There was a time when we happily thought the tongue could detect four more. MATT PRESTON
The hunt is on for the elusive “sixth taste”. We look at the contenders.
Our perception of taste has changed dramatically since the first major book about food was written in 1825. Jean Anthelme BrillatSavarin, a man with the rare honour of having a cheese named after him, endorsed the idea of four tastes – sweet, salty, sour and bitter – in The Physiology Of Taste. Today, we are discovering this may be just the tip of the taste iceberg.
Umami, first identified by Japanese scientist Kikunae Ikeda in 1908, is now widely accepted as the fifth of the primary tastes. It is the savouriness you detect in parmesan, tomatoes, Vegemite and fish sauce. But scientists aren’t stopping at five. A spate of contenders are vying for the sixth taste spot. Essential criteria: There are numerous criteria scientists use to identify when something is a taste. Many contenders fail three of these checkpoints.
Firstly, the new taste must be uniquely different from the other primary tastes. Secondly, it should trigger a biochemical reaction. Lastly, specific receptors must be found to identify the taste. So let’s assess each claimant’s case for the title…
Chilli heat or minty coolness: We certainly know about these when they are in our mouths, but our ability to discern the temperature of food is actually a matter of touch rather than taste – it’s a nerve reaction. The heat of chillies or pepper, and the perception of coolness with mint and menthol, are chemicals fooling our temperature sensors. Verdict: dismissed. Astringency: The mouth-puckering dryness you get from drinking stewed tea, sipping tannic red wine or eating an unripe banana is astringency. But that isn’t anything to do with your tastebuds. What’s happening is that the tannins cause the mucus membranes to contract, making this another mechanical reaction. Verdict: dismissed. Numbing: Both Sichuan and some Indonesian cuisines use prickly ash berries, aka Sichuan pepper, to give food a numbing quality. Rather than a taste, this is another example of chemesthesis, in which the chemicals in foods impact touch rather than taste. Verdict: dismissed. Metallic: Sometimes you get a metallic taste in your mouth, but this is caused by a reaction similar to the way a battery works. Electrical impulses are picked up by the mouth as a taste, even though it isn’t one. Verdict: dismissed. Calcium: There is a far better case to be made for the chalky or slightly bitter taste of calcium as the sixth sense. Scientists have found that mice have two taste receptors to detect calcium and one of those is found in humans.
Furthering the case for calcium is the survival of the species. As taste developed for human preservation, bitterness and sourness were signs of harmful foods while sweet, salty and umami promise something we should eat for the carbohydrates, minerals or proteins. So the fact that calcium is essential for human life means the body had a good reason for developing a way to identify it. Verdict: jury is still out. Oleogustus: That’s fat to you and me. In 2015, scientists at Purdue University, Indiana, claimed to have proved that fat is a primary taste. The tricky part is that the rich creaminess we taste and love is actually the feel of the fat, and when the taste can be identified it is a bit icky.
The fact that the actual taste of fat was recorded as being like rancid butter may mean our ability to taste it is also a preservation tool similar to picking up bitterness. Verdict: proven – almost. Starchiness: Last year, a research team at the University of Oregon found that human test subjects could taste the starchiness that makes bread, rice and other carbs, which might explain why we find pizza and pasta so desirable.
The ability to taste “glucose oligomers” was shown to be independent of our ability to taste “sweet” and now the researchers are trying to identify the receptors on our tongues that pick up this floury flavour. Kokumi: Scientists who championed umami’s acceptance as the fifth taste are also keen to make kokumi the sixth.
They’ve been claiming since the ’80s that kokumi is that sensation of richness you taste with braised, aged or slow-cooked meats, scallops, onions and garlic. Oh, and with milt, but as you are unlikely to be a regular consumer of fish sperm we can leave that one out.
But kokumi may just be part of umami and thus fail the “distinct taste” criteria. Verdict: inconclusive. Carbon dioxide: This might be the most bizarre claim for the sixth taste, but the evidence is compelling. That zingy fizz when drinking carbonated beverages was originally thought to be a function of touch – the feel of the bubbles popping on your tongue.
Back in 2009, research was presented that mice could taste an enzyme in CO₂. A similar find came in humans with a drug for altitude sickness which blocks the enzyme. Climbers who have taken the drug report that once they pop a bottle of bubbly to celebrate reaching a summit, the champagne tastes flat. Verdict: proven, your honour.
As scientists continue to unravel the complex secrets of flavour, calcium, starchiness and oleogustus are strong candidates to be declared primary tastes.
Proving this becomes increasingly complex as neuroscience asks questions about the impact of memory on taste, and the role of neurons that line our gut.
Until then, keep savouring food.
PASTA CRAVINGS If starchiness is the so much. Nettle spaghetti cacio e pepe. Recipe at delicious.com. au.