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The Sound Of Coffee

Friday, July 10, 2015

Do you ever find that a good coffee just seems to sing to you?

Well, you’re not the only one, and you’re certainly not imagining it!

Indeed, there’s more to coffee than meets the eye, it’s not just about caffeine, silky aromas, delicious taste sensations and latte art.

Yes, when you pour that magical cuppa, numerous chemical reactions are taking place behind the scenes, and it’s simple physics at play behind the ‘sound of coffee’.


Sound Waves and Coffee

When you stir a coffee – let’s say in this case a Vienna Coffee, for example - the creamy layer separates back out, and you will hear a ‘tapping’ sound from the liquid which will get higher and higher in pitch.

This is caused by the fact that sound travels at different speeds in both liquids and gas.

The speed of sound is higher in water than it is in air as the water molecules are much closer together.

The shock waves that create sound travel faster through close-packed molecules, so sound is faster in liquid coffee than in froth, and faster sound waves have a higher pitch.

Thus, when you mix froth and liquid — for instance, by stirring whipped cream through a coffee — you affect the speed of sound in the drink.

So, by introducing air bubbles which slow the speed of sound, you get a lower pitch noise from your cup of coffee.

But after stirring, the cream separates out and rises up.

When you keep tapping the bottom of the cup, there is less and less gassy whipped cream down low, so the sound can move more and more quickly, and the pitch rises.

So you can hear that crescendo of increasing pitch as you just tap the bottom and let the foam rise to the top.

You can hear the opposite happen next time your barista is frothing milk with an espresso machine – that is, an initial squealing sound.

However, as the milk gets whipped into a warm froth, the pitch will drop lower and lower.

Over to you

Does your Cafe2U coffee sing to you?

Do you know any other amazing scientific facts about coffee?

As always, get in touch with us here at the Cafe2U blog with your comments and questions – we love hearing what you guys have to say!

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