How is Casein Manufactured? A Comprehensive Guide to Production

Casein is a family of phosphoproteins that makes up approximately 80% of the proteins in cow's milk, a fact central to its widespread use in the food and manufacturing industries. Its extraction and processing from skim milk involves several distinct methodologies that determine the final product's functional properties.

Quick Summary

Casein is produced from skim milk using three primary industrial methods: acid precipitation, enzymatic coagulation with rennet, or advanced microfiltration. Each process manipulates the protein's properties differently to yield distinct products like acid casein, rennet casein, or native micellar casein, which are then washed, dried, and milled.

Key Points

• Acid Precipitation: Casein is manufactured by lowering skim milk's pH to its isoelectric point (~4.6) with mineral or lactic acid, causing it to precipitate as a curd.

• Enzymatic Coagulation: The addition of rennet enzyme destabilizes casein micelles in milk, causing them to form a firm gel, a key step for producing rennet casein.

• Microfiltration: Modern production of native micellar casein uses membranes to physically separate large casein micelles from smaller whey proteins, avoiding chemical alteration.

• Ash and Calcium Content: Acid casein has low ash and calcium due to the acidic process, while rennet casein retains higher levels of minerals, and microfiltered casein retains its native mineral profile.

• Final Processing: After coagulation, casein curd is extensively washed, dewatered, dried, and ground into powder, with the final properties depending on the initial manufacturing method.

• Caseinates vs. Micellar Casein: Soluble caseinates are produced by adding alkali to insoluble acid casein, while micellar casein retains its natural, slow-digesting micellar structure.

The Fundamental Principles of Casein Production

Casein exists in milk as large, spherical colloidal particles known as micelles, which are stabilized by negative surface charges and interactions with calcium phosphate. The core principle of casein manufacturing involves destabilizing these micelles to cause the protein to coagulate and separate from the liquid portion of the milk, known as whey. There are two main traditional approaches to achieving this coagulation: altering the milk's pH to the casein's isoelectric point or using specific enzymes.

Raw Material and Preparation

Before coagulation begins, high-quality skim milk is required. The fat is removed from the milk using a centrifuge, as excess fat can negatively impact the quality and shelf life of the final casein product. The skim milk is also typically pasteurized to ensure food safety and eliminate undesirable microorganisms that could interfere with the process, especially in lactic acid-based methods.

Method 1: Acid Casein Manufacturing

Acid precipitation is a well-established method that exploits casein's insolubility at its isoelectric point, which is around pH 4.6. By lowering the milk's pH, the negative charges on the casein micelles are neutralized, causing them to clump together and precipitate out of the solution.

Mineral Acid Precipitation

This process uses inorganic acids to achieve rapid coagulation.

• Acidification: Dilute hydrochloric or sulfuric acid is added to pasteurized skim milk, which has been cooled to around 25–32°C.
• Coagulation: The pH is rapidly lowered to between 4.3 and 4.6. This causes the casein micelles to lose their charge and coagulate, forming a curd.
• Cooking: The mixture is then heated to 40–45°C for a short period to complete the coagulation process.

Lactic Acid Precipitation

This biological method uses bacterial fermentation to produce the acid.

• Inoculation: A mesophilic, non-gas-forming bacterial starter culture, such as Streptococcus lactisi, is added to the skim milk at a controlled temperature of 22–27°C.
• Fermentation: The bacteria ferment the lactose (milk sugar), producing lactic acid over a period of 14–16 hours. This gradual acidification causes a gentle coagulation of the casein.
• Heating: Once the target pH is reached, the curd is heated to firm it up before separation.

Method 2: Rennet Casein Manufacturing

Rennet coagulation is a different approach that relies on enzymatic activity, similar to the process used for making hard cheeses.

• Enzyme Addition: The skim milk, often with added calcium chloride to assist coagulation, is heated to around 30°C. Rennet, a preparation containing the enzyme chymosin, is then added.
• Micelle Destabilization: The enzyme specifically cleaves a peptide bond in the kappa-casein, a protein that stabilizes the casein micelles. This destabilization causes the micelles to aggregate and form a firm gel-like curd over 20–40 minutes.
• Cooking and Separation: The curd is cut and heated to inactivate the enzyme and expel more whey.

Method 3: Micellar Casein Production via Microfiltration

For manufacturers seeking a more native, undenatured form of casein, membrane filtration offers a solution that avoids pH shifts and enzymatic action.

• Microfiltration (MF): Pasteurized skim milk is passed through a system of semi-permeable membranes under pressure.
• Separation: The larger casein micelles are retained by the membrane, forming the retentate. Smaller components, including whey proteins, lactose, and minerals, pass through as permeate.
• Concentration: The retentate can be passed through the microfiltration system multiple times to increase the concentration of native micellar casein. This method produces micellar casein concentrate (MCC), which retains the natural structure and slow-digesting properties of the original milk protein.

From Curd to Powder: The Final Processing Steps

Regardless of the initial coagulation method, the subsequent processing steps are crucial for creating the final dry casein powder.

• Whey Separation: The initial curd-whey mixture is processed, often using a decanter centrifuge, to efficiently separate the solid casein curd from the liquid whey.
• Washing: The casein curd is washed multiple times with water. A counter-current washing process is often used to efficiently remove residual lactose, minerals, and whey proteins. This is a critical step for producing a high-purity product.
• Dewatering: The washed curd is further dewatered by pressing or centrifugation to reduce its moisture content, preparing it for drying.
• Drying: Hot air is used to dry the dewatered curd. Common methods include spray drying, especially for soluble caseinates, or using a two-stage process with a fluidized bed dryer for granules.
• Grinding and Packaging: The dried casein is then ground to a specific particle size and packed in moisture-resistant packaging to preserve its quality and shelf life.

Comparison of Casein Production Methods

Feature	Acid Casein	Rennet Casein	Micellar Casein (MF)
Coagulant	Mineral or Lactic Acid	Rennet Enzyme (Chymosin)	Membrane Filtration
Mechanism	pH shift to isoelectric point (pH 4.6) causes precipitation.	Enzyme cleaves κ-casein, destabilizing micelles.	Physical separation based on particle size.
Resulting Curd	Softer, less firm curd.	Firm, gel-like curd.	Retentate maintains natural micellar structure.
Ash Content	Low (around 2%), as minerals are lost during acidification.	High (around 8%), as calcium phosphate is retained.	Variable, can be controlled by process parameters.
Calcium Content	Low	High	High (preserved from natural milk)
Solubility	Insoluble in water. Can be converted to soluble caseinates with alkali.	Insoluble in water, good for cheese applications.	Retains native solubility characteristics.
Typical Uses	Caseinates (emulsifiers, stabilizers), plastics, adhesives.	Processed cheese, specialty foods.	Sports nutrition, nutritional supplements, high-protein yogurts.

Conclusion: A Diverse Manufacturing Landscape

The manufacturing of casein is a versatile process with significant implications for the final product's properties and applications. The choice between acid, rennet, or microfiltration methods depends on the desired outcome, whether it's a water-soluble caseinate for a coffee whitener, a firm curd for cheese production, or a native, slow-digesting protein for a sports supplement. By controlling the coagulation and processing steps, manufacturers can produce a range of casein products that are vital to the food, pharmaceutical, and industrial sectors. For more on casein's properties and uses, check out the Encyclopaedia Britannica article on the subject.

References

• Britannica: https://www.britannica.com/science/casein
• Wikipedia: https://en.wikipedia.org/wiki/Casein

Frequently Asked Questions

What is the primary raw material for manufacturing casein?

The primary raw material used for manufacturing casein is high-quality skim milk, which is milk with the fat removed via centrifugation.

What is the difference between acid casein and rennet casein?

The main difference is the coagulation method. Acid casein is precipitated by adding acid to skim milk, while rennet casein is coagulated using an enzyme called rennet.

How does microfiltration produce casein?

Microfiltration uses semi-permeable membranes to physically separate the larger casein micelles from the smaller whey proteins and other milk components, resulting in native micellar casein.

Why is casein washed after coagulation?

Washing the casein curd multiple times is crucial to remove residual lactose, salts, and whey proteins, which ensures a high-purity product with better quality and keeping properties.

What are caseinates?

Caseinates are water-soluble forms of casein, such as sodium or calcium caseinate. They are produced by dissolving insoluble acid casein curd in an alkaline solution.

Why does rennet casein have a higher ash content than acid casein?

Rennet casein retains the colloidal calcium phosphate that is naturally associated with the casein micelles in milk. In contrast, the acidification process dissolves and leaches these minerals from the curd, resulting in a lower ash content for acid casein.

What is the main advantage of micellar casein?

The primary advantage of micellar casein produced by microfiltration is that it retains its native micellar structure. This allows it to form a gel in the stomach, providing a slow and sustained release of amino acids for several hours.