After explaining to others why beer isn't vegan, some will often question the suitability of yeast. Is this single cell organism with the ability to reproduce a valid reason for vegans not to drink beer?
Yeast are eukaryotic microorganisms classified as part of the fungi kingdom. Neither animal or plant, yeast are a different concern altogether.
Brewers crudely describe the vital role that yeast plays in the brewing process with Nobby's Brewery clearly summarising it on Twitter: "Yeast is ALIVE, it had sex, ate sugar and peed alcohol in your beer." Just as long as the temperatures and conditions are right they will keep going until every last trace of fermentable sugar has been devoured.