This may sound outlandish, but I've just read this comment which states:
Beer pretty much eradicated the black death in many areas. Think it was some Belgian monk persuaded people to replace water with beer and that stopped people catching it in his area. I always think there's no wonder it was called the dark ages, everyone was off their nut and nothing ever got done lol.
Now, of course, I don't think it's worthy discussing the characterization of the Medieval period as a "dark age", since it has been debated (and arguably debunked, methinks) at length by academics. On the other hand, the comment allures to the (ongoing?) debate about if water was commonly drunk in medieval times (which probably varied across geographical, temporal and cultural boundaries anyway).
Anyway, I googled about the claim that beer helped fend off the Black Death and found these three links, which assert the monk was Saint Arnold of Soissons, whose Wikipedia article states:
One miracle tale says, at the time of an epidemic, rather than stand by while the local people fell ill from drinking water, Arnold had them consume his monastery brews. Because of this, many people in his church survived the plague.[7] This same story is also told of Arnulf or Arnold of Metz, another patron of brewers.
Only one scholarly source is provided: Gately, Iain (2009). Drink: A Cultural History of Alcohol. New York: Gotham Books. Searching for "plague" in this last link, the first result shows a paragraph that states the following about the Black Death:
[...] As the epidemic spread westward, ale was used as a prophylactic and was believed to have won some small if notable battles against it. When the Black Death appeared in Oudenburg in Belgium, Arnold, the local abbot, forced Christians do drink his brews instead of water. Survival rates were high among his congregation, and after death he was canonized. He is now the patron saint of brewers.
So, does this hold any water? Could beer/ale help diminish mortality due to bubonic plague? What about other alcoholic beverages, specially wine? Could they also help? How would any of this work anyway? I thought the bubonic plague was spread by infectious droplets.
So, prefacing - I'm not any sort of disease specialist. I am, however, most familiar with one particular myth, and I can tell you right now that the bit on the wiki page for Saint Arnold of Soissons is outright bollocks. That's because that's the classic Medieval Water Myth, which we shall disprove in a moment. One more strike against it is that, if you'll note the paragraph prior to the one you've quoted, it's all footnoted from a single online source, whose writing is surface-level at best and has no citations itself. Barring any word from an expert in the field, I'd dismiss it out of hand.
I'm also inclined to doubt the story as Gately retells it, because he appears to be telling us about Arnold of Soissons (who was indeed abbot in Oudenburg) combating the Black Death with beer...when Arnold of Soissons' dates are 1040-1087, versus the Black Death's 1346-1353. Blight's sake, Gately, pay attention. Unless we can prove that there was an abbot named Arnold in Oudenburg at the right time, I'd dismiss it out of hand.
Now, if there is in fact a story of Arnold of Soissons combating an epidemic in Oudenburg by supplying beer to the populace, that's an area for the religious history types and I'll leave them to tell it. However, I can say that any thought of beer being a safer alternative to water is the Medieval Water Myth, which we can discard. This is my main post on the matter.
It's a very common and widespread myth (anecdata shows that you can see it in just about any context, including experts in a lot of fields, including historians), but it just plain isn't true.