The Large-Scale Manufacture of Casein From Milk

The large-scale manufacture of casein from milk involves several steps, from sourcing raw milk to processing it into various forms of casein for industrial use. It is one of the most important food proteins in the world and has been extremely well reviewed over a number of years (Scherer, 1906; Fox & Mulvihill, 1990; Ventimiglia & Birkenhager, 2012; Scherer, 2015).

The protein is a generic name for a family of similar phosphoproteins, They make up 80% of the protein in cows milk and between 60 and 65% of the protein in human milk. The remainder of the total protein in milk are the whey or serum proteins. As well as being the main component of all cheese it is also found in nutritional foods for athletes. It can also be found in a range of industrial products including safety matches.

The methods of producing and purifying this protein have been covered over many years because it is so important in food. There are two methods and both use skimmed milk which is defatted milk. Casein is produced either by acid precipitation or rennet coagulation. 

The production of purified casein has been an industrial process for well over a hundred years. The original method was devised by Hammarsten which is the acid precipitation method. That method separates casein from diluted milk by means of acid, filtering and washing the
separated casein and then dissolving it in dilute alkali. The processes of coagulation by acid, filtration, washing, and redissolving are repeated four or five times. This process has been modified over the years mainly to reduce the amount of calcium phosphate left over along with calcium caseinate which is soluble in salt solutions and also reduce the degree of general hydrolysis. The process was examined by exploiting the coagulation of milk which left all the salts in solution (Van Slyke & Bosworth, 1916). The method was refined further (van Slyke & Baker, 1918).

It’s worth looking at US Patent 2468730A from 1949 which was granted to the The Borden Company (New York). The general process is usually defined as a batch method but it has also been developed for continuous processing.

This post cover the process, detailing each step in the production of casein. We have separate articles on the production of whey and its fractionation.

The Market For Casein

The interest in casein is frankly staggering. The global market is now US$ 2.7 Billion according to Future Market Insights in 2023 and the CAGR to 2033 is 6.3% where it will reach a value after a decade of US$ 4.9 Billion. What is termed the global market absolute dollar growth (US$ million/billion) is quoted as US$ 2.2 Billion.

The main global producers are Lactalis Group, Fonterra Co-operative Group, Royal Fries Campina N.V., and Savencia Fromage. The main brands using casein as an adult sports nutrition product are Optimum Nutrition, MyProtein and BSN.

Sourcing Milk

The process begins with the procurement of fresh, high-quality milk. Dairy farms supply bulk quantities of milk to casein manufacturing facilities. Quality control measures are implemented to ensure that the milk meets regulatory standards and is free from contaminants. In Europe, there are many different cow varieties that supply milk although Friesans dominate because of their overall high milk yields. In the USA it is .

Milk Reception, Pasteurisation and Standardization

Upon arrival at the manufacturing facility, the milk undergoes reception and standardization. This involves testing the milk for quality parameters such as fat content, protein content, acidity, and bacterial load. Based on these tests, adjustments may be made to standardize the milk composition to meet specific requirements for casein production.

Milk does not have to be raw! It can be pasteurised or sterilized (72ºC for 15-20 seconds HTST process or 140ºC for 3 seconds in a UHT process). The HTST process is favoured in the USA whilst Europe favours UHT. The different degrees of pasteurization mean that in the USA milk tends to be sweeter because HTST is not as harsh as UHT so lactose is retained. In a number of cases skimmed milk might be the main source because it has already been partially processed to remove fat and it reduces the costs of purification for the processor. Another feedstock for further processing is impure casein itself. The composition of UHT skimmed milk is casein ca. 25 g/l, whey proteins ca. 6.4 g/L, lactose 46 g/L and calcium 1.2 g/L (Al-Akoum et al., 2002).

It is generally the case that as much of the whey proteins, fat, lactose sugar and minerals are removed to help maintain the stability of the casein.

Separation of Milk Components

Next, the milk is separated into its major components: fat, casein protein, and whey. This separation is typically achieved through centrifugation or filtration processes. The protein fraction, which contains casein, is isolated for further processing. Ideally, the milk is defatted before the steps of separating the casein from the whey.

Filtration in its early stages has been employed to separate casein from whey proteins using microfiltration. In such cases filtration is employed with the focus on purifying the whey proteins and discarding caseins.

Acid Precipitation or Enzyme Coagulation of Casein

The isolated protein fraction is subjected to coagulation or precipitation to separate the casein from the whey protein. This coagulation can be achieved through acidification or enzymatic action. Much of the chemistry of coagulation is directly related to the behaviour of the casein micelle.

• Acid Coagulation to Produce Acid Casein By Microbes, Mineral Acids and Cation-Exchange Resins

In this method, food-grade mineral acids such as hydrochloric acid, sulphurous acid, sulphuric acid, hypochlorous acid, and organic acids such as lactic acid, citric acid, formic acid and even chloracetic acid are added to the protein solution. Even ‘acidic’ gases (those of mineral acids) such as sulphur dioxide and trioxide, and hydrogen chloride have been used.  This lowers the pH causing the casein proteins to precipitate out of solution. The whey proteins remain soluble and can be separated from the casein curd.

The ideal pH for precipitation is between 4.5 and 4.6 which is the isoelectric point of casein. All acid coagulation methods work to this pH.

In the US patent milk is warmed up to 100ºF. The acid is added with stirring until the pH drops to the point where curds form. Curd granules formed by careful precipitation helps with further processing especially filtration. In some cases treatment of the milk with acidic gases can occur at room temperature and even below (45ºF). The level of precipitation is still viable as a business even at low temperatures.

In the mineral acidification process, milk is heated to a temperature of 32ºC. Acid is added to drop the pH to between 4.3 and 4.6. After the desired pH, the milk is heated to 40 and 45C using a plate heat exchanger and held for two minutes where smooth clumps of casein are formed. The whey is removed by washing using a decanter. The process of washing and drying is similar to that of the preparation of rennet casein at the casein curd stage.

In the biological acidification process, lactic acid is produced through microbiological action. The milk is pasteurised and cooled to between 23 and 27 ºC. A non-gas producing starter is added. The acidification takes 15 hours or more. It is not an easy process to control because of the nature of the fermentation. It requires large tanks and the degree of acidity can vary markedly. When the correct acidity is reached, the milk is stirred then heated to between 50 and 55ºC using a plate heat exchanger.

There is another variant which is not commonly found based on the application of cation exchange resins which has been tried in dropping the pH.

• Enzymatic Coagulation to Produce Rennet Casein 

Alternatively, enzymes such as rennet (chymosin) or microbial proteases can be used to coagulate the casein. The alternative name is renneting. These enzymes specifically cleave the bonds between kappa- casein molecules, leading to the formation of para-kappa casein which is a casein curd along with casein macropeptides. The second part is then coagulation of that para-kappa casein. Rennet casein has a protein content of 91% and is often used in various formulas as well as baits and animal feeds.

In this process, the milk is heated for a brief time  and then cooled back to 30ºC. The milk is held in a stirred vat. Rennet is added whereupon a gel forms after 15 to 20 minutes. The coagulum is cut and stirred whilst being heated to 60ºC. This temperature deactivates the enzyme and the whole process takes up to 30 minutes.

When the two methods are compared.

Other Methods of Producing Casein

A couple of other forms of casein exist. One is a co-precipitate which is produced by heating skimmed milk to a high temperature and then precipitating the whey and casein protein complex with calcium chloride. The other form is sodium caseinate which is acid casein dissolved in sodium hydroxide.

Other alternative methods of cogulation/precipitation include ethanol precipitation, electrodialysis with mineral acid addition,  direct ultrafiltration followed by cryo-destabilization, high-pressure carbon dioxide precipitation, addition of anionic polysaccharides .

Casein Curd Formation

Once coagulated, the casein forms a gel-like curd sometimes called a casein curd, which can be further processed to remove entrapped excess whey, lactose and water. The curd is typically cut into smaller pieces to facilitate drainage and whey removal. Curd is decanted using a centrifuge (separator) or even a simple sieve from most of the whey protein, denatured rennet, salt and lactose in solution. The liquid whey is sent on for further processing.

The components entrained in the casein curd affect the washing stage.

Washing

Washing can be either a batch or a continuous process. Originally, rennet casein was produced in special vats as a batch process but the continuous method is preferred.

If the curd is too fine, economically unacceptable amounts of casein are lost in the wash water. If the curd is too tough, it is more difficult for any impurities to diffuse out with the wash water.

Batch Washing

The casein curd is washed at between 45 and 60 ºC in a tank to remove residual whey and lactose, which helps improve the purity of the final product. It is further decanted to remove extraneous liquid. Washing may be repeated several times (at least twice) to ensure thorough removal of whey proteins and other impurities.  In some cases the casein curd is redissolved and then precipitation is repeated. 

Continuous Washing

In the continuous system, whey is drained off the casein curd before the latter passes through between two or three wash tanks with agitators. A decanter is the best separator in this case to remove whey because water consumption is lowest. Dewatering between each wash stage uses specialised sieves called inclined static strainers or with decanters. After each wash stage, the casein curd with water will pass through another decanter to get rid of as much water as possible before final drying.

In very large operations, casein coagulation occurs in batch systems using a certain number of vats which are emptied as when they are required to keep feeding the dewheying and washing plants. In these systems, washing uses a countercurrent process rather than cocurrent because it is more economical.  

In the countercurrent system pure water washes curd that has been washed earlier. The wash water which contains impurities from previous washing will partially clean fresh curd. It is still the most efficient and effective method of using water in such a process. The countercurrent system uses between 0.3 to 0.4 litres of water per litre of milk compared to 1 litre in a cocurrent system.

The degree of washing defines the purity of the casein. Two stages is a minimum requirement. The last stage only uses fresh water.

Dewatering & Drying

Following washing, residual moisture needs to be removed to reduce the load on the driers. The washing temperature is important in curd drying because it affects texture. This next step is the dewatering stage. When high wash water temperatures are used as in the previous step, more water is released during dewatering but it creates a tougher and more plastic curd that is harder to dry. The washing temperature must be controlled to optimise moisture requirement and the friability of the curd (Southward, 2002; Hills, 2011).

The casein is always decanted where it achieves a dry matter content of 40 to 45%. 

In some cases a dry soluble product is best obtained by raising the pH of the casein to between 6 and 7 by adding ammonium hydroxide. Alternatives can be sodium carbonate, sodium hydroxide and even quaternary compounds of amines as long they are food grade and their addition is manageable.

After washing using the batch washing system, the casein curd is filtered and then hot air-dried to reduce its moisture content and form a powder or solid mass. The moisture content of the casein curd at this point will be 12%. If it is continuous washing employed, the casein having been dewatered to that DM of 40% or more is further dried in a vibration dryer. 

Drying uses any number of methods from ovens and tunnels to spray drying. Hills (2011) states that pneumatic-conveying ring driers and attrition driers are good but horizontal vibrating fluid-bed driers are perhaps the best (Southward, 2002). This type of drier consist of two levels of perforated trays through which heated air (75 – 115°C) is blown upwards, and which in combination with the shaking of the drier, fluidises the casein. Adjustable weirs at the end of each deck set the product depth for each level. This helps with residence time and level of fluidization. The control point is the outlet temperature. 

The temperature of drying depends on the methods used. If it is a two-stage drying process, the temperature is between 50 and 55ºC in the first stage and then 65ºC in the second stage.

The process of spray drying causes some unavoidable losses in protein functionality. This is due to difficulties with reconstitution as well as the dehydration process that occurs during such an operation which causes aggregation and denaturation (Augustin and Udabage, 2007).

After drying, the rennet casein is white or slightly yellow. The darker the casein, the more inferior it is regarded because it reflects on increasing levels of lactose which have undergone non-enzymatic browning.

Milling and Particle Size Reduction

The dried casein is milled to achieve the desired particle size of either 40, 60 or  80 mesh and consistency. This step is crucial for ensuring uniformity and ease of handling in subsequent processing and applications.

Blending and Formulation

Depending on the intended application, casein may undergo blending with other ingredients or additives to achieve specific properties or functionalities. For example, casein may be blended with other proteins, carbohydrates, or functional additives to enhance its solubility, stability, or nutritional profile.

Packaging and Storage

The final product is packaged into various formats, including bags, drums, or bulk containers, depending on customer requirements. Proper packaging is essential to protect the casein from moisture, oxygen, and contaminants during storage and transportation.

Quality Control

Throughout the manufacturing process, stringent quality control measures are implemented to ensure the consistency, purity, and safety of the casein product. Quality control tests may include analysis of protein content, moisture content, particle size distribution, microbial load, and sensory attributes.

Environmental Considerations

Casein manufacturing facilities also need to address environmental concerns associated with waste disposal and resource consumption. Effluent treatment systems are employed to treat wastewater generated during processing, while energy-efficient practices help minimize the carbon footprint of production operations.

Recent Methods – Electrodialysis

One of the recent methods involves electrodialysis with bipolar membranes (EDBM) that is coupled to ultrafiltration which is a more environmentally friendly method. No chemical treatments are involved. It is a variant of the acid precipitation approach and relies on adjusting the pH to match kappa-caseins pI. The idea was first developed by Bazinet et al.,. A series of papers involved the separation of proteins in the same module using a two-compartment EDBM system. The benefit this had was separating off the casein using acid precipitation whilst the whey is then demineralised.

The large-scale manufacture of casein from milk involves a series of steps including milk reception, separation, coagulation, curd formation, washing, drying, milling, blending, packaging, and quality control. Each step plays a critical role in ensuring the purity, consistency, and functionality of the final casein product, which finds diverse applications in industries such as food, pharmaceuticals, cosmetics, and textiles. Moreover, sustainability and environmental stewardship are increasingly important considerations in modern casein manufacturing, driving innovation in resource utilization and waste management practices.

There are a few commercial practices that improve the use of whey by reducing the salt content using electrodialysis. It is already feasible to use a membrane process such as nanofiltration and ultrafiltration to isolate salt and this can be further enhanced using electrodialysis .

References

Al-Akoum, et al., (2002) Sep. Purif. Technol. 28 pp. 219–234

Augustin, M. A., & Udabage, P. (2007). Influence of processing on functionality of milk and dairy proteins. Advances in Food and Nutrition Research, 53, pp. 1-38.

Bazinet, L., Lamarche, F., Ippersiel, D., & Amiot, J. (1999). Bipolar membrane electroacidification to produce bovine milk casein isolate. Journal of Agricultural and Food Chemistry, 47(12), pp. 5291-5296.

Fox, P. F., & Mulvihill, D. M. (1990). Casein. In Food gels (pp. 121-173). Dordrecht: Springer Netherlands.

Hills, M. (2011). Manufacture of Casein from Milk Retentates (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/8745  .

Scherer, R. (1906 [2015]). Casein: Its preparation and technical utilisation. Scott, Greenwood. Reprinted a number of times.

Selvaggi, M., Tufarelli, V., Ventimiglia, A. M., & Birkenhager, J. M. (2011). Casein: Production, uses and health effects.

US Patent 2468730A (1945)- Method of purifying casein. Block, R.J. & Howard, H.W. The Borden Company. New York USA.

van Slyke, L.L., Bosworth, A.W. (1916) J. Biol. Chem. 24 pp. 191.

____________., Baker, J.C. (1918) The Preparation of Pure Casein. J. Biol. Chem. 35 (1) pp. 127-136 (article)