Casein is the primary protein found in milk, making up about 3 percent of cow's milk. It is an amorphous white solid that is tasteless and odorless in its pure form. Casein is a phosphoprotein and exists as a complex of several similar proteins within milk. It can be precipitated from milk using acid or the enzyme rennet. This property is utilized in the production of cheese, where rennet causes milk to curdle. Casein also serves as a binder and adhesive and is used in various applications, including paints, glues, plastics, and even man-made fibers.

Where is casein commonly found?

Casein is primarily found in milk , making it the chief protein in milk and the essential ingredient in cheese . Cow's milk typically contains about 3 percent casein. This phosphoprotein is also used in various products, including paints, adhesives, medicines, dietary supplements, and cosmetics. Minor industrial applications include leather treatment, cleaners, textile printing, insecticide sprays, and soapmaking. Casein is also a component in paper coatings, glues, plastics, and man-made fibers.

How does casein compare to other milk proteins, like whey?

Casein and whey are the two primary proteins found in milk, but they differ significantly in their properties and how they are processed. Casein, which constitutes about 75% of milk protein, is a phosphoprotein that precipitates when milk sours or is treated with rennet, forming curds essential for cheese production. It is insoluble in water and is used in various applications, including paints, adhesives, and plastics. Whey, on the other hand, is the watery liquid remaining after casein has coagulated and been removed. It contains water-soluble proteins like alpha-lactalbumin and beta-lactoglobulin, along with lactose, minerals, and trace fats. Whey is often processed into powders for use in food products, baking, and candy making. While casein is known for its slow digestion rate, whey proteins are rapidly absorbed.

What happens to casein when milk is processed into cheese?

When milk is processed into cheese, the primary protein, casein , undergoes a transformation. Casein is coagulated, causing it to clump together and form solid curds, separating from the liquid whey. This curdling process is typically initiated by adding starter cultures that produce lactic acid, and often a coagulant like rennet. The casein then precipitates out of solution, forming the basis of the cheese. This curd is then further processed, drained, salted, and aged to develop the final cheese product.

Are there any health concerns or allergies related to casein?

Casein is a protein found in milk, and while it's a common allergen, it's important to distinguish between a casein allergy and lactose intolerance. A casein allergy is an immune system response to the protein itself, which can cause symptoms ranging from hives and digestive upset to severe anaphylaxis. Lactose intolerance, on the other hand, is the inability to digest lactose, the sugar in milk, leading to digestive discomfort but not an immune reaction. Individuals with a diagnosed casein allergy must avoid all dairy products.

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Top Questions

What is casein?
Casein is the primary protein found in milk, making up about 3 percent of cow's milk. It is an amorphous white solid that is tasteless and odorless in its pure form. Casein is a phosphoprotein and exists as a complex of several similar proteins within milk.

It can be precipitated from milk using acid or the enzyme rennet. This property is utilized in the production of cheese, where rennet causes milk to curdle. Casein also serves as a binder and adhesive and is used in various applications, including paints, glues, plastics, and even man-made fibers.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Where is casein commonly found?
Casein is primarily found in milk, making it the chief protein in milk and the essential ingredient in cheese. Cow's milk typically contains about 3 percent casein. This phosphoprotein is also used in various products, including paints, adhesives, medicines, dietary supplements, and cosmetics. Minor industrial applications include leather treatment, cleaners, textile printing, insecticide sprays, and soapmaking. Casein is also a component in paper coatings, glues, plastics, and man-made fibers.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does casein compare to other milk proteins, like whey?
Casein and whey are the two primary proteins found in milk, but they differ significantly in their properties and how they are processed. Casein, which constitutes about 75% of milk protein, is a phosphoprotein that precipitates when milk sours or is treated with rennet, forming curds essential for cheese production. It is insoluble in water and is used in various applications, including paints, adhesives, and plastics.

Whey, on the other hand, is the watery liquid remaining after casein has coagulated and been removed. It contains water-soluble proteins like alpha-lactalbumin and beta-lactoglobulin, along with lactose, minerals, and trace fats. Whey is often processed into powders for use in food products, baking, and candy making. While casein is known for its slow digestion rate, whey proteins are rapidly absorbed.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What happens to casein when milk is processed into cheese?
When milk is processed into cheese, the primary protein, casein, undergoes a transformation. Casein is coagulated, causing it to clump together and form solid curds, separating from the liquid whey. This curdling process is typically initiated by adding starter cultures that produce lactic acid, and often a coagulant like rennet. The casein then precipitates out of solution, forming the basis of the cheese. This curd is then further processed, drained, salted, and aged to develop the final cheese product.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Are there any health concerns or allergies related to casein?
Casein is a protein found in milk, and while it's a common allergen, it's important to distinguish between a casein allergy and lactose intolerance. A casein allergy is an immune system response to the protein itself, which can cause symptoms ranging from hives and digestive upset to severe anaphylaxis. Lactose intolerance, on the other hand, is the inability to digest lactose, the sugar in milk, leading to digestive discomfort but not an immune reaction. Individuals with a diagnosed casein allergy must avoid all dairy products.
1 Britannica Source
1. Milk - Con 3: Dairy milk is bad for human health.
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

casein, the chief protein in milk and the essential ingredient of cheese. In pure form, it is an amorphous white solid, tasteless and odourless, while its commercial type is yellowish with a pleasing odour. Cow’s milk contains about 3 percent casein.

Properties

Pure casein is an amorphous white solid without taste or odour. Commercial casein is slightly yellow, with a pleasant odour. Dry casein keeps well if protected from insects and rodents; damp casein is quickly attacked by molds and bacteria and acquires a disagreeable odour. The specific gravity is 1.25 to 1.31. Casein is a mixture of phosphoproteins of differing molecular weight.

Casein is a lyophilic colloid akin to albumin and gelatin. It is isoelectric at pH 4.6 where its solubility in water is but 0.01 percent. It is amphoteric: below pH 4.6 casein forms moderately soluble salts such as casein chloride; above pH 4.6 casein forms salts with bases. Sodium caseinate and other alkali salts are soluble without limit, while calcium caseinate, other alkaline earth salts, and heavy metal salts are nearly insoluble. Caseinates readily form gels when slowly coagulated from concentrated solutions. Formaldehyde forms an insoluble compound with casein. Casein is insoluble in most organic solvents. Paracasein is less lyophilic but otherwise identical with casein.

Manufacture

Casein is usually made from skim milk (rarely from buttermilk), by one of three methods: (1) naturally soured casein curdles when enough lactic acid develops from fermentation of milk sugar by the ever present bacterium Streptococcus lactisi; (2) acid casein is precipitated by adding dilute hydrochloric acid or sulfuric acid; (3) for rennet casein, warm skim milk is set with rennet extract until the calcium paracaseinate clots, after which the clot is cut into small pieces to allow the whey to drain. In all three methods the whey is drawn off, the curd washed with water, drained or pressed, dried in warm air, ground, and packed for sale. Rennet casein retains much of the calcium phosphate from the milk.

Uses

Casein is used in prepared foods, in medicines and dietary supplements, and in cosmetics. Minor industrial applications include the seasoning and dressing of leather, cleaners and polishes for shoes, textile printing and sizing, insecticide sprays, soapmaking, and many uses in which casein serves as a protective colloid, emulsifying agent, or binder. Major applications of casein are paper coatings, glues, paints, plastics, and man-made fibres.

Paper coatings

Book and art papers are coated with pigmented casein to provide a suitable surface for half-tone illustrations. A moderately alkaline solution of naturally soured or acid casein is mixed with a water slurry of the pigments. Formaldehyde or lime may be added for better resistance to water. The mixture is spread on the paper in a coating machine and dried.

Glues

Wood joints made with casein glue withstand dampness for some time. Prepared casein glue is a powder composed of naturally soured or acid casein, lime, suitable sodium salts, and a fungicide. The powder is dissolved in water shortly before the glue is used, whereupon the sodium salts precipitate part of the lime, release sodium hydroxide, and dissolve the casein as sodium caseinate; later the rest of the lime slowly changes the sodium caseinate to insoluble calcium caseinate.

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Paints

Casein paints or distempers provide moderately washable, lustreless decoration for interior walls or for exterior masonry. Casein powder paints, to be mixed with water, are similar to casein glue in composition except for the further addition of pigments. Casein paste paints, to be diluted with water, are made by pigmenting weakly alkaline solutions of casein. Casein is also used as the emulsifying agent in emulsion paints, which are oil paints that can be thinned with water.

Plastics

Molded plastics of casein resemble horn, ivory, ebony, and marble in appearance. The principal use is for buttons for clothing. Rennet casein is granulated, moistened with water, and kneaded thoroughly. Dyes or pigments may be added. The granules absorb the water and are softened. The material is then passed through a heated cylinder press with rotating screw from which soft plastic is extruded under pressure in rods or tubes. The soft plastic may then be molded in the desired shape. The shaped plastic is hardened by long soaking in formaldehyde solution after which it is slowly dried.

Human-made fibres

Wool-like textile fibres are made from casein by extruding an alkaline solution of casein through spinnerets of the kind used in making rayon and then hardening the fibres in an acid bath containing formaldehyde. First marketed in the 1930s under the name Lanital in Italy and Aralac in the United States, human-made casein fibres saw use during World War II due to wool shortages. There was renewed interest in casein fibre in the 21st century as manufacturers sought to explore sustainable alternatives to petroleum-based synthetic fibres such as nylon.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Meg Matthias.

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Manufacture

Uses

Paper coatings

Glues

Paints

Plastics

Human-made fibres