Its all about the calcium. Its the most plentiful mineral found in our bodies. Its found in our bones, teeth, nerve cells, body tissues and more. So where does our calcium come from? Mostly from cheese, milk and yoghurt although you also obtain it from leafy green vegetables, legumes and fruit.
But its not only useful to build our bones, but to build our cheese too. To make cheese we need to make sure the milk has enough calcium and in the correct form. It must be in a soluble form. Heating milk for pasteurization purposes changes the calcium from a soluble form to a colloidal (insoluble form). Other factors that influence the amount of usable calcium in the milk is storing milk, cooling milk and disturbing the milk due to transportation over long distances.
But lets start at the beginning:
Milk is made up of the following constituents:
To make cheese, the proteins in milk must stick together to form a lattice work or coagulum. Proteins are giant molecules built up of smaller units called peptides which in turn are built up of amino acids in a specific order. The milk protein casein is important in the manufacture of cheese. Other proteins, albumin, globulin and membrane proteins are largely left behind in the whey and are called whey proteins (used to make ricotta).
Casein constitutes about 78% of the milk protein. In milk it exists as calcium caseinate particles. These particles move freely in the milk. The rate at which they move depends on the temperature of the milk. They do bump into each other but are unable to “stick” to each other due to a protective shield on the outside of the particles. The particles are smaller than the fat globules which are also dispersed throughout the milk.
Under the influence of rennet, an enzyme from the stomach of a calf, or microbial rennet, the casein particles ( micelles) lose their protective shield which keeps them apart. The casein is now free to react with the calcium in the milk. The calcium forms bridges between the casein, linking the casein particles together to form a lattice work, (calcium caseinate forms calcium paracaseinate). Just imagine the scaffolding. This gives the milk its solidity, the milk has formed a coagulum.
The network of joined casein particles traps whey and all its constituents such as lactic acid, fat globules and bacteria inside it. When we cut the coagulum, we have curds, which are little bits of the lattice work with whey inside them.
If we have changed the form of the calcium in the milk by pasteurizing it or cooling and storing it, or we have utilised milk from cows that do not have enough calcium in their feed, we get a very sloppy curd that is difficult to cut. The calcium bonds are not very strong causing a weakened lattice work and the curd allows the whey trapped in it to leak out. You tend to get a milky whey. Goat milk in particular is very susceptible to low calcium. And it almost a given that when using a microbial rennet, one must add calcium chloride to the milk to get a firm coagulum.
To solve the above problems one can add calcium chloride to the milk. It is added at the beginning just before adding the rennet. It does need to be added in the correct dosage. Its a very cheap additive. Finest Kind sells the correctly weighed out calcium chloride crystals to which you just have to add water ( it costs money to transport the water!) Instructions are in the packet.
There is more to calcium when brining cheese – but that’s for another time.
Happy cheese making