certain phenomenon associated with umami are undeniable. For example, the combination of msg nd IMP materials produce a synergism in the taste of umami - that is to say, the two together create a stronger sensation of taste than either alone, far more, in fact than from the same concentrations of one material aloneand not from both together. Even though some of the taste buds seem to specialize in that they are moresensitive to one or another of the basic tastes, nearly all of the taste buds react to some degree to all of the tastes. Yoav Baruch states that several options have been suggested that might explain the molecular mechanism of the sensation of taste of umami. The first is that the umami taste operates through those taste buds that are most sensitive to sodium; the second is that there are receptors that are specific to the taste of umami (as others would be, for example to the taste of sweet or bitter). The third option, says Baruch is that the materials that make up the umami taste temporarily changes the character of the receptors that specialize in other tastes, strengthening or emphasizing the typical taste of this receptor.

When asked to describe the taste of umami, Baruch and several other researchers report that "it reminds one very much of chicken soup". Chicken soup is a universal and has its variations in homes of Jewish, Shinto, Hindu, Christian and Moslem families. That umami has a definite place in the world of taste enhancers is already unquestionable. Whether it will eventually be definitively accepted as "the fifth taste" or will simply become a new source for jokes about Jewish and other mothers remains to be seen.

As to those who have voiced doubts about the health aspects of using msg and umami, Baruch points out that the prestigious Institute of Food Tecnhologists (IFT) in the United States has declared that msg is safe for usage with a vast majority of the population. Although the IFT recognized that some people report negative reactions, these are the exception and not the rule. They indicate further that millions of people have negative reactions to a vast variety of food products (including among others, gluten, peanuts, shellfish and chocolate) and that discrimination against msg (and by implication, against umami) is uncalled for.

Note of thanks: The writer is indebted to senior researcher Yoav Baruch for his cooperation in writing this article. For further information, Baruch can be reached by mail at Analyst Research Laboratories, Kiryat Weizman, Rehovot, Israel or by telephone at 972 8 6406949.

© Daniel Rogov