Professor John Lovering described the experience in an interview with Melbourne Museum in 2012 for their Dynamic Earth exhibition. He was a professor of geology at Melbourne University at the time. ‘We got some of the samples and immediately we analysed [them]. Later on people started to do work on the organic composition of the meteorite, in which there’s about … 2% organic material … and about 10% water. A lot of funny things that you don’t find normally in meteorites. And the exciting thing is there has been the complexity of the organic compounds they found; many amino acids … the building blocks of life itself—are all present in this meteorite.’ Over the years more than seventy amino acids have been identified from within the meteorite. Of these, only nineteen are known from earth. The complexity of these and other organic compounds present in the meteorite demonstrate that the simple chemical building blocks necessary for life on earth can form in other places. This discovery was grist to the mill of scientists working on theories that life on earth was ‘seeded’ by meteorites such as the one that landed at Murchison.
What Professor Lovering found amazing was that all the building blocks for life, including amino acids, were to be found on a rock that came from outer space. One of the amino acids Lovering was referring to was glutamic acid. It is a string of carbon, hydrogen, nitrogen and oxygen atoms that form a compound that is an essential neurotransmitter in the brain. Without it we wouldn’t have memory. Without memory, what are we? Glutamic acid is also detected by your tongue. We detect it as a savoury, brothy, mouth-filling, pleasant sensation. It is one of the compounds that the tongue detects, giving us the sensation of savoury or, as the Japanese like to call it, ‘umami’. It sits alongside the sensations of saltiness, sweetness, acid and bitterness. Glutamic acid exists in the planet’s yummiest foods: parmesan cheese, dashi, mushroom, and meat—chicken, seafood, lamb, beef and pork. Glutamic acid is, in a word, delicious.
That a compound from outer space could be delicious struck me as remarkable. Why can our tongues detect glutamic acid but not, say, glass? Why can we taste monosaccharides and disaccharides—sugars—and not polysaccharides, which we know as starch? They are all carbohydrates.
A visit to one of the nation’s leading experts on the tongue and how it works unlocked the world of taste for me, with a few simple experiments. Russell Keast PhD is a professor at the Department of Exercise and Nutrition Science at the Centre for Physical Activity and Nutrition Research at Melbourne’s Deakin University. He’s an affable Kiwi who likes craft beer and good food. He put me through one of his regular taste tests that he applies to hundreds of people in order to gain raw data on how the human tongue detects compounds that we understand as ‘taste’.
Standing in his taste lab—all stainless steel benches, fridges of food, and lines and lines of tiny cups filled with small amounts of colourless liquids—Keast told me, ‘You know that tongue map you were taught at school. Well, it’s wrong. Mostly. There was a misinterpretation of a diagram developed in Germany in the early twentieth century. We have different tastebuds that can detect different compounds that we perceive as salty, sweet, sour, bitter and umami.’ He explained that although some of our tastebuds are more concentrated in some areas than others, we generally perceive all five tastes on all areas of the tongue. He was quick to point out, however, an essential point that anyone working in the food and wine industry needs to understand. ‘Not everyone tastes everything in the same way. Thirty per cent of people don’t detect bitterness very well,’ he said. ‘About the same percentage of people don’t detect umami unless they are trained to do so. Some people are very sensitive to saltiness and bitterness,’ he went on. ‘And, although it is not strictly a taste issue, 13 per cent of people not only don’t like coriander—to them, it is disgusting. It tastes like soap.’ When a herb that so many people love the flavour of is repugnant to a small but not insignificant proportion of the population, this poses real conundrums for chefs and diners alike.
His assistant ushered me into a dimly lit room full of booths partitioned off from each other. In front of me was a pen and paper. A hole appeared in the wall and a tray covered in rows of eight little plastic cups in a line was pushed towards me. Each cup contained an anonymous compound dissolved in water that would stimulate certain tastebuds. From left to right, each cup contained a little more of the compound than the previous one. I had to make a mark on the sheet of paper when I detected something on my tongue, and then make another mark when I knew what each cup contained. Sugar was easy. I caught on to that one in the eight cups pretty early on. Next up was acid—citric acid, I reckoned. I could detect that in small amounts. Bitterness—I am king. I could taste the bitter compound, what I learned later was a tiny drop of liquid caffeine diluted in a lot of water. When it came to salt it took me quite a few tastes in the line of cups before I could not only detect a difference but also work out exactly what it was that I was tasting. Not a good sign for my cardiovascular future. Then came the last set of cups to taste. It took four cups for me to realise that the water tasted, well, delicious. Clear, colourless water. But incredibly delicious.
Back in Keast’s lab it was revealed to me that the water was delicious because it was seasoned with dissolved monosodium glutamate, also known as E621 or MSG. This is a synthesised version of the naturally occurring compound glutamic acid, first isolated from wheat gluten in the late nineteenth century by German scientist Karl Ritthausen. Glutamic acid was again isolated from kelp, in the early 1900s, by Kikunae Ikeda, a researcher at the Tokyo Imperial University. He made kombu broth and concentrated it. Kombu is a type of kelp and a cornerstone ingredient, along with dried tuna, of the Japanese stock dashi. The tuna is not only dried but often fermented. Despite being a fine broth it is deceptively rich and very tasty. In it are several amino acids, which we find delicious. Glutamic acid is found in vegetables such as capsicum, potato and tomato. Many fungi, such as field mushrooms, porcini and oyster mushrooms, are good sources of it. Many fermented products, such as kimchi and salami, are high in glutamates, not only from the smaller amounts in the body of the substance being fermented but also from the little yeast cells that are doing the fermentation. Other compounds high in glutamates are fermented animal proteins such as cheese, jamón and anchovies, in which various fungi, bacteria or enzymes break down proteins into amino acids such as glutamic acid. Flesh in general is high in glutamic acid—not as high as preserved flesh, such as prosciutto, salami and cured fish, but still high enough to register as ‘delicious’ when it hits one’s tastebuds.
Another amino acid is aspartic acid, found in vegetables such as asparagus, which causes a similar savoury sensation in most people. This was one of the amino acids found in the Murchison meteorite.
That we are hardwired to detect and enjoy compounds formed in outer space but found in nutritious food has evolutionary advantages. As do all the compounds detected on the tongue. The neural pathways for our sense of taste were laid down in utero. Basically, nerves join our tastebuds to travel to the brain stem—the lizard part of our brain. We are hardwired to taste and don’t even need to think about it. It just happens.
We are hardwired to taste salt because without it we die. (Eat too much salt and you die too, but that’s another story). Salt is essential for the chemical reactions in our bodies. Think about proto-humans, primates who sourced all their food directly from nature without the intervention of any annoying modern conveniences, such as agriculture, mechanised food production or transportation. Unless you’re living by the shore, next to a salt lake or close to a seam of exposed subterranean salt, you’re going to need to find salt from the world around you. Salt occurs in small quantities in nature, in some plants, and is something we can source from the flesh and blood of other animals. Having the ability to detect a compound essential to survival by simply putting your tongue on it is a pretty cool tool to have.
An organ that can detect energy in an energy-scarce world is also a handy tool to have. Our tongues are equipped w
ith tastebuds that can detect about a tenth of a teaspoon of sugar (disaccharide) dissolved in a cup of water. More simple sugars, such as fruit sugar (fructose, a monosaccharide) and honey (a mix of two monosaccharides—glucose and fructose), we can detect at marginally higher concentrations. These are all compounds that are packed with molecules the human body can easily untangle and burn as fuel, or turn into fat for later use. In other words, our tongues detect compounds with energy and we love the taste.
But wait! There’s more! Our tongues are like Swiss Army knives helping us survive the poisonous arsenal produced by plants in self-defence. Our sense of bitterness is hardwired for survival and is our first line of protection against poison. Many poisonous plants have evolved to produce alkaloids to guard themselves from pest attack. We detect alkaloids as bitter. Unlike mild saltiness, bitterness is generally unpleasant. Many brightly coloured berries are poisonous, but many others are nutritious. A human who can detect bitterness in small quantities is a good human to have around in a small group of hunter-gatherers. On the flip side, some of our favourite pastimes involve consuming bitter substances. Beer is bitter. Coffee is bitter, as is tea, thanks to the caffeine and tannin. Wine can have bitterness. Chewing tobacco is bitter, as is chewing hashish. It seems the bitter substances we have become most fond of have rewarded other parts of our brains with chemical versions of excitement or pleasure.
Theories on why we have evolved with an acid-detecting tongue are a little more complex. Award-winning wine writer Max Allen hypothesises that the human tongue evolved to detect changes in pH in liquids. This was an indicator that very ripe fruit had gone beyond its optimum ripeness and begun to ferment. Alcohol is an energy-dense food and therefore desirable to proto-humans in an energy-scarce world. Although I strongly support Allen’s theory, there are those who suggest that acid detection alerts us that food is of such a low pH that it could disrupt the efficient digestion of food if eaten. Or, in the words of my mother when she somehow knew we were going off to filch apples, ‘Don’t eat the unripe ones, as they’ll give you a tummy ache’.
As far as a palate hardwired for compounds that are ‘delicious’, the theory seems to be that although the human body can synthesise non-essential amino acids such as glutamate, these are often found in conjunction with other amino acids that are not as tasty but are essential to our wellbeing. For example, crab is delicious. The compound that gives crab its unique taste is an amino acid called arginine. Arginine in itself is quite bitter, but in crab it is also found with glutamate. Together they are delicious. Sea urchin is a similarly delicious living creature, which contains another bitter amino acid called methionine. But sea urchin is also packed with glutamic acid. The body cannot synthesise methionine as it can glutamic acid. The fact glutamic acid occurs so frequently alongside other amino acids seems to be the common factor. While we don’t necessarily need to eat glutamate, as the body makes its own, it is found alongside essential amino acids that we do need and can’t make ourselves.
At this point it is probably important to point out that MSG is a salt of glutamic acid and is made from plant extracts to form translucent crystals that are used extensively in the food industry as a flavour enhancer.
The amazing thing about our ability to detect deliciousness is that it is easily manipulated to create an overwhelming sense of umami. There are two other truly delicious amino acids commonly found in the food we eat. Other tasty, non-essential amino acids are guanylate and inosinate. When they are combined together or with glutamate, they can overwhelm the tongue, lips and cheeks with an enduring and lingering sense of pleasure that some find analogous to coital overload.
This is a synergistic effect that is common knowledge for and second nature to Japanese chefs but is just dawning upon almost all Western chefs. In the north-east Victorian town of Beechworth, chef and former chemist Michael Ryan explained to me a little of the science behind why these amino acids make food taste good. ‘Seaweed, particularly kelp, is naturally high in an amino acid called glutamate,’ he said in quiet, measured words. ‘Combine kombu with dried shiitake mushrooms, which are high in guanylate—another amino acid—or with bonito, which is high in inosinate, and something amazing happens,’ he said. ‘There is a synergy between these natural compounds that gives you a very strong sensation of umami. The effect is remarkable.’ Ryan proves this in his dish of kingfish poached in dashi and then brushed with iwa-nori, a jam made by cooking down nori sheets with sake and sugar. This is served with a salad of cucumber and sea spaghetti, seaweed that is imported from Spain, plus a little of a native seaweed grown on a farm in East Gippsland. It is sensational. Similar effects are achieved when cheese is washed down with cider, the yeast cells releasing glutamate upon their demise. Classic matches include asparagus served with parmesan cheese. Avocado and tomato. Anchovies and sherry. Four ’N Twenty pie and sauce.
This line of investigation had proved so fruitful; some areas of exploration are dead-end rabbit holes. This little journey into the role of amino acids in our diet had uncovered the most profound idea. Life on earth possibly started with organic compounds that landed on it on rocks from outer space; we are all born with organs that can taste those rocks and we find those rocks delicious.
Before I left Professor Keast he sent me on one last quest. Back in the booth I had eight little cups in front of me. I tasted each one, rolling the cool liquid over my tongue. After the fourth I paused. It was different, but I didn’t recognise the taste. A slightly tingling sensation on the tongue, but not one of the other five taste sensations. With each cup the sensation grew stronger. I could ‘taste’ something but couldn’t tell what it was. ‘That’s fat,’ explained Professor Keast. ‘We haven’t proved it yet but I think it won’t be long and we will have enough data to put forward in an academic paper that the human tongue can detect fat. Imagine the implications of that.’
It was in February 2015 that Keast and his team made the announcement to the world. Fat was the sixth taste. He published a paper in the peer-reviewed journal Flavour.
After half a decade’s research and subjecting 500 volunteers to taste trials, Professor Keast proved the human tongue had tastebuds that could detect the presence of fatty acids at levels as low as ten parts per million. He said at the time, ‘We were using oleic acid that is found in many everyday foods such as olive oil, canola oil, meat and dairy products.’ Subjects were placed in isolated booths, the same as the one he had placed me in earlier, and asked to taste clear cups of water into which was placed tiny amounts of fatty acid. Around 40 per cent of people detected the fatty acid at very low levels, around ten parts per million, and this figure increased to 80 per cent at 100 parts per million. Keast said the detection of fat by tongue does not give a ‘conscious perception of taste quality such as sweet or saltiness’; instead, participants in experiments could detect a different sensation on their tongue.
‘In high concentrations of fatty acids, subjects reported an unpleasant sensation,’ Keast said. ‘We [scientists] think that this could be an evolutionary response signalling that the fat in the food may have broken down over time and not be fresh or nutritious.’ It is interesting to note that many people cannot consciously detect the sensation of umami or savouriness unless they are trained to do so. Perhaps, with training, we will be able to be conscious of the sensation of fat on our tongues on a day-to-day basis. Keast suggested that people who detect fatty acids also associate the taste sensation with the feeling of being full and that people who have difficulty in detecting fatty acids are often obese. Sensitivity to fatty acids can be increased by going on a low-fat diet, after which the ability to detect fatty acids increases and, by association, the ability to feel full.
An extra taste is an amazing discovery. It is as if science detected another colour that sat between yellow and green on the spectrum. A colour that had been there all along that we simply hadn’t been trained to see. I have practised to see if I can taste fat. It’s hard. You have to really concentrate
, as there is so much other information going on in the mouth and nose. It’s as if we’re not really meant to be able to recognise it. The sensation pops up when I least expect it. Eating a store-bought biscuit. Chewing oats in muesli. The lingering tingling after eating something with egg mayo. The sensation is not always there but, like many things in life, once you learn about it, you can never unlearn it.
8
Umami by Numbers
After my brush with the extraterrestrial and fat tastebuds, it was time to come back down to earth and put some newly learned theory into practice. Knowing that we naturally crave umami, I set out to look at ways of identifying sources of umami in the meat-free world.
One of the most common sources of umami in the average kitchen is the humble tomato. It contains 120 milligrams of the savoury-tasting amino acid glutamate per 100 grams. A fully ripe tomato, harvested ripe on the vine, can contain as much as 270 milligrams of glutamate per 100 grams. A tomato harvested pink then gas-ripened will contain around 70 milligrams per 100 grams. This little measurement of glutamate helps explain why supermarket tomatoes, and other veg, are not as delicious as they used to be. Supermarket tomatoes are not harvested when vine ripe but when ripe enough to reach the ‘correct’ colour by the time they are trucked, stored and sent to the supermarket. The level of glutamate rises as the tomato ripens. When a ripe tomato is dried, the flavour is concentrated even further and you can end up with a whopping 620 milligrams of glutamate per 100 grams. This is getting close to Cabrales cheese, a blue cheese from Spain, at 760 milligrams per 100 grams. One of the most intense umami hits you can have in your fridge is parmesan cheese, which weighs in at a mighty 1200 milligrams per 100 grams.
My Year Without Meat Page 7