Cow’s milk is about 90% water. It also contains a sugar called lactose, as well as vitamins, minerals and enzymes. However, the most important constituents for us cheese makers to be aware of are the proteins and fats, which each make up between 3% and 4% of raw milk (i.e. straight from the cow).
There are many proteins in milk but caseins are the ones crucial to the act of making cheese. As milk becomes more acidic (for example, by adding lemon juice or a bacterial culture) the caseins precipitate out of solution, and start to become solid, or clot. These clots trap within them some water but, crucially, some of the fats too. We call these protein/water/fat clots curds, so casein clotting is the very essence of cheese making, as it is how we cause the clotting and then treat the formed curds that determines the character of our cheese.
With this appreciation of how cheese is created from milk, it’s easy to understand why higher fat milk will yield more curds that lower fat and, for that reason, why most cheese recipes call for full fat milk, rather than semi-skimmed or skimmed which both have less fat available to make cheese with.
When it comes to buying milk though, the amount of fat within it is only part of the consideration. Firstly, all shop bought milk in the UK has to be pasteurised. Milk is an excellent medium for growing bacteria in, which makes it very quick to spoil unless treated. Pasteurisation is a process designed to increase the shelf life of milk by reducing the number of bacteria within it. Raw milk is heated to 72C for 15 seconds, this kills the majority of bacteria (though not all) whilst leaving the milk with most of its original structure, although it does reduce the naturally present calcium. Pasteurised milk is great for homemade cheese but your recipe may call for added calcium chloride to produce firmer curds.
UHT or ultra-heat treated milk is raised to a temperature above boiling point. Whilst this kills all the bacteria and means the milk can be kept out of the fridge almost indefinitely, it also spells the end for it as a cheese making ingredient. The chemistry of UHT milk is so radically different from raw milk that it just will not form curds and cannot be used to make cheese.
Another milk treatment that affects how we make cheese at home is called homogenisation. This process creates a standard product for the consumer. Milk from many cows and dairies is mixed together in huge vats before being forced at very high pressure through an incredibly small nozzle. What comes out is milk that is very consistent, i.e. same taste, whiteness, fat content, etc in each bottle. However, what also happens is that the fat globules are reduced in size, by as much as 500-fold which is bad news for making cheese at home. With very small fat globules it becomes almost impossible to achieve a solid curd and yields are very much reduced as the fat stays in suspension rather than getting trapped in the casein clots.
You may not have ever noticed before, but virtually all milk sold in the UK is homogenised, leaving us with few choices of off the shelf milk we can productively use.
So, quite a bit of information there, where does it all leave us? Well, in summary:
The obvious remaining question then is: where can I buy unhomogonised milk to make cheese at home? Happily, there are some options that should be convenient for most people. The ones I know of are below:
Asda Gold Top is homogenised, and Sainsbury and Morrison don’t appear to sell any Gold Top.
You may also know of a local producer where you can get milk, or perhaps you are one and would like to share with our community your product. If so, get in touch with me on Jack@homemadecheese.org and let’s share this knowledge.
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