I told her this... I was pretty sure no pathogens could exist in wine, because it's high alcohol content... I wasn't so sure about beer, which can be 3ish percent or lower and still qualify as "beer". As far as the yeast making other chemicals or other chemicals being produced somehow, I am not sure. I'm too new at this to dispel all her fears. She said yeast can also produce methanol, which I think is a poison... but that doesn't sound right to me.
If she wants to be an idiot who only believes what she wants to believe AND wants to make decisions based on a limited understanding of things, then that means more beer and wine for you and folks who understand or want to understand the truth about things. Not their own unfounded ignorance.
Methanol is produced at an extremely low level, and it will be diluted. Distillation is a concentration of ethanol and methanol, which is why in distillation (including freeze distillation) it is a dangerous factor, but with the dilution in any brewed drink, even up to 18%+abv, it'll be fine. You'd be more likely to have alcohol poisoning before you would have a methanol problem.
It's not an issue due to the low methanol % compared to the much higher ethanol %. Your liver is too busy metabolizing the ethanol, thus allowing the methanol to safely pass through your system.
Distilling completely seperates the methanol from ethanol which is why it becomes a concern. The first X amount out of a still is nearly pure methanol, which gets collected seperately and discarded. It's just that some moonshiners saw that as throwing away profit, and people died as a result.
We make beer, wine mead and cider EXACTLY the same way commercial breweries, wineries, meaderies, etc do, except simply on a smaller scale. We use EXACTLY the same ingredients, and process.
The same yeast as well.
If she's that worried, then she needs to quit drinking booze of ANY kind...because she's running EXACTLY the same risk with her wine coolers and whatever else she likes to drink from the big guys as does with yours. The same amount of methanol in proportion to the size of the batch is produced at Budweiser St. Louis as in your brewery. The same amount is produced proportionally in the vats in Napa Valley or the Rhine region of Germany as is produced in your basement in those 5 gallon buckets of wine.....
*shrug*