Microbiology is also the main reason why cheese is so yummy; in fact if we didn’t add microbiology we wouldn’t have any cheese at all. Microorganisms are instrumental in the cheese making process.
How is cheese made?
The basic cheese making process goes like this:
- Warm some milk (pretty much any milk will do as long as it hasn’t been ultra-pasteurised UHT or heated to a high temperature)
- Add a starter culture of bacteria such as Lactococcus lactis, Lactobacillus helveticus or Lactobacillus delbrueckii
- Allow time for the bacteria to ferment the lactate producing lactic acid
- Add rennet (an enzyme that coagulates milk to produce curds)
- Allow time for the curds to set
- Cut the curds into small pieces allowing them to separate from the whey (watery liquid left behind P.S. can be “recycled” into ricotta!)
- Drain the curds, breaking them up into bits then add salt
- Press (remove further excess whey/water from the curds)
- Wax or leave in a cave to age (dark, damp, humid… a bit like my office and my socks!)
- Wait for the cheese to mature (at least a couple of months but 1-2 years is even better)
Essentially it’s the acidification with bacteria which produces lactic acid that makes cheese. These days bought starters are numerous allowing cheese makers (including ECIC) to make many different cheese varieties, but in the past the acidification was caused by the natural bacteria present in the raw unpasteurised milk.
The acidification and salt levels also control the types of organisms that can grow on or in the cheese during maturation which affects the flavour and consistency of the cheese. The process is alchemy, not science.
This basic method would give a typical hard cheese like farmhouse crumbly cheddar, but for more fancy cheeses other microorganisms are added:
- Roquefort, Stilton – Penicillium roqueforti is added to the surface of the cheese and then pushed in with a spike during the maturation process to give the characteristic greeny blue swirls of blue chesses as well as their strong flavour
- Camembert, Brie – in order to get the white fluffy mould growing on the outside of these cheeses two types of fungi are added, Geotrichum candidum and Penicillium candidum. P. candidum also neutralises the acidity in this type of cheese and helps give a milder flavour
- Limburger, Port-du-Salut – Brevibacterium linens is a red bacterium that gives these cheeses their characteristic colour as well as their distinctive smell, like smelly feet… and this is because it’s the same bacterium that actually causes smelly feet! Still want to eat smelly cheese? Ewww!!
- Emmental – the holes in this classic Swiss cheese are actually caused by the deliberate “infection” of the cheese by Propionibacterium spp., an anaerobic bacterium that produces propionic acid and hence CO2 inside the maturing cheese forming large bubbles of gas (the holes)
The traditional method of storing cheese as it matures is in caves; ECIC has a second-hand wine chiller that has been converted into her “cheese cave” and it works brilliantly.
In caves the cheese becomes covered in a “rind of microorganisms” that helps develop the flavour of the cheese. Many cheese makers insist their specific cave location and its specific microorganisms are what give their cheese the unique taste. However apparently it’s more to do with cheese being made in the same way not the area in which the cheese was made. So a cheese made to the same recipe and method in France, Australia and Canada would have the same microbiome and hence pretty much the same rind and taste.
However if a cheese has a regional name e.g. Roquefort or Swaledale, then even though it tastes the same it should only be called Roquefort or Swaledale if it is made in Roquefort in France or Swaledale in North Yorkshire. Cheddar doesn’t have protected status even though it was first in Cheddar, UK, probably because the process of turning the curds is actually called cheddaring... or maybe the name cheddar is just too commercially important.
Some cheese making is extreme even for my microbiologically harden senses.
Cheese mites, yep… what the heck are cheese mites!? Tyrophagus casei or cheese mites are tiny insects that feed on cheese or the microorganisms growing on cheese. This mite (I mean…might) sound disgusting but some cheese makers actually cultivate mites on their cheese in order to get the desired flavours; and yes if you are wondering… you do actually eat the mites!!!! Such cheeses include Mimolette and Cantal… OMG I think I’ve eaten Mimolette… no one told me about the mites!!!
In fact cheese mites have been known about for over a hundred years, and were the subject of a 1903 silent film “Unseen World” but perhaps this video is more illuminating!? I think I feel sick…
What can microbiologically go wrong with cheese?
So cheese making is simple… but there are lots of ways it can go wrong. If your milk becomes contaminated it can really mess up cheese making.
- Contamination with a Lactobacillus spp. phage - the phage (a virus against bacteria) kills the wanted Lactobacillus spp. bacterium before it acidifies the milk, preventing the cheese from forming.
- Contamination with Pseudomonas spp. apparently occurred to a company in Ireland leading to the bacterium killing off the wanted Geotrichum spp. which prevented rind formation. It took a while for them to identify the milk storage area as the source.
There are other microorganisms of concern to the cheese making industry too; those that would make the customer sick. The classic infections that can be acquired from dairy products include listeriosis, brucellosis, Mycobacterium bovis infection as well as toxin mediated forms of “cheese poisoning” e.g. Enterotoxigenic Escherichia coli or Staphylococcus aureus.
The use of pasteurised milk and raw milk from reputable sources as well as careful attention to food hygiene should prevent these infections however it is highly recommended that pregnant women and the immunosuppressed should avoid unpasteurised milk products. Needless to say if contamination happens at a major cheese manufacturer then it would cause serious damage to their finances and reputation, so cheese makers take special care of their milk, starters and cleanliness.
So cheese making really is a lesson in microbiology, and in fact cheese makers are essentially “microorganism farmers”.
Now where did the ECIC go, maybe she’s making me some supper… it mite be cheese on toast…