A coffee or milk machine and a method of operating such a machine

A coffee machine (1) comprising a frother (2) with an outlet channel (3) for coffee and milk foam, and supply channels (5, 6, 7) for milk, air, and steam respectively, and provided with a nonreturn valve (15) to prevent a fluid in one of the 5 channels from flowing in an undesirable direction, wherein the coffee machine (1) is further provided with a clean water supply channel (8) that connects to the milk supply channel (5) with a T-junction(9) distant from the frother (2), wherein the T- junction(9) further connects to a source channel (ll) for the lO milk.