system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If bacteria produce ethanol through fermentation, and ethanol can kill bacteria, why are they not killing themselves with their own ethanol?
gpt
Bacteria does not produce alcohol. Fungi called yeast produces alcohol. 


However, your point remains true, alcohol still kills yeast. It's all about concentration. Beers and wine can be produced by yeast, up until about 15%. Past there, it kills the yeast. To make a harder alcohol, you have to distill (basically purify by boiling) the alcohol yeast produces. 


Why does yeast produce a substance that kills it? Well, because it's a waste product. It's exactly equivalent to asking why a large concentration of CO2 or urine will kill you. Because it's waste you are try it dispell, and if unsuccessful, it will kill you.