What we experience as flavour we attribute to the mouth… but it’s a multisensory process

The sensation of taste is about 80% smell, but a crucial 20% comes from flavour, and we detect that with our mouths. Between 2,000 and 10,000 taste buds live there, and they’re not even limited to our big tongues (the only free-ended muscle in the human body), but the roof and walls of the mouth, the throat, and the oesophagus. This time, cranial nerves and taste bud receptors called papillae pick up microscopic flavour molecules from our food and drink, and send a signal over to the olfactory nerve endings in the roof of your nose. Ever been encouraged to breathe through your nose while chewing or drinking to maximise the taste? It’s to vacuum up these aroma and flavour molecules to the top of your nose and throat, where they are most warmly received. The nerve endings then signal the olfactory bulb on the underside of the forebrain. The bulb is responsible for sending smell “messages” directly to two more nerves in the brain that communicate with the brain area responsible for the perception of taste – the deliciously named gustatory cortex buried in the middle of our craniums. Aromas feel like they come from the mouth because their signals end here, along with the ones from taste. “What we experience as flavour we attribute to the mouth as it’s where the physical contact happens, but it’s a multisensory process,” explains Nikki Welch, author of The Pocket Guide to Beer and qualified gastronomist. It sounds like a long journey, but these signals take place over milliseconds.

We can smell over 10,000 smells. You can test how crucial they are to taste by pinching your nose while you eat a piece of apple, and then a piece of raw potato. They will be almost indistinguishable. Open your nostrils and the apple will be sweet, the potato a little bitter (and kind of disgusting). Sweet and bitter can be detected by the tongue, but only with a lot of help from the nose. They are two of five basic flavours we detect, alongside salty, sour and umami. Remember that tongue map from school? It’s total nonsense, a mistranslation from an early 20th century German manuscript. Scientists have now figured out that our tongues can detect flavours anywhere on its surface. And those five basic flavours? Actually, they can be broken down a lot more. “There are multiple receptors for each of the ‘tastes’ each playing a different role, for example, we have 32 different receptors for bitter, which can indicate poison that is potentially lethal or antioxidant which is more desirable as we age,” says Nikki. “It’s also widely thought that we have a receptor processing lipids – a fat receptor. And, just like our skin, our mouth is also sensitive to pressure, temperature and texture, which gives us the sensation of mouthfeel.”

The saying “one man’s meat is another man’s poison” comes to mind when considering how individual taste can be. “The intensity of receptors differs from person to person and is highly individual, the higher the intensity of receptors for a certain taste, the higher the sensitivity. So, someone with a sweet tooth for example would actually have a low number of receptors for sugars,” explains Nikki. The fewer the receptors, the more sugar someone needs before they register it as sweet. Blame your biscuit addiction on genetics! And broccoli haters can unite – sense of bitterness is also genetic. We have a receptor sensitive to sulphur compounds, like those found in dark leafy greens, which are typically aversive (and sometimes toxic – think strychnine or cyanide). But some people have an insensitive version, and better hope they don’t find themselves in an Agatha Christie novel anytime soon. Plus, those who hate coriander because it tastes like soap, but can’t fathom how others don’t detest it, the answer is again genetic. The consumer genetics company 23andMe researched this and came across two common genetic variants linked to people’s perception of “soapy” flavours, on a gene that codes for a receptor highly sensitive to the aldehyde chemicals that coriander contains.

As the brain is designed to identify patterns it takes all of these elements, along with sight and sound, and creates an image of the ‘flavour’ of what we are consuming

All of these perceptions and more come into play when we detect taste. Even vision and hearing is important too. “As the brain is designed to identify patterns it takes all of these elements, along with sight and sound, and creates an image of the ‘flavour’ of what we are consuming,” explains Nikki. Imagine the snap, crackle and pop of Rice Krispies and if you’ve got a sweet tooth, your mouth will surely water. Look at someone drinking a beer, and you’ll be rushing to the bar. Because of all these influences, food and drink manufacturers spend a lot of time developing and refining their products until they’re just right, concentrating on balance of basic flavours, mouthfeel, look and even sound.

“A combination of chemical and physical analysis is always used in conjunction with human perception” to measure taste in a manufacturing setting, says Nikki, who has worked with many wineries and Fallen Brewery in Stirling. “Some elements are obviously easy to measure through traditional chemical analysis: residual sugar, alcohol, volatile acidity, bacterial presence etc.” One laboratory technique used is gas chromatography, a process that separates a mixture, and is used to identify the volatile, and therefore aromatic, elements of a product. Nikki explains, “The product is ‘split’ into its volatile elements that pass out as a gas and the distinct elements are then identifiable.” Ion chromatography is a newer technique that is fast becoming the method of choice for detecting amino acids, peptides, and proteins, carbohydrates and alcohols in beer.

Analytical chemists at Shimadzu Europa explain the usefulness of amino acid analysis; “Even though the brewing water and quality and character of hops and barley can be controlled, environmental influences can lead to small variations in the concentration of the constituents and therefore its quality: the contribution of specific amino-acids in the formation of off-flavours as well as a positive effect of others on fullness and drinkability has been established.” Keeping check of any changes in composition and content of amino acids is an important measure when ensuring the consistency in quality of the finished beer. It even goes beyond that, with Drs Gesa Johanna Schad and Brigitte Bollige stating, “Quantification of specific amino acids can also offer an indication of adulteration and degradation during processing and storage or identification of counterfeiting of branded products.”

Above 100 IBUs, your brain cannot detect any further bitterness, so 130 IBUs in solution will taste no more tart than 120

The question remains, how do we measure something so intangible as taste with machines? Take bitterness. We have a scale, the International Bitterness Unit (IBU) scale, for quantifying the compounds in beer that make it bitter – mainly the iso-alpha acids in hops, as well as polyphenols and a few other select bittering chemicals. By using spectrophotometry to measure the amount of light these compounds absorb, analysts can measure their concentration in solution. The scale, introduced in the early 20th century, goes from zero to potentially forever, but realistically almost all the beers you’ll drink range between five (low bitterness) and 120 (mouth-suckingly bitter). This is because above 100 IBUs, your brain cannot detect any further bitterness, so 130 IBUs in solution will taste no more tart than 120. These measurements do not tell the full flavour story, however. IBU is a great tool for measuring consistency, but it’s only objective, and doesn’t account for the way other flavours can mask bitterness. Going on the IBU scale, porters and stouts are higher than even the gnarliest of hop-forward beers, yet their sweetness and body make it much less noticeable. As such, sensory analysis still plays a huge part in quality control. “Most industries have an accepted tasting code,” explains Nikki Welch. “The Wine and Spirit Education Trust’s tasting guide is globally accepted as the industry code for wine tasting to create an objective view of the product. Using highly trained individuals is still a major part of the process.”

Taste and language are not inextricably linked, hence the fun in going to a tasting evening and debating what flavours and aromas are coming from your geuze, lambic or pale. Machines are vital in detecting objective levels of compounds that are responsible for taste and aroma, producing their own language for brewers, bakers and canapé makers to literally read their products’ insides. “There are now e-noses and e-tongues being used that take all of the measurable data and then run pattern recognition software to replicate the human process,” says Nikki, but surely these will never replace the wonderful creativity of the human brain in coming up with flavour associations, such as Richard ‘The Nose’ Paterson’s description of the rare 1951 Dalmore as landing on his lips “like a kiss”. Taste is out there for us to capture and enjoy, so do it while you can. After all, taste buds age and become less sensitive over time, all the more reason to enjoy a rich, bitter, cocoa-esque, tumultuous, brazen and forest floor-like pint tonight.