As the weather starts warming and beer gardens start regaining their lingering crowds and backyard barbecues become weekly things, let's not judge the lone man sporting a beer koozie on his beer can; science is on his side.
A study published in Physics Today looks at the importance of condensation when it comes to beer warming, finding that condensation actually affects beer temperature more than the temperature of the outside air.
Author Dale Durran notes that latent heat, or the energy and warming that occurs when water changes to liquid form, may actually warm your drink more. When your beer can becomes covered with condensation, all the energy from the water droplets (the latent heat) gets transferred to the beer inside the can.
When running tests, Durran and his students found that the more humid an area was, the more the beer responded to latent heat. When kept at 95 degrees Fahrenheit and at a humidity greater than 60 percent, the temperature increase due to latent heat was far greater than the changes due to the hot air. "I was surprised to think that such a tiny film of water could cause that much warming," Durran said.
As the outside of the can warms, however, the amount of heating from condensation decreases, probably because the water in the air no longer forms water droplets when it hits the aluminum. So the trick? Stopping the condensation in the first place, which then keeps the aluminum can fairly cold, and the beer inside colder. "Probably the most important thing a beer koozie does is not simply insulate the can, but keep condensation from forming on the outside of it," Durran told the University of Washington. So don't judge the guy holding his beer in those silly-looking sweaters; you're the one drinking warm beer.