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How Casein Proteins Are Crucial For Making Cheese

Even though you can make a lot of different types of cheese from cow’s milk, at their core, they all work the same way. Whether it’s brie, a fresh herby cheese, mozzarella, Gruyere, Parmesan, Gouda, paneer, or Emmentaler, they all rely on a crucial component: casein proteins.

Casein proteins are special. In milk, they just float around, invisible to the eye. But, the addition of acid or rennet, under the right conditions, causes them to clump together, forming curds. The key to making cheese.

What are casein proteins?

Casein proteins are a group of proteins that are naturally present in animal milk, including cow, human, goat, and buffalo milk. Despite the name, casein proteins aren’t just one type of protein. Instead, casein proteins consist of four different types:

  • αs1
  • αs2
  • β
  • κ

They’re all proteins, meaning they are all made up of a chain of amino acids. However, they all have a slightly different structure and thus behavior. None of them seem to have a very well-defined 3D structure though, which is quite unusual for proteins.

Casein proteins make up about 70-80% of the protein content of milk. The remainder is made up of whey proteins.

Caseins form micelles

Casein proteins don’t like to sit in water. Instead, they prefer to cluster together. As such, in milk, casein proteins don’t float around individually. Instead, they cluster together in so-called micelles. Each micelle is made up of all 4 types of caseins, though not in equal amounts. Over 90% of a micelle is made up of these proteins, the rest is made up of calcium phosphate. It’s where the calcium present in milk ‘hangs out’.

These micelles are complex in structure and scientists still don’t fully agree on their structure. What is known is that κ-casein can be found mostly on the outer layer of the micelle, whereas the others make up the center of the micelle. As a matter of fact, it’s the κ-casein that prevents all casein proteins from clustering together. Instead, it ensures the formation of the smaller micelles.

Casein proteins chemical reactions
Simplified graphical representation of casein protein behavior.

Casein makes milk turn white

Interestingly, without these casein micelles, milk wouldn’t be white, it would be translucent. The micelles are small (50-500 nm), however, they’re large compared to the size of molecules. Their size allows them to reflect light. This scattering reflection causes us to perceive milk as being white. It’s also why, when making cheese, the remaining liquid is no longer white, it’s translucent. All the casein micelles have left this liquid to sit in the cheese.

diced fresh paneer
Paneer, a fresh type of cheese

To make cheese, casein curdles

In milk, casein proteins just hang out as micelles. However, humans have found out a long time ago that we can destabilize these micelles. Of course, at the time, people didn’t know they were casein micelles, but, they did know that the milk could be curdled and made into cheese. This curdling is the destabilization of casein micelles.

Making cheese 101

To make cheese from animal milk, you add either rennet or acid (this is how to make paneer for instance) to warm milk. The addition of either ingredient causes the milk to curdle. During this process thick ‘curds’ form within the milk. These curds are then removed from the remaining liquid (the whey) and pressed into cheese.

The whey that’s left over after making cheese contain a lot of whey proteins, the other major protein in milk. Whey proteins do not curdle during cheese making.

Curdling milk

Casein micelles destabilize due to acid

Casein proteins and the micelles they form, can handle heat very well, unlike egg proteins for instance. It’s why you can cook milk, without it greatly affecting the appearance and taste.

Even though they can handle heat, they can’t withstand acid. Once the pH value of milk drops to a value of 4.6, the micellar structure becomes unstable. The structures are no longer stable due to a change in charge of the overall system. Instead, the casein proteins will form larger, more complex structures, referred to as curd. These no longer just contain calcium, they also ‘capture’ most of the fat that’s present in the milk.

Or enzymes cut κ-casein

Recall how κ-casein can be found on the exterior of the casein micelles? Here it serves an important function to stabilize the micelle as a whole. If you’re making cheese using rennet, you’re attacking these κ-casein proteins. The enzymes in the rennet, of which chymosin is one, break down κ-casein, but don’t affect the other types. The enzyme cuts the protein into two pieces, always at the exact same spot, resulting in two smaller proteins. These proteins can no longer stabilize the micelles.

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Again, this causes the casein proteins to curdle and form large curds structures, suitable for making into cheese.

Extra calcium helps the cheese

Calcium salts are part of the casein micelles, but they’re also a crucial part of cheese curds. To help form more of these stable cheese curds, cheese makers may actually add additional calcium in the form of CaCl2.

Curd’s texture depends on the conditions

Using acid vs. rennet has a profound impact on how the casein proteins cluster and form curds. If you’d zoom in, you’d notice they’d be organized differently. But, other aspects can play a role as well. The above mentioned impact of calcium concentration is one, but so is the impact of salt and the composition of the milk itself. All contribute to nuanced differences between cheeses that are otherwise made the same way.

Dutch cheese gouda
A typical piece of Dutch cheese, made with rennet.

Casein during a cheese’s shelf life

Once cheese has been made, the main role of casein is over. It’s done its job. However, it will continue the behavior of the final cheese. For instance, many cheeses are ripened. Whether it is and for how long depends on the style of cheese. During this time changes in the casein may again occur. Some types of casein proteins may be broken down over time and some reorganization of the proteins may occur. This continues to impact the consistency and even flavor of the cheese over time.

Stringiness is caused by casein

Some cheeses become stringy when they’re melted. Since casein proteins play such a crucial role in forming a cheese’s structure it probably won’t surprise you they’re involved here as well. The stringiness is caused by casein proteins linking together into long fibers. If the casein is broken down during ripening, the casein proteins become too small to form these strings. As such, they will be less stringy when melted.

Sources

Scientists have been stumped by the structure of casein micelles and so there is a lot of scientific literature on the topic. Unfortunately, less has been written about what happens to casein proteins during the cheese-making process!

Farrell, Jr, Harold & Malin, E.L. & Brown, Eleanor & Qi, Phoebe. (2006). Casein micelle structure: What can be learned from milk synthesis and structural biology?. Current Opinion in Colloid & Interface Science. 11. 135-147. 10.1016/j.cocis.2005.11.005. link

C.G. de Kruif, Advanced Dairy Chemistry – 1: Dairy proteins, Jan-2003, link

De Kruif, C.G. (Kees) & Huppertz, Thom & Urban, Volker & Petukhov, Andrei. (2012). Casein micelles and their internal structure. Advances in colloid and interface science. 171-172. 36-52. 10.1016/j.cis.2012.01.002. link

Harold McGee, On Food and Cooking, p. 64-65, see review

R. Scott, Cheesemaking practice, third edition, p.50

Patrick F. Fox, Paul L.H. McSweeney, Timothy M. Cogan, Timothy P. Guinee, Cheese: Chemistry, Physics and Microbiology, Volume 2: Major Cheese Groups, Elsevier, 2004, link

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11 Comments

  1. My son has a dairy protein intolerance and we are slowly trying to reintroduce it to see his reaction. I was told Mozzarella is a less strong cheese when it comes to the protein. Is this correct and if so cheeses are the least amount of dairy proteins and what cheeses are the strongest?

    • Hi Heidi,
      Thanks for your question! In general, all cheeses will contain a considerable amount of protein, however, in more moist cheeses that content is slightly lower per ounce or 100g of cheese since there is more moisture in there. I’m thinking that is one of the reasons people may have recommended Mozzarella. Mozarella and other fresh cheeses still contain a lot of moisture and may therefore contain slightly less protein per portion. Harder, drier cheeses will still contain the same protein but more moisture has evaporated, increasing the protein content. What you might also consider is a processed cheese type to start with, in various cases (e.g. cream cheese) the actual milk protein content isn’t as high because of the addition of other ingredients.
      That said, which type is best to start with when you have (had) an allergy I wouldn’t be able to say since I’m not a dietician nor an expert on food allergies. A dietician might be able to give you more specific advice.

    • Hi Jenny,

      Thanks for your questions but unfortunately I don’t have a good answer. All dairy made cheeses contain some amount of casein since it is what makes cheese a cheese. Without the casein, the milk wouldn’t set and form the cheese curds. The main variation in casein contents will likely be related to the amount of fat and moisture in cheeses. If there is a lot of fat and water in a cheese, almost automatically there is less protein (thus casein) in the cheese. That said, there still is casein in there.

      Hope that helps at least a bit!

  2. What cheese has the highest casein?

    I understand concept of driest but not being familiar with cheese variety can you give some names?

    When I search it seems to default to “least” for those with allergies but I’m trying to find highest casein to buy and try to make homemade.

    • Hi Lauren,

      If you’re making cheese from just milk and some enzymes or acids, the composition of your milk will determine the composition of your cheese (assuming you’re not adding any other protein sources etc.). The more water you remove from the milk, the higher the protein-% of the cheese (but the less overall weight of cheese) you’ll end up with. Also, a milk with a lower fat content will result in a cheese with a higher protein content (but less cheese in overall).
      To illustrate, let’s assume you have 1000g of milk that you’re making into cheese. We can assume that all the casein in the milk will end up in the cheese, let’s assume there’s 5%, that is 50g. If you make 500g of cheese out of this milk (not adding anything else except for enzymes), you’ll have 50g/500g*100=10% casein. However, if we dry the cheese for longer and press it more, you right end up with only 250g of cheese, now your casein content will be 50/250*100 = 20%. How much water gets expelled will impact casein content. So, if you’re making your own cheese, one that is drier (e.g a parmesan instead of a fresh mozzarella) will have a higher protein-%.

      A similar story goes up for fat. If you remove all the fat from your milk, and aim for a similar moisture-% at the end, you will also end up with more protein. An example, again you have 1000g of milk of which 5% is fat. In this case you’re removing all the fat, so you’ve only got 1000-(0.05*1000)=950g milk. Again, you’re removing 500g of moisture from the cheese (same as above where you made 500g of cheese from 1000g of milk, for simplicity we’re assuming you’re removing the exact same amount of water). The protein content will now be 50/(950-500)=11.1% protein. So your protein content is higher because there’s no fat left. (This calculation is a bit of a simplification of reality, but good enough for reality).

      When making cheese at home especially, all these factors are important since you might not be able to standardize as well as large scale manufacturers are. So knowing just how much fat your milk contains (this can differ per season) can be important.

      I know you’d like to know specific names of cheeses but since there are so many types of cheeses (hundreds, if not thousands) I want to make sure you understand the concepts so you can choose yourselves. Generally, going for a pretty dry cheese like a parmesan or a low-fat aged Gouda or cheddar. Personally, I would suggest you choose a type of cheese you’d like to make and within that realm find one that has the highest casein content.

      Good luck!

  3. Hello,

    Thank you for writing this! It was fascinating. I have a casein intolerance, and I was trying to understand why I can eat some cheeses without it irritating my body (such as cheddar), yet the whiter cheeses tend to make me react the same as if I were drinking milk.

    I knew it had something to do with enzymes/the casein breaking down in the cheese making process. It’s really interesting and surprising that we don’t fully understand how it all works!

    -Rebecca

  4. Anelle, hello! Testing for protein and fat content of fresh unpasteurized milk (at a farm point, that is): could FoodCrumbles provide concrete guidelines or suggest sources one can further research? What about powder milk with a protein content of 18-23% before dilution– what “kind of homemade cheese” would one get? Why powder milk? This IS the most popular type of milk available at my location. Good quality pasteurized and sterilized milk can be had at a premium cost. I’d think that fresh unpasteurized milk gives a top premium flavor to a homemade-well-ripened cheese.

    • Hi Rodrigo,

      I’m afraid that I’m not exactly sure what it is that you’re asking, but I’ll give a few pointers below. If that doesn’t answer your question, please let me know!

      Protein and fat content are generally measured in a laboratory, or using techniques such as spectroscopy. Best to connect with a local laboratory who have the expertise in your area, also with regards to possible legislative requirements. There is not 1 value that’s good or bad, it depends a lot on which type of cheese you’re making, the season, etc.

      A reason for using unpasteurized milk for making cheese is that it will result in a different flavor, since heat treatment has not broken down certain enzymes as well as microorganisms that can contribute to flavor. It does need to be processed in a very hygienic manner since the risk of it containing pathogenic micro organisms is a lot higher (it’s why for instance it is not recommended to eat cheese made from unpasteurized cheese when a woman is pregnant, as a precaution). It’s also why you shouldn’t store unpasteurized milk for a long period of time, it will give the microorganisms the chance to grow.
      Powdered milk has undergone quite a few additional process steps including heating and drying that will have influenced the milk and its proteins. I’m not aware of cheese being made from powdered milk, though that doesn’t mean it’s impossible per se, though it might well behave different than cheese.
      Another reason that it’s a little counterintuitive to use powdered milk to making cheese is that you’ve already removed all the water from the milk. Now, you’re adding it back, to then again remove a lot of it again. From an energy standpoint, it’s not very efficient. Both cheese and powdered milk are ways to conserve milk and keep it good for longer.

      Some articles on FoodCrumbles you might find helpful:
      Cheese making process
      Pasteurization

      Hope that helps you out!

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