A flight attendant in Canada, identified as Jet and quoted by the Travel + Leisure blog, revealed that Diet Coke is one of the most complicated drinks to serve during a flight. This enumeration, although popular in the United States and similar to the light or zero versions available in Portugal, requires more time and patience from the cabin crew.
The difficulty is not related to the taste or the brand, but rather to the amount of foam the drink produces. When a can of soda is opened and poured inside a plane, the cabin pressure, which corresponds approximately to that found between 7,000 and 8,000 feet of altitude, causes the carbonated drink to release more bubbles than would happen on the ground. In the case of Diet Coke, this effect is more pronounced, requiring the crew to pour the contents gradually.
According to the Office for Science and Society at McGill University, cited in the same article, Diet Coke and other sugar-free sodas produce more persistent foam due to their composition. The drink has a slightly higher viscosity than sugary sodas, a characteristic that stabilizes the bubbles and prolongs the presence of foam. The crew member may have to wait for the foam to subside before finishing filling the glass, which can delay the beverage service, especially on flights with many people or short routes.
