Production and Processing of Milk and Dairy Products

Milk is one of nature’s most complete foods, providing an impressive array of nutrients that support human health across all life stages. From the farm to your refrigerator, milk undergoes a carefully controlled journey involving specific production practices and processing techniques that ensure both safety and quality. Understanding this journey-from milking to the creation of cream, butter, cheese, and ice cream-offers fascinating insight into one of the world’s oldest and most essential food industries.

The nutritional value of milk 🔗

Milk delivers a powerful combination of essential nutrients in every glass. It contains high-quality proteins, including casein and whey proteins, that support muscle growth and repair. The fat content provides energy and helps absorb fat-soluble vitamins A, D, and E. Milk is also rich in calcium and phosphorus for bone health, along with B vitamins essential for energy metabolism.

Milk solids include both fat and non-fat components-proteins, lactose (milk sugar), and minerals. These components form the foundation for all dairy products. The composition of milk can vary based on the animal species, breed, diet, and lactation stage, which is why standardization becomes an important step in commercial processing.

Market milk production: From farm to processing plant 🔗

The journey of market milk begins with strict hygiene practices at the dairy farm. Modern dairy operations use vacuum-powered milking machines with cups attached to cow teats. The milk travels through stainless steel pipes directly to refrigerated storage tanks, where it is rapidly cooled to 5°C (41°F) or below to prevent bacterial growth.

In the United States, the Grade “A” Pasteurized Milk Ordinance (PMO) has served as the foundation for milk safety standards since 1924. This comprehensive regulation covers everything from dairy farm design and milking area sanitation to processing, transportation, and storage requirements. The ordinance essentially provides a “cow-to-cup” strategy for product safety assurance.

The importance of clean practices 🔗

Milk quality depends heavily on conditions at the dairy farm. Milk from animals undergoing antibiotic treatment cannot be used for processing, as antibiotics interfere with the bacterial cultures needed for making cheese and other fermented products. Feeding animals poorly prepared silage can also adversely affect the quality of various cheese varieties.

Upon arrival at processing plants, milk undergoes testing for freshness, bacterial counts, and composition before being accepted. This quality control ensures only safe, high-quality milk enters the production chain.

Pasteurization: Making milk safe 🔗

Pasteurization is the cornerstone of milk safety. This process involves heating milk to a specific temperature for a set period to eliminate harmful bacteria without significantly altering nutritional value or taste.

The most common methods include:

High-Temperature Short-Time (HTST) pasteurization: Milk is heated to at least 72°C (161°F) for 15 seconds. This is the standard method for most commercial milk.

Ultra-High Temperature (UHT) processing: Milk is heated to 135-150°C (275-302°F) for 1-2 seconds. This produces shelf-stable milk that can be stored without refrigeration until opened.

Pasteurization effectively destroys pathogens including Listeria, Salmonella, Campylobacter, and E. coli. The FDA strongly supports pasteurization as an effective measure to protect food safety, noting that since 1987, there have been over 143 reported illness outbreaks associated with raw milk consumption.

Homogenization: Creating consistency 🔗

If you have ever noticed that cream rises to the top of unhomogenized milk, you understand the purpose of homogenization. This mechanical process reduces fat globule size from an average of 3.5 micrometers to below 1 micrometer, preventing fat separation and creating a uniform product.

During homogenization, milk is forced under high pressure (typically 2,500-3,000 psi) through a narrow gap no wider than a human hair. The disintegration of fat globules occurs through a combination of turbulence and cavitation as milk passes through at high velocity.

The benefits of homogenization extend beyond convenience. Homogenized milk has improved colour, mouthfeel, and digestibility. The process also ensures emulsifiers and stabilizers are evenly distributed throughout the product. Importantly, homogenization does not change milk’s nutritional value-it simply improves texture and prevents cream-line formation.

Cream and butter production 🔗

Cream is separated from whole milk using centrifugal separators that exploit the density difference between fat and the aqueous milk phase. The resulting cream typically contains 35-40% milk fat and serves as the starting material for butter production.

The butter-making process 🔗

Butter production transforms cream from an oil-in-water emulsion to a water-in-oil emulsion through churning. The process begins with cream pasteurization at higher temperatures than fluid milk (typically 85°C/185°F for 15 seconds) to destroy enzymes and microorganisms that could affect keeping quality.

The cream is then tempered-cooled to an optimal churning temperature between 10-15°C (50-59°F)-and held for several hours to allow proper fat crystallization. During churning, physical agitation causes fat globules to collide and aggregate, eventually forming butter grains while releasing buttermilk.

Modern creameries use either batch churns or continuous butter-making machines. The churning process takes 30-45 minutes, during which the cream undergoes several phases-from foamy to grainy as butter separates from buttermilk. After draining the buttermilk, the butter is worked (kneaded) to form a cohesive mass, salted if desired, and packaged. The final product contains approximately 80% milk fat and 16% water.

Cheese making: An ancient art meets modern science 🔗

Cheese making represents one of humanity’s oldest food preservation techniques. The fundamental process involves removing water from milk while retaining most of the solids, extending shelf life through controlled fermentation.

Essential steps in cheese production 🔗

The cheese-making process follows several key stages. First, milk is standardized to achieve the desired fat-to-protein ratio and pasteurized (though some traditional cheeses use raw milk that must be aged at least 60 days). Starter cultures are added to ferment lactose into lactic acid, lowering the pH and beginning flavour development.

Rennet, an enzyme traditionally obtained from calf stomachs but now often produced through fermentation, is then added. Rennet causes casein proteins to form chains that develop into a gel-like network, trapping water and fat. This semisolid gel-the curd-is cut into small pieces to release whey.

The curds are cooked, stirred, and drained of whey. Temperature during cooking affects the final cheese texture. Curds are then salted (through dry salting, surface application, or brine soaking) and pressed into moulds. Finally, cheese is aged under controlled temperature and humidity conditions, during which bacteria, yeasts, and moulds transform the curd into cheese with characteristic flavours, textures, and aromas.

Ice cream: The frozen dairy treat 🔗

Ice cream production combines dairy science with the physics of freezing to create a product that is simultaneously creamy, cold, and flavourful. According to U.S. standards, ice cream must contain at least 10% milk fat and 20% total milk solids.

Manufacturing process 🔗

Ice cream begins as a blend of dairy products (cream, milk, condensed milk), sweeteners, stabilizers, emulsifiers, and flavourings. This mix is pasteurized and then homogenized to reduce fat globule size, creating a smoother, creamier finished product.

After homogenization, the mix is cooled and aged for 4-24 hours at around 5°C. During aging, fat partially crystallizes and proteins hydrate, improving whipping properties. The mix then enters continuous freezers where it is rapidly frozen while air is incorporated. This air incorporation-called overrun-can add up to 50% of the ice cream’s volume, contributing to lightness and affecting texture.

When ice cream exits the freezer at approximately -5°C, only about 50% of the water is frozen. Particulate ingredients like nuts, fruit, and candy pieces are added at this stage. The product is then hardened at -30°C to -40°C, freezing the remaining water and stabilizing the structure for storage.

Concentrated and dried milk products 🔗

Removing water from milk creates products with extended shelf life and reduced transportation costs. Evaporated milk has approximately 60% of its water removed, then is homogenized, canned, and heat sterilized. The high-heat process creates a slightly caramelized flavour and tan colour.

Sweetened condensed milk takes a different preservation approach. After evaporation under vacuum at 65-70°C, sugar is added to increase osmotic pressure, preventing microbial growth without requiring sterilization. This product has a shelf life of approximately two years.

Milk powder production 🔗

Dried milk offers the longest shelf life among milk products. The process involves first concentrating milk to approximately 50% solids through evaporation, then spray drying-spraying the concentrate into a heated chamber where water instantly evaporates, leaving fine powder particles.

Spray-dried milk powder retains nutritional value while reducing weight to roughly one-eighth of the original milk. Drum drying offers an alternative method, but produces powder with a more cooked flavour due to greater heat exposure. These products serve both consumer markets and industrial applications in confectionery, baking, and infant formula manufacturing.

What do you think? How has your understanding of dairy processing changed after learning about the science behind everyday products like butter and cheese? Which dairy product’s manufacturing process surprised you most?

References

1. https://www.milkfacts.info/Milk%20Processing/Ice%20Cream%20Production.htm
2. https://www.fda.gov/consumers/consumer-updates/keeping-your-milk-safe-grass-glass
3. https://www.fda.gov/food/milk-guidance-documents-regulatory-information/pasteurized-milk-ordinance-centennial
4. https://dairyprocessinghandbook.tetrapak.com/chapter/cheese
5. https://www.fda.gov/food/buy-store-serve-safe-food/raw-milk-questions-answers
6. https://www.fda.gov/food/buy-store-serve-safe-food/food-safety-and-raw-milk
7. https://www.usdairy.com/news-articles/what-is-homogenized-milk
8. https://dairyprocessinghandbook.tetrapak.com/chapter/homogenizers
9. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/homogenized-milk
10. https://www.cdr.wisc.edu/butter-science-101
11. https://dairyprocessinghandbook.tetrapak.com/chapter/butter
12. https://www.dairysafe.vic.gov.au/consumers/dairy-foods/butter
13. https://www.britannica.com/topic/cheese-making
14. https://www.usdairy.com/news-articles/how-is-cheese-made
15. https://pubs.nmsu.edu/_e/E216/
16. https://dairy-products-from-france.com/cheese/production/
17. https://teagasc.ie/rural-economy/rural-development/diversification/production-of-ice-cream/
18. https://encyclopedia.che.engin.umich.edu/ice-cream/
19. https://en.wikipedia.org/wiki/Evaporated_milk
20. https://dairyprocessinghandbook.tetrapak.com/chapter/condensed-milk
21. https://en.wikipedia.org/wiki/Powdered_milk
22. https://books.lib.uoguelph.ca/dairyscienceandtechnologyebook/chapter/concentrated-and-dried-dairy-products/