The perfect department has yet to exist, and legitimate reasons for complaints do occur. Taking responsibility for obvious mistakes or oversights can show the individual that you are concerned about correcting the problem. Denials should be saved for complaints that have no factual basis. Responsibility for the entire department is just one item on the CDM's job description that we all learn to accept at the inconvenient times. Keep a written complaint log.
Most facilities have a process for formally handling complaints of all types.
The dietary department should also have a standard operating procedure for handling concerns. A simple complaint form listing the resident or family member's name, the date, the basic complaint, and the actions taken to resolve the problem should be sufficient. This can be developed into a great tool to refer to when future complaints arise, or to demonstrate patterns of problems. The items listed on the complaint log should also be an endless source of quality assurance studies. Leave with clear goals established.