I have seen that when preparing coffee without milk(just water and coffe), soluble coffe (at least Nespresso one) foams when stiring it just a bit. However, not soluble coffe does not.

Does someone know the reason?

I have seen that when preparing coffee without milk  (just water and coffee), instant coffee (at least Nespresso) foams when stirring it just a bit. However, regular coffee grounds do not.

Does someone know the reason for this?