Today, there are more options than ever for what you can order to drink at 30,000 feet. A look at a typical in-flight menu shows everything from soda, tomato juice, and tea to flavored sparkling water, cold-brewed coffee, and canned cocktails on offer. Most of the time, your choice of beverage makes little difference to your cabin crew. But there’s one popular option many flight attendants wish you wouldn’t order, and it probably isn’t for the reason you’re expecting.

A Bit Too Bubbly

As one of the most popular soft drinks in the world, Diet Coke is the go-to for countless air travelers every day. Unfortunately, it’s also many flight attendants’ least favorite beverage to pour, according to a recent story from Travel + Leisure. “People ordering Diet Coke in the air is one of the most frustrating experiences as a flight attendant, because when you pour the Diet Coke, you pour it all the way to the top,” flight attendant Luke Gary shared with the outlet.

The problem, Gary explained, is that “the bubbles take literally 60 seconds to dissipate before you even get one-fourth of a cup. And then you have to keep pouring it on, keep pouring it on, trying to make conversation with the person.” It can get awkward.

Indeed, diet sodas are fizzier than their sugary counterparts. This includes soft drinks other than Diet Coke, but Diet Coke poses the biggest problem because it’s more popular than its competitors. That usually doesn’t make much of a difference when you’re pouring one just for yourself — and it matters even less when you’re drinking it straight from the can. But when it’s your job to serve dozens of passengers their drinks as quickly as possible, those extra minutes quickly add up.

Science Explains It

It turns out there’s a scientific explanation for the fizziness. As author Ada McVean explained in an article for McGill University, diet soda is fizzier than sugary soda due to differences in surface tension and viscosity. Ingredients such as aspartame “decrease the surface tension of a liquid,” which makes it “a bit easier for bubbles to form,” and the viscosity of diet soda allows those bubbles to rise and escape the liquid more quickly. Full-sugar sodas, on the other hand, tend to slow the movement of bubbles to the surface. All of this is exacerbated on a plane, with lower cabin pressure at high altitudes making bubbly drinks especially fizzy. 

Ordering a Diet Coke is hardly the only drink-related mistake you can make at cruising altitude, though — and not just for reasons related to being courteous to cabin crew.

Coffee and tea are less than ideal because they’re made from the plane’s tap water, the tanks of which may not be cleaned as often as is ideal. On the other hand, alcohol is especially dehydrating while flying, and soda — diet or otherwise — can cause more bloating than at sea level due to air cavities in your body expanding once you reach 8,000 feet. That’s no reason not to treat yourself the next time you’re stuck in the middle seat, but you may want to keep this info in mind when placing your drink order.

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