Why it is easier to spill your coffee than your beer this Christmas?

Celebrations for this Christmas and New Year will be sure to fill restaurants, bars and cafes as these places serve as areas for reunions or just to take a break and catch up with friends and family. 

The staff at these establishments will be busier than usual as they carry yours and your friend's full drinks to your table.  You think this is easy?  It's actually considered treacherous!

If you ask anyone who has had the experience of carrying coffee through a very busy café, they will tell you that spilling drinks on the sides of the cups is really easy.  But carrying beer – even if you have had one too many….. is so much easier! 

Scientists think they know why, and it’s all to do with the beer’s foamy head!

Researchers have recently studied the waves created by people carrying different drinks to demonstrate that foam reduces sloshing, and dampens the waves themselves.  This knowledge could one day be used to work out better ways of transporting huge quantities of liquid more safely and efficiently. 

Using a high speed camera, the study set out to prove that coffee is tricky to carry, whereas beer is so much easier. 

It filmed a moving stage and fluid with, and without a head of foam, and the creation of sudden movement.  The research showed that just a few layers of bubbles are all that is needed for the effect to work, and it doesn’t matter if it is foam on a pint of Guinness or Heineken – it reduces the sloshing and is very efficient at damping the waves. 

The foam is efficient because of viscous dissipation where the ‘thickness’ or viscosity of a fluid takes energy from its motion and transforms it into heat energy.  As the waves form and the beer travels, the foam on the beer rubs against the walls of the glasses, and this rubbing causes a lot of energy, which results in damping. 

The effect is not seen in cups of coffee, which do not have any foam on top of them.  That's why coffee spills more easily than beer.

To conclude, the more foam a drink contains, the less likely it is to slosh around. 

Although the liquid used for this study was beer, this study could one day be the way to help create better ways of transporting large quantities of liquid with more safety. This should be applied more to industrial loads in the form of cargo.

So, this festive period when you are crossing a busy room with a few beers in your hand, trying not to drop them – be thankful that it’s not hot coffees you are carrying!