Today’s upsetting cheese-related news concerns a batch of goat cheese sold by London artisanal

Today’s upsetting cheese-related news concerns a batch of goat cheese sold by London artisanal cheese maker Neal’s Yard Dairy. Due to harmful bacteria–Listeria–in the cheese, it’s been recalled. Listeria can cause flu-like symptoms, such as fever, muscle pain, chills, nausea, and diarrhea, as well as lead to meningitis.

But, as we know, all cheese is full of bacteria, of course! So let’s use this news report as an excuse to discuss how our favorite topic, microbes, relates to cheese.

Eating cheese is essentially an exercise in smelling, tasting, and feeling the effects that bacteria make on milk. Some think that cheese was invented by accident thousands of years ago when men would transport milk in the internal organs of animals - the shaking of the milk combined with the bacteria naturally found within animals’ stomachs created a primitive version of cheese. Without bacteria, cheese would be bland and uninteresting. However, this doesn’t mean that cheese makers don’t need to be careful in keeping the bad bacteria out while inviting the good bacteria in to ripen and flavor their cheese.

Only a few types of bacteria are used for most modern cheeses, though many say that traditional cheeses are more interesting and flavorful because of the greater variety of bacteria they use. According to Serious Eats, today, the bacteria most often used in cheese come in five kinds: lactic acid bacteria, which keep out bad bacteria, ripen the cheese and add flavor; propionic acid bacteria, which digest the acetic acid and produce propionic acid and carbon dioxide (where the holes in Swiss cheese come from); blue molds that grow in the small cracks within ripening cheese like Roquefort; white molds that grow outside many soft cheeses like Camembert, creating ripe outer layers; and smear bacteria, which add the stinky, almost rotten, characteristic of cheeses like Müenster.

And what about the bad bacteria? CurdNerd explains how harmful bacteria can find their way into a cheese if its environment is unclean or has poor air circulation, the cheese is not perfectly dry, it has been left sitting in whey, it has been cross contaminated between cheeses, or if it hasn’t been salted properly. Many of the bad molds can be removed without sacrificing the whole cheese while the cheese is still being made, but if your cheese starts growing something fuzzy at home, it’s probably best to just throw it out instead of sampling your new bacteria!

Want to learn more about the microbiology of cheese? Check out this video from The American Society For Microbiology, or click on any of the links above!