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Casein Powder Processing: A Guide for Food Processing Consultants and Manufacturers

Q: What pH do we need to hit to precipitate acid casein from skim milk?

Acid casein is formed by acidifying skimmed milk until it reaches the isoelectric point, around pH 4.6. In inorganic acidification, hydrochloric acid is added to bring the pH down to 4.3-4.6 with heating to 40-45°C. Biological acidification instead uses mesophilic cultures held at 25°C, allowing roughly 15 hours for a gradual pH drop to the same range.

Q: Why do most food formulators buy caseinate instead of casein?

Caseinate is used more often than casein in food industries because casein is far less soluble. Acid or rennet casein curd is re-dissolved by reacting it with alkali such as sodium hydroxide, producing sodium caseinate; calcium hydroxide or ammonia yields calcium caseinate. The alkalization step adjusts the product to pH 6.7, which gives the solubility food applications require.

Q: What is the difference between acid casein and rennet casein in production terms?

There are two dry casein types. Acid casein is produced simply by acidifying skimmed milk to the isoelectric point of about pH 4.6. Rennet casein is produced by enzymatic coagulation instead. Both can subsequently be converted to caseinate by reacting the curd or powder with alkali such as sodium hydroxide, which is the more commonly used form in food manufacturing.

Q: What pasteurisation conditions should the skim milk feed see, and why not go hotter?

For casein manufacture, the raw skimmed milk should be pasteurised at 72°C for 15-20 seconds. Use low-fat, properly skimmed milk as the raw material and avoid overheating, because excessive heat treatment darkens the casein and downgrades the finished powder. Holding to the 72°C/15-20 second window protects colour while giving the required microbiological control.

Q: How is whey removed and washed out of the curd before drying?

Decanter centrifuges remove whey efficiently from the casein curd. Washing is then carried out as three-stage counter-current washing at temperatures between 35°C and 60°C. The washed curd leaving this stage reaches roughly 45% dry matter, which is the feed condition for the subsequent hot air drying step.

Q: What drying regime and final moisture should we design for on acid casein powder?

Acid casein is hot air dried to a moisture content of 12%, and two-stage drying is recommended: 50-55°C followed by 65°C. For caseinate, the thinned slurry at 18-24% dry matter is preheated to 80-90°C for sprayability, then spray dried in towers at 200-230°C with fluidized bed dryers, giving a final moisture content of 10-12%.

By PMG Engineering · 21 Apr 2023

Overview

Casein is the primary milk protein, making up nearly 80% of the total nitrogen content in milk. It plays a pivotal role in food processing and nutrition, offering a complete source of essential amino acids. Found predominantly in cow’s milk, casein serves not only the food manufacturing industry but is also extensively used in textile, paint, leather, and paper production.

For any food processing consultant or dairy technologist, understanding the intricacies of casein extraction and processing is crucial to deliver high-quality, shelf-stable protein products.

SEPARATION OF CASEIN

Casein is separated from milk by increasing its acidity, using:

Direct addition of acid (e.g., hydrochloric acid)
Biological fermentation via lactic acid bacteria such as Streptococcus thermophilus and Lactobacillus bulgaricus

The resulting casein curd can be transformed into caseinate by re-dissolving it in alkaline solutions like sodium hydroxide. This is common practice in dairy processing plants and food manufacturing facilities.

DRY CASEIN PRODUCTION:

Two types of caseins are there; Rennet casein and Acid casein.

Acid casein can be easily formed by making the skimmed milk acidic until it reaches the isoelectric point (pH± 4.6). For Rennet casein, the process used will be enzymatic coagulation. Both of these products are created by the effect of a reaction between the acid casein curd and acid casein powder with alkali (sodium hydroxide).

Caseinate is used more often in comparison to casein when it comes to its use in food industries because casein is less soluble than caseinate.

ACID CASEIN

Raw Material

Use low-fat, properly skimmed milk

Ensure pasteurization at 72°C for 15–20 seconds

Avoid overheating to prevent darkened casein

Pasteurizing

The raw skimmed milk should be pasteurized for 15-20 seconds at a temperature of 72deg.c.

Acidification

Inorganic Acidification: Add HCl to reduce pH to 4.3–4.6 and heat to 40–45°C

Biological Acidification: Add mesophilic cultures; maintain 25°C and allow 15 hours for gradual pH drop

Decanter and Washing

Decanter centrifuges remove whey efficiently

Use three-stage counter-current washing at 35°C to 60°C

Final product: ~45% dry matter

Drying

Hot air drying to reduce moisture content to 12%

Two-stage drying recommended: 50–55°C followed by 65°C

Grinding

Final casein powder is ground to sizes of 0.32mm, 0.42mm, or 0.64mm

Thinning

Rehydrate acid casein to 18–24% dry matter

Wet grind at <45°C to avoid agglomeration

Preheating and Drying

Preheat to 80–90°C for sprayability
Use spray drying towers (200–230°C) and fluidized bed dryers
Final moisture content: 10–12%

Alkalization and pH Control

Adjust to pH 6.7 using:

Sodium hydroxide for sodium caseinate
Calcium hydroxide/ammonia for calcium caseinate

Conclusion

The processing of casein powder—from separation and drying to conversion into caseinates—plays a critical role in the food manufacturing and dairy industries. With its high nutritional value, slow digestion rate, and wide industrial applications, casein is more than just a protein—it’s a strategic ingredient in both food product development and nutraceutical innovation.

For any food consultant, food processing consultant, or engineering consultancy involved in dairy plant design or protein ingredient optimization, understanding the nuances of acid and rennet casein production is essential. When coupled with hygienic plant design and precise process control, casein manufacturing offers opportunities to enhance product quality, extend shelf life, and meet global food safety standards.

By leveraging expert insights and adhering to engineering best practices, businesses can achieve operational efficiency while delivering high-quality dairy proteins that meet the evolving demands of the global food market.

Reference

Tetra Pak Dairy Handbook

GEA Casein Production Line

ScienceDirect: Casein

YouTube Video

Frequently asked

What pH do we need to hit to precipitate acid casein from skim milk?

Acid casein is formed by acidifying skimmed milk until it reaches the isoelectric point, around pH 4.6. In inorganic acidification, hydrochloric acid is added to bring the pH down to 4.3-4.6 with heating to 40-45°C. Biological acidification instead uses mesophilic cultures held at 25°C, allowing roughly 15 hours for a gradual pH drop to the same range.

Why do most food formulators buy caseinate instead of casein?

Caseinate is used more often than casein in food industries because casein is far less soluble. Acid or rennet casein curd is re-dissolved by reacting it with alkali such as sodium hydroxide, producing sodium caseinate; calcium hydroxide or ammonia yields calcium caseinate. The alkalization step adjusts the product to pH 6.7, which gives the solubility food applications require.

What is the difference between acid casein and rennet casein in production terms?

There are two dry casein types. Acid casein is produced simply by acidifying skimmed milk to the isoelectric point of about pH 4.6. Rennet casein is produced by enzymatic coagulation instead. Both can subsequently be converted to caseinate by reacting the curd or powder with alkali such as sodium hydroxide, which is the more commonly used form in food manufacturing.

What pasteurisation conditions should the skim milk feed see, and why not go hotter?

For casein manufacture, the raw skimmed milk should be pasteurised at 72°C for 15-20 seconds. Use low-fat, properly skimmed milk as the raw material and avoid overheating, because excessive heat treatment darkens the casein and downgrades the finished powder. Holding to the 72°C/15-20 second window protects colour while giving the required microbiological control.

How is whey removed and washed out of the curd before drying?

Decanter centrifuges remove whey efficiently from the casein curd. Washing is then carried out as three-stage counter-current washing at temperatures between 35°C and 60°C. The washed curd leaving this stage reaches roughly 45% dry matter, which is the feed condition for the subsequent hot air drying step.

What drying regime and final moisture should we design for on acid casein powder?

Acid casein is hot air dried to a moisture content of 12%, and two-stage drying is recommended: 50-55°C followed by 65°C. For caseinate, the thinned slurry at 18-24% dry matter is preheated to 80-90°C for sprayability, then spray dried in towers at 200-230°C with fluidized bed dryers, giving a final moisture content of 10-12%.

CITE THIS

PMG Engineering. (2023). Casein Powder Processing: A Guide for Food Processing Consultants and Manufacturers. PMG Engineering. https://pmg.engineering/Article/177/casein-powder-processing-a-guide-for-food-processing-consultants-and-manufacturers/

https://pmg.engineering/Article/177/casein-powder-processing-a-guide-for-food-processing-consultants-and-manufacturers/