How do blood banks store blood without it clotting?

[JOL]

According to theory, blood may even clot without coming into contact with air,then how do the store blood in blood banks or in hospitals?

 

[mgb_phys]

The donation bags have anti-coagulent coatings.
The stored blood is often separated so the platelets (the main clotting factor) is extracted for use separately than the red blood.