"I'm afraid I can't say whether it is or not. The Klingons are the only ones who know for certain, and they aren't inclined to share. But I can tell you that it's a good deal more potent than most Earth-based alcohols, if that helps any?"

Which doesn't say anything particularly conclusive about its composition, unfortunately. But it's an interesting point all the same, even if the only way to tell for certain whether or not it happens to be made of blood would be to hope that the Observers would happen to be kind enough to send some. And then that the limited equipment they do have would be enough to say for certain one way or another.

Which, to be perfectly honest, he rather doubts. But it's not entirely impossible, at the very least.