You get lactic acid bacteria in wine and cider when you mature it. If you drink kefir after a heavy night usually you feel much better and that's full of labs and and yeast too. Going have to see if it's in beer too.... persumably it is,  especially if it's coming from a bottle because it lasts longer in a crown capped bottle.

 Definitely feel a difference the next day between the living and pasteurised mass produced stuff.