[header] How to make clam chowder [title] Purchase live hard-shell clams. [step] Hard-shell clams or " quahogs " like large chowder clams, littlenecks, and cherrystones should have tightly closed shells. [substeps] If you can separate the shells easily, then the clam inside is dead. 
Clams that are already dead should not be purchased or, if already purchased, should be discarded. [title] Pass a blunt knife through the two shell halves.