When are you really dead?

Often when discussing beginning of life issues ensoulment is brought into the debate. It is not often that we hear about desoulment. The point at which a person dies is the point at which the soul is separated from the body. Christ died when he released his spirit. When does desoulment take place? Is it at brain death? Is it some period of time after brain death? Is it when our heart stops beating? Do we know for certainty this answer?

Traditionally in medicine, a person was considered dead when he was "cold blue and stiff", but organs cannot be harvested from these patients. The sermon at Audio Sancto titled: May We Donate Our Organs contains some interesting insight on how the definition of death has been pushed to ensure viable organ harvest.