The Comprehensive Guide to the Process Used to Preserve Milk

January 2, 2026 •

4 min read

Milk is a highly perishable food that can spoil within a few hours at room temperature if left untreated. Understanding the process used to preserve milk is crucial for ensuring food safety, extending its shelf life, and making dairy products accessible worldwide. This guide explores the scientific principles and common techniques involved in keeping milk safe and fresh for longer.

Quick Summary

Milk preservation extends shelf life and ensures safety by controlling microorganisms. Key techniques involve heat treatments like pasteurization and UHT, as well as methods that remove water or use low temperatures. These processes destroy harmful bacteria, inactivate enzymes, and protect against spoilage, making milk and its products safe for consumption and distribution.

Key Points

Pasteurization is a heat treatment: It uses specific time and temperature combinations (e.g., HTST) to kill harmful pathogens and extend refrigerated shelf life.
UHT processing makes milk shelf-stable: Heating milk to very high temperatures for a few seconds kills all microorganisms, enabling long-term storage without refrigeration.
Drying and evaporation remove moisture: These methods reduce the water content to inhibit microbial growth, creating shelf-stable products like milk powder and condensed milk.
Low temperatures slow spoilage: Refrigeration and freezing inhibit microbial and enzymatic activity, delaying milk spoilage.
Non-thermal methods are emerging: Technologies like High-Pressure Processing and Pulsed Electric Fields inactivate microbes with minimal heat, preserving more nutrients and fresh flavor.
All methods prioritize food safety: Regardless of the technique, the primary purpose of preserving milk is to destroy disease-causing microorganisms and ensure it is safe for human consumption.

Milk preservation is a cornerstone of the modern dairy industry, transforming a highly perishable raw product into a safe, nutritious staple with an extended shelf life. The primary goal is to neutralize pathogenic bacteria that can cause illness and to minimize spoilage-causing microbes and enzymes. This is achieved through a variety of methods, predominantly thermal processing, but also includes methods involving moisture removal and refrigeration.

Heat Treatment Methods: Pasteurization and Sterilization

Heat treatment is the most common method for preserving milk and is named after French scientist Louis Pasteur, who discovered that heating liquids could kill harmful microorganisms.

Pasteurization

This is a mild heat treatment that targets pathogenic organisms like E. coli and Salmonella, but does not eliminate all bacterial spores. Pasteurization significantly extends the refrigerated shelf life of milk from a few hours to several weeks. The most common forms are:

High-Temperature Short-Time (HTST): The milk is heated to 72–75°C for 15–30 seconds before being rapidly cooled. This is the standard method for most retail milk and must be kept refrigerated.
Low-Temperature Long-Time (LTLT): Also known as vat pasteurization, this method heats milk to 63°C for 30 minutes. It is now mostly used for smaller batches or for products like ice cream mix.

Ultra-High Temperature (UHT) Processing

For milk that is shelf-stable and does not require refrigeration before opening, UHT processing is used. This involves:

Heating milk to a very high temperature (135–150°C) for just a few seconds.
This intense heat kills all bacteria and spores, achieving commercial sterility.
The milk is then packaged aseptically, meaning in a sterilized container within a sterile environment, to prevent recontamination.

Moisture Removal: Concentrated and Dried Milk

Reducing the water content of milk creates a much less hospitable environment for microbial growth, extending its shelf life dramatically.

Evaporation and Condensation

In this process, milk is first heated and then concentrated by removing a significant portion of its water content. Two products result from this method:

Evaporated Milk: Approximately 60% of the water is removed, and the product is sterilized by heating in the can.
Sweetened Condensed Milk: A high concentration of sugar is added during the evaporation process. This, along with the reduced water content, inhibits microbial growth, allowing the product to last for years without refrigeration.

Drying into Milk Powder

Milk powder is made by removing almost all moisture from the milk. The two main methods are spray drying and drum drying.

Spray Drying: Concentrated milk is sprayed as a fine mist into a hot chamber, where the water evaporates almost instantly, leaving a fine powder. This is the most common method for producing high-quality milk powder.
Drum Drying: A thin layer of milk is applied to a heated drum, where it dries and is then scraped off as a solid sheet, which is ground into powder. This method can produce a slightly 'cooked' flavor.

Comparison of Key Milk Preservation Methods


Feature	Pasteurization (HTST)	UHT Processing	Evaporation	Drying (Milk Powder)
Primary Mechanism	Moderate heat to kill pathogens and spoilage organisms.	Intense heat to achieve commercial sterility.	Removal of water; some use of heat and sugar.	Almost complete removal of water.
Shelf Life	~2-3 weeks (refrigerated).	~6-9 months (ambient).	~Several months (ambient).	~Up to 2 years (ambient).
Storage Requirement	Refrigeration required.	No refrigeration needed before opening.	No refrigeration needed before opening.	No refrigeration needed.
Nutritional Impact	Minor changes; most nutrients retained.	Slight reduction in some heat-sensitive vitamins (e.g., Vitamin C).	Minor changes in most nutrients.	Good retention of nutrients.
Flavor Impact	Minimal effect on fresh taste.	Can develop a slightly 'cooked' flavor over time.	Distinct caramelized flavor.	Can have a 'cooked' flavor depending on method.
Primary Use Case	Fresh liquid milk for direct consumption.	Long-life liquid milk for convenience or areas lacking refrigeration.	Concentrated liquid for cooking and baking.	Reconstituted milk, baking, and confectionery.

Low-Temperature Methods

Low temperatures are used to slow the growth of microorganisms and their enzymatic activity, extending the freshness of milk.

Refrigeration: Storing milk at temperatures of 4°C or lower significantly inhibits bacterial growth and is a critical step for pasteurized products.
Freezing: Freezing milk can preserve it for several months, although it can cause changes in texture and taste due to fat separation upon thawing. This method is less common for commercially sold fluid milk but is viable for home storage.

Other Preservation Techniques

Fermentation

Fermentation uses beneficial microorganisms, like lactic acid bacteria, to convert lactose into lactic acid. This process lowers the pH of the milk, creating an acidic environment that inhibits the growth of harmful bacteria and extends the shelf life of products like yogurt and kefir.

Non-Thermal Processing

Innovative technologies are emerging to preserve milk with minimal impact on its nutritional and sensory qualities.

High-Pressure Processing (HPP): Uses extreme pressure (400–600 MPa) instead of heat to kill microorganisms, while better retaining the fresh taste and nutrients.
Pulsed Electric Fields (PEF): Applies short bursts of high-voltage electric fields to disrupt microbial cell membranes.
Microfiltration: Physically removes bacteria and spores by passing milk through a ceramic membrane.

Conclusion

From ancient practices to modern technology, the process used to preserve milk has evolved significantly to meet global demands for safety, convenience, and quality. Pasteurization remains the gold standard for fresh milk, while UHT and moisture removal methods provide shelf-stable options that facilitate wider distribution. Meanwhile, cutting-edge, non-thermal techniques like HPP and PEF continue to be developed, offering promising new ways to maintain the integrity of milk without relying on intense heat. The continued focus on hygienic processing, rapid cooling, and innovative preservation methods ensures a safe and nutritious milk supply for consumers around the world.

Frequently Asked Questions

The primary method is High-Temperature Short-Time (HTST) pasteurization. This involves heating milk to 72–75°C for 15–30 seconds before rapidly cooling it, which kills harmful bacteria and extends its refrigerated shelf life to several weeks.

No, pasteurization has a minimal effect on the nutritional value of milk. While UHT can slightly reduce some heat-sensitive vitamins like C, the core nutrients such as protein and calcium are not significantly impacted by the heat treatments used for preservation.

UHT milk does not need refrigeration because the Ultra-High Temperature (UHT) process kills all microorganisms and their spores, making the milk commercially sterile. It is then packaged in a sterile, airtight container that prevents recontamination.

Yes, you can extend the shelf life of milk at home by heating it (scalding) to 82°C (180°F) or by freezing it. Freezing can alter the texture, but it remains safe to use, especially for cooking.

No, it is not recommended to drink raw milk. Raw milk can harbor dangerous bacteria like Salmonella, E. coli, and Listeria, which can cause serious foodborne illness. The CDC attributes most dairy-related disease outbreaks to raw milk products.

HPP is an emerging, non-thermal preservation method that uses extremely high pressure to inactivate microbes and pathogens. It is favored for its ability to extend shelf life while better preserving the fresh flavor and nutrients compared to traditional heat methods.

Frozen milk can be safely stored for several months, but the texture may change upon thawing due to fat separation. It's best to thaw it in the refrigerator and shake it well before using.