examination of microbial tolerance to ethanol

This is a myth that is repeatedly discussed many many times, with several links citing each other.

The principle is that in (generic) Medieval (generic) Europe, due to (generic) contamination in the water, it was safer somehow to drink (generic) alcoholic beverages than it was to drink well water, (potentially due to cholera etc).

The links above discuss several problems with this myth (more thoroughly discussed by Squatriti 1998), all arguing that they still drank water because:

• water was free
• beer and wine were expensive
• mountain spring water or well water was widely consumed, and was usually managed in larger cities
• it was already known that water could be made potable by boiling

Nevermind that Europe contains many places that are not the same, and not all alcoholic beverages are the same.

Some points are not brought up:

• the alcohol percentage of beer is insufficient to purify the water
• beer production often involves a long boiling step, which would actually be responsible for sterilizing the water
• the percentage in wine is likely sufficient, but wine is not made from well water, so it is unlikely to be contaminated in the first place

Showing data from Ingram 1990, three different species are examined in the context of growth at varied concentrations of EtOH: Escherichia coli, Zymomonas mobilis, and Lactobacillus heterohiochii (appears to be a synonym of Fructilactobacillus fructivorans ).

Beer-strength levels of alcohol are not effective on the three species examined. These are not pathogens, but nonetheless show substantial variability in alcohol tolerance. Zymomonas itself can produce alcohol, so naturally would have a high tolerance.

For comparison, the CDC recommends use of chlorine for treatment of pathogens in water (including bacteria, virus, and protist), noting that single-digit ppm concentrations of chlorine are often sufficient to purify water.