A lot has been written about the impact altitude has on taste. How being inside a noisy metal tube with lots of other people, at a lower air pressure and humidity than normal, greatly affects the ways we experience food and drink.
In truth, most of this is based on guesswork and personal anecdote. It’s quite hard to do the sorts of controlled studies that would enable us to quantify what the exact effects are, and then — potentially — do something about it. What we do know is that the in-flight experience does have quite an impact on us.
Planes typically fly at an altitude of 35,000 feet (10,700 metres). This high up, the air pressure is just 24.8 kPa. kPa stands for kilopascal, which is the standard unit for measuring pressure. Atmospheric pressure at sea level is typically 100 kPa, which is the same as 1,000 millibars, 0.99 atmospheres, and 14.5 pounds per square inch (psi).
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Aircraft cabins are pressurized because, at 24.8 kPa, we wouldn’t be able to breathe otherwise. But they are only partly pressurized, to the equivalent air pressure that you’d find at 8,000 feet altitude, which is about 76 kPa. The air inside the plane is much less humid than what we’re used to.
As a result, after you have spent 12 hours on a long-haul flight with reduced pressure and lower humidity, you feel some negative effects: itchy eyes, dry skin, sometimes a sore throat. I know that I don’t feel my best after two 12-hour flights with just a few hours’ break between them.
How, though, does this suboptimal environment affect the way wines taste in the air? If we think about the way we perceive wine, then we can make some guesses.
First of all, we know that environment changes flavor perception. We all bring a lot to each wine tasting. There’s our previous experience of wine. There’s our expectation — and even our mood. These feed into the complex processing that takes place in our brains to construct the conscious experience of flavor.
The lower humidity and pressure in an air cabin changes the way the olfactory receptors at the back of our noses interact with smell molecules. The transport of these smell molecules to the receptors is reduced because of the lowered air flow, much as happens when we have a cold or an allergy. This reduces our ability to smell.
Because what we think of as taste is strongly connected to smell, we’re likely to experience airline food and drink as less intense. The drying out of our noses and throats likely exaggerates this effect. But could the real story be more nuanced and interesting than simply a diminished experience of food and drink in the air?
Scientists at a research facility in Germany have been investigating this directly and are working with German airline Lufthansa to improve the in-flight experience. The Fraunhofer Test Flight Facility near Munich consists of a 52-foot section of a wide-body Airbus A310-200 suspended inside a low-pressure chamber. Lufthansa’s researchers have used it at least six times in hopes of fine-tuning the airline’s food and drink offerings.
It has also been used to analyze the effects of flying on our perception of flavor overall, at a more theoretical level. Back in 2008 Florian Mayer and a team of colleagues compared the responses to a range of odors, tastes, and six different wines at normal pressure (95 kPa) and simulated flight conditions (76 kPa, low humidity, plus some vibration and noise).
First, they looked at detection thresholds for a range of odors. This is done with triangle tests: Scientists provide three samples, one with a particular concentration of a chemical, and two blanks without. If you can spot the odd one out, you are successfully detecting the odor or taste. Then, its concentration is gradually reduced until you can’t.
Using this technique, the scientists were able to determine that their test subjects showed reduced thresholds for odor detection in the simulated cabin environment. What’s interesting is that not all smells and tastes were equally affected. Fruity-smelling esters were perceived as much less intense in “the air,” whereas vanilla-like lactone aromas were far less affected. Most significantly, the perceived intensity of sweet and salty flavors fell by as much as 30 percent.
When it came to comparing wines, the researchers did the experiment with highly rated examples of red and white, but also put in cheap supermarket wines. The preferences didn’t change — people still preferred the more expensive wines in “the air” — but overall the wines tasted less fruity and thinner, so lighter-style wines suffered more than big, bold, full-flavored ones.
Of course, it’s not just pressure and humidity that are different in the air. There’s also the background noise from the engines. It is becoming clear that noise affects the way we perceive flavor. Researchers believe there is a definite cross-modal effect, where one sense impacts another, between sound and taste.
A study in 2011 showed that loud white noise significantly reduced the experience of sweetness and saltiness. The background noise in flight averages 85 decibels and, as with altitude and cabin pressure, that degree of sound doesn’t affect all flavors equally.
Professor Charles Spence and his colleagues have pointed out that the taste of umami is unaffected (and even enhanced) by background noise. They speculate that this is why in the air people love ordering tomato juice and Bloody Marys even if they never do on the ground. Spence speculates that airline passengers might have worked out by trial and error what scientists have only recently figured out: Rich in umami, tomato juice tastes better with background noise than it does without, and umami-rich foods don’t suffer from the same altitude and humidity effects that diminish other flavors.
As a result of these sorts of studies, airlines are now routinely enhancing the saltiness and sweetness of their meals, adding extra spice to offset the effects of the cabin environment.
The wine piece, however, remains unknown. Does it really taste so bad in the air? Should we be changing our preferences and ordering wines that wouldn’t suit our palates on the ground?
This is where we run into some complexity. A lot of the pleasure of drinking wine doesn’t just come from the liquid in the glass. I actually enjoy the experience of flying: There’s a buzz to hanging around airports, getting into the air, and heading to a new destination. I’m likely to enjoy any wine that’s poured into my glass.
Speaking of: Glasses are another factor beyond our control in aircraft cabins. Airlines can’t afford the space to store fancy glasses for premium passengers, and those in the back of the plane will be drinking out of plastic. And we know that glassware affects perception.
For those who find flying stressful, doing anything, including drinking wine, will be less enjoyable in the air. If I’m sitting in the back of the plane, as often is the case, then the wine options will be very limited, and wine will be reduced to a commodity: red or white, and rarely more than just drinkable. In that case, whether or not I’m getting it at its best is a moot point. If I’m flying business class, I’m usually so happy to be out of economy that I’ll love anything I’m poured.
If we begin to factor these elements into the equation, plus of course individual differences, then suddenly the matrix of any study seriously assessing wine in the sky becomes impossibly complicated.
How, then, can we make flying less of an ordeal for our senses? We might never be able to completely normalize air pressure and humidity levels in the cabin. The problem is, as the pressure inside the cabin increases, so does the differential between inside and outside the plane. This puts more stress on the hull, and repeated cycles of taking off and landing increase metal fatigue.
This is also one of the problems of humidity. The vast temperature differences inside and outside the vessel cause issues with condensation at altitude. This can shorten the hull’s lifespan and cause corrosion. Newer planes, notably the Airbus A350 and the Boeing 787, have hulls mostly composed of carbon fiber composite, and they can operate at slightly lower pressure, equivalent to 6,000 feet rather than the usual 8,000. They also have on-board humidifiers. Studies have shown that increasing pressure a little like this has meaningful improvements, but little is gained by increasing it further.
I am old enough to have flown from London to Melbourne on an Olympic Airways plane (the cheapest option) when there was still a smoking section. There was no video-on-demand, and the flight was smelly, noisy, and seemed interminable. All in all, long-haul flying is now much better than it was as recently as the mid-1990s.
The experience on a new, modern plane has improved to the point that onboard food and wine seem to taste, if not particularly great, much better. That’s because the experience of flying is so much more tolerable.
My best Champagne experience last year was drinking Veuve Clicquot with some fellow travelers at the bar at the back of the top deck on an Emirates A380.
It’s not all about the liquid in the glass — or even diminishing perceptions at 35,000 feet. Sometimes, wine is so much more than just wine.