curdled milk

How Cheese is Made – A Complete Process Overview

There is not one way to make cheese. Instead, there are hundreds, if not thousands of ways to make cheese. Resulting in countless different types of cheese with each their own characteristics. Even within one variety, there are countless little tweaks that you can make that will impact the color, flavor, texture, and more of the final cheese.

As such, don’t expect and detailed a step-by-step guide. Instead, we’ll walk you through the most commonly used process steps. From curdling to pressing to ripening. We’ll introduce you to the complex, but fascinating world of cheese making.

It all starts with milk

Cheese starts out as milk. Most of that milk is made up of water with about 5% each of sugar (lactose), proteins (casein and whey), and fat. The exact composition depends on the animal the milk is from, as well as the time of year, the feed the animal has eaten, and more.

Cheese increases milk’s shelf life

Milk is a highly nutritious product, however, before the days of refrigeration, it could only be kept for a short amount of time. So people had to find ways to make milk last longer to have enough dairy throughout the year.

Making milk into cheese is one way to preserve milk for a longer period of time. Some cheeses remain of good quality for years. Some even only reach their peak quality after more than a year!

Cheese can be kept for longer than milk since it’s a concentrated version of milk. The cheese contains most of the fat and proteins originally present in the milk, without the excess moisture that makes it prone to spilling.

You need a lot of milk to make cheese. 1 liter of milk may only give you 100g of cheese. The exact yield will depend on the type of cheese as well as the type of milk it is made from.

Cheese is curdled milk

To make cheese from milk, the milk is curdled. In curdled milk, the casein proteins have become unstable. They cluster together to form large curds. These curds also trap fats and other components from the milk such as calcium.

To make cheese, these curds are removed from the remaining liquid, called whey. The whey still contains about 20% of the overall proteins, called whey proteins. Some cheeses (such as ricotta) are even made from whey, although the vast majority of cheeses are made from the curds.

What about plant-based milk?

You can make cheese without animal milk. Instead, they might be made with other plant based sources such as nuts, cashews, in particular, are popular. However, for the scope of this article, we’ll only focus on milk made from animal milk, whether that’s from a cow, goat, or buffalo. The reason for doing so is that making cheese from animal milk has some fundamentally different process steps and underlying science. For instance, plant milks don’t contain casein.

freshly pressed paneer
One of the easiest cheeses to make at home: paneer.

The cheese-making process

As quickly alluded to in the introduction, there is not one way to make cheese. There are many. Some cheeses follow all of the steps mentioned below, whereas others only require a few. Keep in mind also that even when following the exact same steps, the results may be different because of slight nuances in how the steps were executed or differences in the quality of the milk.

Step 0: Standardization & pasteurization

Before the actual cheese making starts the milk may be pre-processed to get it ready.

Standardizing fat content for reproducibility

In larger production facilities most milk is standardized. Standardized milk is milk with a constant fat content. Milk from a cow varies in fat content by season and diet. By having a constant amount of fat in the milk, factories know exactly how the milk will behave during the process. It will ensure that the resulting cheese always has the same amount of fat.

To standardize milk, all the fat is removed from the milk, before it is put back in in the desired quantity. During this step, manufacturers may also decide to make milk with a lower fat content than that of fresh milk. This allows manufacturers to make cheeses with a lower fat content than would usually be expected.

Raw vs pasteurized milk

Freshly milked milk is raw, meaning it has not undergone a heat treatment. Some cheese manufacturers solely use this raw milk to make cheese since heat can impact the structure and functionality of some of the milk proteins, impacting the quality of the cheese. However, it does mean that potential pathogenic bacteria might still live in the cheese.

To kill off these microorganisms that make us sick milk is often pasteurized. Pasteurization is a less intense heating process than boiling milk, but it’s intense to kill the most harmful microorganisms. Pasteurized milk is also used for many types of cheese.

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Which of the two is used depends on a variety of factors such as local legislation, the type of cheese, and the facilities in which the cheese is made.

Step 1: Acidification & coagulation

Once the milk is ready for use, it is time to curdle the milk. For curds to form in milk, casein proteins need to be destabilized. This can be done in two ways:

  1. Through acid: acid can either be added directly, but more commonly acid is made by converting the lactose in milk into lactic acid, often using microorganisms to do so.
  2. With enzymes (rennet): enzymes cut into the casein proteins, causing them to form curds.

Cheeses can be made with one or a combination of the two methods. A disadvantage of solely using added acids is that the pH value of the final cheese will be quite low. This may inhibit a lot of the flavor formation processes catalyzed by enzymes during later steps of the process as well as the overall texture of the cheese. It’s why the vast majority of cheeses is made with rennet and/or microorganisms that convert lactose into acid.

Starter bacteria acidify the milk

To convert lactose into lactic acid, the help of a specific group of bacteria is required: lactic acid bacteria. Lactic acid bacteria specialize in converting lactose into lactic acid. Keep in mind that bacteria are living microorganisms. They thrive under certain conditions but will die or stop growing when handled incorrectly.

The bacteria added during this step are generally referred to as starter bacteria or primary cultures. Later on in the process other microorganisms may be added as well.

Enzymes cut proteins

Traditionally, rennet was found in the stomach lining of calves. People discovered that it was great for curdling milk. Nowadays, we know that it does so because of the presence of various specialized enzymes, such as chymosin.

Enzymes are a specialized type of protein. They are very good at doing one specific job: catalyzing specific chemical reactions. Each enzyme has its own specialty, but also its own conditions under which it thrives.

Rennet is still ‘harvested’ from a calves stomach, but can also be made by using specialized microorganisms. They have been grown to produce these specific ingredients. There even is a plant that contains ingredients that work very similarly to those of calves’ rennet. However, it’s a little less commonly used.

Mostly done at moderate temperatures

Most lactic acid bacteria do not like high temperatures. It’s why pasteurization is such an effective method to kill off a lot of microorganisms. It is also why this first step is generally done at quite mild temperatures, around 30°C (86°F). Lactic acid bacteria thrive under these conditions and so do the enzymes in rennet.

Some cheeses are ‘done’ after step 1

For some cheeses, this is where the journey ends. Think of cottage cheese or cream cheese.

curdled milk
Curdled buffalo milk, using acid

Step 2: Cutting and draining the curd

An easily overlooked, but important, step comes up next: cutting the curds. Using knives the curds are sliced into pieces to make further processing easier. The size into which they are cut has a big impact on the cheese’s final texture. Smaller pieces of curd lose their moisture more easily. As a result, this makes a harder, firmer cheese. Large pieces of curd on the other hand do not loose as much moisture and make moister and softer cheeses.

Heat may help with water expulsion

During this step, the curds may be warmed up slightly. This additional heat helps expel more water from the curds, again impacting texture. The heat may also speed up various desirable chemical reactions and the growth of microorganisms which positively impact the flavor of the cheese.

Adding salt for taste & shelf life

To most cheeses salt is added at some point during this step. The salt doesn’t just lift up the flavor, it also impacts texture and has a crucial role in extending the shelf life of cheese. Salt can prevent the growth of harmful microorganisms.

For some cheeses, salt is mixed in with the curds. For others, the salt is smeared on the outside. Yet another method is to immerse the cheese in a salty brine for some time. During this time they absorb quite a bit of salt. Feta and halloumi have both been brined.

Hard cheeses are pressed to expel more moisture

Once the curds have been cut, they are removed from the remaining whey. For some cheeses, simply draining off the whey is sufficient. However, especially for harder cheeses, it is important to remove quite a bit of moisture. It’s why, after the curds have been drained off, they’ll be pressed for quite some time. The exact duration depends on the type of cheese.

Not all curds are cut and pressed

Not all curds are cut or pressed during this step. Some are merely drained from the excess whey before being processed further in the next step. This makes softer cheeses.

Other curds are lightly cut and drained and then stretched and kneaded. This makes fresh mozzarella cheese for instance.

A simple press for home use using a mortar, cheese cloth and cutting boards.

Step 3: Ripening

Some cheeses are ready to eat immediately after step 2, others, still need over a year before they’re ready. During this ripening process, the flavor of cheeses changes considerably. Enzymes continue to do their thing, (some) more moisture may evaporate and other chemical reactions continue to occur.

Adding secondary cultures

To further the flavor development of cheese, a next set of microorganisms may be added to the cheese. This generally happens either at the end of step 2 or during step 3. Both a new set of bacteria, or specialized molds may be added to the cheese. Roquefort, camembert, Silton, they’ve all had additional microorganisms added to them to develop more flavor. The molds are responsible for the blue color in these cheeses.

Controlling temperature and humidity

For the flavors of cheese to properly develop during this step, it is crucial that the cheese is stored under the right conditions. Generally speaking, that’s at a temperature in between that of the fridge and room temperature. Also, ideally, it’s quite a humid environment, though not too excessively.

It’s why you might see special cheese caves for certain types of cheeses. Caves are known to have a constant temperature and humidity so have always been great for ripening cheeses over time. The conditions within the cave greatly impact what types of cheese are best made in it.

Step 4: Packaging

Last but least, cheeses need to be wrapped before being shipped out. The type of packaging very strongly depends on the cheese. For instance, a large, round, wax-coated, uncut gouda cheese already has a protective layer. It only needs additional packaging once it’s been cut into pieces.

Paneer on the other hand spoils quickly and is quite firm. Vacuum packaging is a great solution here. A soft brie however needs to be handled more gently or it will be squashed completely. Grated cheese is yet another story. Because of its large surface area, it is very vulnerable, so needs to be packaged in a protective atmosphere.

An outlier: the simplest (?) way to make cheese

The vast majority of cheese follow (some) of the steps above. But, of course, there are a few outliers. One of those are a class of fresh cheeses that strictly don’t follow any of the steps above.

These cheeses are made by boiling milk and directly adding an acid such as vinegar. The acid causes the milk to curdle almost instantaneously. Next, the curd is strained to remove the whey. A final compression helps the curds to stick together and the cheese is pretty much ready to use.

Examples of cheese made this way are paneer and queso fresco. These are firm cheeses that don’t melt when heated, because of the way in which they’ve been made.

Since the milk for these cheeses needs to be brought to a boil, there is no need to pasteurize them. The boiling step also kills pathogenic microorganisms.

References

Harold Mc Gee, On Food and Cooking, p. 51-67, 2004, review

Meneer Wateetons, Over rot 2.0, 2nd edition, 2020, p. 240-254

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2 Comments

  1. Thanks and congrats for this very good and amazingly illustrated article on cheese making. I am a big fan of your blog which is a source of inspiration for mine.

    • Bonjour!

      Thank you for your great comment, I’m happy to hear you like the blog and its content. Hope it helps you. Happy to hear whether you’d have topics you’d like to read more about.

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