Excellent question! All of the above.

^That’s definitely not sexually-virgin blood there, but it might very well be not-used-before-in-a-ritual virgin blood!

Hopefully the alcohol in it cleaned it up a bit? Maybe knowing the source is what really grossed Louis out about it, ick.

I’m not a good resource on this, but I believe it can mean all of those. In some religious rituals, it means specifically blood that has not been used in a ritual before (as in, whoever it is providing their blood has not shed blood in a previous ritual before). Drunk before? Well if it’s been drunk, it’s been used already, not sure how you’d retrieve it for another use!  

It is true that some cultures held virgins up as oracles, and kept them separated from society at large. That they were free from the mental and physical demands that come with having a sex life (I’m not agreeing necessarily, just guessing at their reasoning in a very generalized way). 

The idea that a person who has not had sex yet could be counted on to have pure blood may stem from the fact that diseases were much more mysterious long ago; lacking treatment options, people died and/or suffered terribly from sexually transmitted diseases. 

One would suppose you would want clean utensils for rituals, and clean ingredients?