[![blood for drinking][1]][1]

  [1]: https://i.stack.imgur.com/USq0O.jpg

Many cultures drink the blood of livestock.  Currently the Maasai are the ones famous for it, but horsemen throughout history drink the blood of their horses.  If you have big tame animals around it makes sense.  Blood is sterile when it comes out.  The animals can spare you some now and then in exchange for your good care and concern.  Blood is very nutritious.  Plus as opposed to milk, male animals can contribute too.

However, microbes that do some other reaction are acceptable. 
**no need.**

Just as beer can be made in almost any part of the world, the replacement beverage must be easily producible worldwide, with Neolithic technology.
**you can bleed an animal with a sharp rock.**

Just as beer resists spoilage, the replacement beverage must have some sort of chemical makeup that keeps it germ-free relative to pure water.
**The immune system of the animal keeps it germ free.**

Just like beer, it must be palatable to humans. Acquired tastes will make it delicious.

from above source
> I know I'm looking kind of bug-eyed in these photos, but it actually
> wasn't that bad. It was very thin and bland. It tasted just like human
> blood. (Not that I'm in the habit of drinking human blood. But if
> you've ever cut your lip or had a tooth bleed, you know the taste).
> There was actually very little taste as I was drinking it, but for
> several minutes afterwards I had strong blood aftertaste.