How quickly does ground coffee get stale? On this website I found this claim:


  Great baristas in fact will only grind beans for an espresso right
  before using them. 30 seconds after they have been ground, the beans
  are already too stale for a good espresso.


I am deeply skeptical. Is there any way to verify, quantify, or otherwise substantiate that claim, or is it superstition?
I can say, by experience, that it's not a superstition. Maybe not seconds, but for sure it's just a few minutes.

Maybe someone could find a reference to an experiment or I may encounter and add it later. But, you can easily observe it by your nose.

The aromatic components are the source of the flavor in coffee beans. When you ground them, you crack them fine. The components get free and start to evaporate. That's why you can smell them. However, we want to taste them so badly. So, we need to trap then into the water as quick as possible, before most of them evaporate.



Below is a nice chart that shows how quickly coffee goes stale when it's stored as whole beans. Ground coffee, I assume, would be similar, but so much quicker as the surface area is greater for evaporation this time.

When does coffee go off?