Physics and chemistry in the kitchen and when cooking are nothing new, but physics when drinking coffee or even more clearly when drinking cappuccino are for us. Actually, enjoying a good cappuccino should above all relax, but relaxed learns and teaches it better. So welcome to lesson 1 in coffee physics. Today: The cappuccino effect. The situation is as follows: If you stir a cappuccino and then tap the bottom of the cup with the spoon at intervals that are not too large and not too small, you can hear very clearly how the resulting sound is very muffled when you first tap it and deep, but builds up to a very high pitch until the last knock. Why is that?
There were first scientific discussions on this topic as early as the late 1960s, and the cappuccino effect can be perceived so quickly and is presented so often by accident that so many cappuccino drinkers have noticed it all over the world and, of course, above all in internet forums about it was discussed. The explanations for this effect are as diverse as, of course, largely wrong. The correct explanation for this phenomenon, which incidentally also occurs with tea with sugar or milk with cocoa, is of course served here with us. The excessive milk froth in a good cappuccino is to blame for the change in the sound of the spoon tapping.
The sound travels more slowly through the air than through liquid, thanks to the frothed and stirred milk froth. A slow sound means a deep tone and the high tone can only be heard again when the air bubbles are slowly removed from the liquid and have settled in their milk froth crown. This also explains why the sound only slowly returns to its normal level.
