US scientists and health experts advise passengers to limit alcohol, especially cocktails containing artificial sweeteners. A flight attendant, speaking to Travel + Leisure magazine on 17/7, suggested adding diet coke to this list. The reason isn't health risks or negative flight effects, but simply that flight attendants find it frustrating to pour due to excessive foam.
"Ordering diet coke on a plane is one of the most irritating requests for flight attendants", said flight attendant Luke Gary. When pouring, they must fill the cup and wait approximately 60 seconds for the foam to dissipate, even though the liquid content is less than one-quarter of a cup.
Flight attendants then repeat the pouring and waiting process, often attempting conversation with passengers. However, most passengers have their headphones on and prefer not to chat. "What am I supposed to do during that one minute of waiting? Just stand there awkwardly?", Gary questioned.
Gary's frustration is rooted in a scientifically proven fact: diet soft drinks foam more than regular sodas. This becomes particularly evident as attendants pour dozens of cans on every flight.
An article from McGill University (Canada), published in 2022, explains that a soft drink's effervescence depends on how easily CO2 bubbles form within the liquid. More easily formed bubbles result in more intense foaming.
Bubble formation is primarily governed by two liquid properties: surface tension and viscosity.
"When a liquid has high surface tension, its molecular bonds are strong", the report explained. This allows some spiders to move across water, as their weight is insufficient to break these molecular bonds. Liquids with high surface tension make bubble formation difficult.
Diet coke, conversely, has low surface tension. Its formula contains surfactants such as aspartame and potassium benzoate (a preservative), which facilitate more CO2 bubbles forming and escaping to the surface.
Viscosity also impacts foam levels. High-viscosity liquids typically produce fewer bubbles, but these bubbles persist longer once formed.
While many passengers find their preferred diet soft drink worth the wait, even if it adds to flight attendants' impatience, attendants offer a practical alternative. They recommend choosing simpler beverages, particularly bottled mineral or spring water poured directly from the bottle. Passengers can also bring their own purchased water bottles or fill them at the airport before boarding, if it's not essential to have a diet soda.
Anh Minh (Via T+L)
