It is Sunnah to use right hand at all time. As reported by 'Umar bin Abi Salama: "My hands will usually surround the plates when eating, then Allah's Messenger said to me," Call upon the name of Allah and eat with your right hands and eat from the dishes nearest to you ". 'Aishah r.a. also has narrated that the Prophet s.a.w likes to start something from the right.

But if doing so will cause inconvenience to other people, such as staining the spoon and cup, then there's nothing wrong with using the left hand.