Do we know what the Klingon Bloodwine is actually made of? Is it actually as the name suggests? or is it just referring to the colour of it?
It's never made clear in the on-screen canon, but according to the Star Trek Cookbook (by Ethan Phillips and William J. Birnes):
"Klingon bloodwine is exactly what it says it is: fermented blood and sugar."
There's been a lot of speculation among fans as to how one is supposed to interpret Worf's quote:
"I like my bloodwine very young, and very sweet."
Blood of their enemies and sugar
TNG writer Ronald D. Moore (responsible for much of the Klingon arc in TNG) was asked this question today at the Star Trek 50th Anniversary Celebration in Las Vegas.
MOORE: The blood of their enemies. And it would be really, really sweet. They like it sweet. So blood with a lot of sugar.
In Star Trek: Deep Space Nine Martok boasts that he has a barrel of 2309 bloodwine and that there is no finer "vintage". "Vintage" when used to refer to wine implies grapes or at least something that grows in a vineyard. So I don't think bloodwine contains blood any more than sangria contains sangre.