Compared to ancient beer the yeast of modern beer is killed off before bottling, so you can't use it as a yeast replacement, but instead this allows the beer to be stored for a long time.
'Killed off'? Or just filtered? (Genuine question - I brew a bit, and have used mine for bread, but don't really know anything about commercial brewing.)
I'm just a home gamer so could be wrong. In large commercial breweries it is killed off, flocculated out with a flocculation agent then filtered out. It is killed at a certain time so the amount of remaining sugar is controlled.
Some microbrews don't do this and you can recuperate live yeast from those beers for brewing or baking.
I've always heard filtered to bring it to sterility, but there have to be other steps to flocculate. Micro brews or traditional European brews are often bottle finished.
Some micro breweries use a finishing yeast that's different than the fermentation yeast to keep that proprietary. I think anchor brewing comes to mind for this.
