Science of the Cheese making process

Doing groceries in the evening has one great advantage: a lot of fresh products have been discounted to help them being sold out by the time the store closes. We like buying these discounted products, they still taste perfectly fine, but it makes you try something else.

The other day there was even a whole display of discounted products in the supermarket, not because the day was nearly over, but because these were the last ones available. These displays barely ever have anything interesting, but this time there was a cheese making set!

So, there I was, making my own cheese (again) and I decided that it was time for some cheese making science basics! Great both for the homemade cheese scientist as well as larger scale producers.

Fresh cheese making process

The cheese making process, like any food production process, can be split into various separate steps. Here we will limit ourselves to the process for making a fresh cheese from already pasteurized (not sterilized) milk. That is, no bacteria or molds are added and no ripening processes take place. That leaves us with a process that can be done in one day:

  1. Curdle the milk
  2. Separate the watery phase (=whey) from the curds
  3. Press the curds down to create a firm cheese
  4. Eat, store, cook the cheese

Introducing: the milk

Cheese is made from milk, in most cases cow’s milk is used, which I will refer to here. Milk is made up of mostly water along with fats (depends on the fat content of the milk used), milk proteins (caseins & whey), lactose and a few minerals.

All about milk in one page
A quick re-cap on cheese.

Cheese on the other hand, barely contains any water. Therefore, one of the main steps of the cheese making process is to remove water from the milk. This is also the reason why you need so much milk to make cheese. One kg of cheese requires approximately 10 liter of milk.

So what ingredients stay in the cheese? These are the fats (which is why a skimmed milk will give only very little cheese and one that is less flavourful also), casein proteins and lactose. The water and whey proteins will not be used.

Step 1: Curdling the milk

So how do you manage to remove the whey proteins and water? This was discovered centuries ago. It is done by curdling the milk. When curdling the milk the cheese ingredients will sit together and form lumps in the milk. As a result you’re left with curds floating around in a liquid.

The watery phase which is left over is called whey. This can be poured off, leaving you with curds only. But we’ve gone pretty fast here. Why and how does milk curdle?

milk curdling due to acid addition

Caseins and curdling of milk

Milk is curdled by destabilizing some of the proteins in the milk. This destabilization causes them to clump together, forming curds. In the process, they take along other molecules such as fats in their curds.

The proteins causing this behaviour of milk are the casein proteins (as mentioned above, the whey proteins aren’t even incorporated in milk). In milk casein proteins form so-called micelles. This is a structure in which molecules arrange themselves in little ball like structures. Reason they do this is that casein molecules contain a part which likes to sit in water (hydrophilic) and a part which prefers sitting in fat (hydrophobic). The hydrophobic parts will all sit in the center of the micelle, whereas the hydrophilic parts sit on the outside. These micelles can be pretty large, up to 0,1 micrometer.

Casein proteins chemical reactions

These micelles are limited in their size thanks to one of the casein molecules, the κ-casein. The casein micelles will grow larger when this protein is neutralized, and thus cannot prevent their growth anymore. This is what happens when curdling milk.

Start curdling using acids or an enzyme

This κ-casein neutralization can be done in two ways:

  1. Add an acid (for example lemon juice or vinegar)
  2. Add chymosin (an enzyme which sits in rennet)

Commonly the acid and/or chymosin (it depends on the cheese type which is used and when!) is added to slightly heated or even boiling milk. Again, that all depends on the type of cheese being made.

curdling-milk-with-rennet
Curdled milk (this one was curdled using rennet, thus the enzyme and a little bit of acid).

Step 2: Draining the curd

Once you’ve been able to curdle the milk and thus gotten your cheese curds it is time to remove the whey. Before draining the curd though several additional steps can be taken. Sometimes the curds are heated, which should make them firmer (I assume because of the protein denaturation occuring) and sometimes additional ingredients such as salt are already added.

However, in all cases the whey will be split from the curds, generally using a cheese cloth. This is a fine mesh cloth which lets the whey pass through but keeps the curds in.

Step 3: Press the cheese

In some cases this step can be skipped, for example when making ricotta or another soft and moist cheese. However, in most cases the next step is to press the cheese. This process does nothing more than press out the remaining water from the cheese and tightening the curd texture. Pressing will make the cheese a more solid sturdy product.

Pressing the cheese can take more than a day, but it’s generally not the longest process.

When firm cheeses are made or mouldy cheeses, the next step is often ripening. During this process the cheese develops flavour and generally loses some more water.

A simple press for home use: something heavy (in my case a mortar) and two cutting boards.

Step 4: Enjoy

There are a lot of different cheeses with a lot of slightly different production processes. They also all taste and look completely different. A Dutch Gouda cheese is very different from a French brie which again is very different from an Italian Gorgonzola. They are consumed in different ways as well. Gouda is something I’d prefer with a slice of bread for lunch, whereas Gorgonzola is great in a pasta dish and where I prefer eating brie as an appetizer.

Make cheese

Now that you’ve learned the basic cheese making process it is time to make cheese. Continue reading to learn how to make Indian paneer and queso fresco or a soft cream cheese. In the second of those posts I’ll be using my discounted cheese making set!

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