Yarbarah - or blood wine - is literally a wine mixed with fresh blood.
This drink is required to sustain a member of the Blood who has become demon-dead. Without it the body will eventually decay and no longer provide a sutiable container for the power of the person's mind and eventually they will become a whisper in the Darkness.
Yarbarah can be consumed both warmed or room temperature though it seems to be the preference of the consumers that the wine be warmed usually over a small flame of witchfire.
The only viable substitute for Yarbarah is actual blood.