Effective Methods to Preserve Milk and Dairy Products

Milk is one of the most nutritionally rich foods produced by nature – and that richness is precisely what makes it so vulnerable to spoilage. Proteins, fats, sugars, and minerals create an ideal environment for bacteria, yeasts, and molds to thrive. Without intervention, raw milk can go bad within a few hours at room temperature, sometimes carrying dangerous pathogens like Salmonella, E. coli, and Listeria monocytogenes. To counter this, the dairy industry relies on a range of preservation methods, each targeting microbial growth in a different way. From the cold chain of refrigeration to the intense heat of sterilization – and even the use of radiation and chemical agents – understanding these techniques is essential for anyone working in dairy production, food safety, or quality management.

Why milk spoils – and why preservation matters 🔗

Raw milk is never truly sterile. It picks up microorganisms at every stage – during milking, handling, and transport. Some of these microbes are harmless or even beneficial; others are spoilage agents or outright pathogens. Psychrophilic microorganisms like Pseudomonas and Achromobacter thrive in low-temperature environments and can cause off-flavors and texture changes even in refrigerated milk. Enteric bacteria such as Salmonella, E. coli, and Clostridium perfringens pose direct health risks when present in consumed milk. According to the U.S. Centers for Disease Control and Prevention (CDC), improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food-borne disease source. Preservation methods directly address these threats by either destroying microorganisms, inhibiting their growth, or removing them entirely.

Refrigeration: the first line of defense 🔗

Refrigeration is the most widely used post-production preservation step for milk. It works not by killing bacteria, but by drastically slowing their metabolic activity and reproductive rate. Storing milk at around 4°C (39°F) significantly extends its shelf life after pasteurization, typically to 7-14 days for commercially processed milk. Rapid cooling immediately after milking is equally important – it prevents the initial bacterial load from multiplying before further processing takes place.

However, refrigeration alone is not sufficient for long-term storage. Psychrotrophic bacteria are adapted to survive and even multiply at low temperatures, meaning extended refrigeration without other preservation steps will still lead to spoilage over time. This is why refrigeration is almost always paired with heat treatment rather than used as a standalone method.

Thermisation: the gentle pre-treatment 🔗

Thermisation is a mild heat treatment that occupies the space between raw milk and full pasteurization. Milk is heated to 57-68°C for 15-20 seconds and then rapidly cooled to below 6°C. The primary purpose is to reduce psychrotrophic bacteria and extend the shelf life of raw milk before it undergoes further processing, such as cheese making or concentration.

Importantly, thermisation does not eliminate all pathogens. Research confirms it as an effective heat inactivation strategy that impairs cellular structures and functions of heat-sensitive bacteria, but organisms like Listeria monocytogenes can survive the process. Because thermised milk does not meet the safety standards of pasteurized milk, it cannot legally be labelled as pasteurized in most jurisdictions. It is best understood as a holding strategy – a way to reduce the initial microbial burden of raw milk that will be processed further.

Pasteurization: the cornerstone of dairy safety 🔗

Named after French microbiologist Louis Pasteur, pasteurization has been the foundation of safe milk supply for over a century. It involves heating every particle of milk to a specific temperature for a defined time to inactivate organisms that may cause disease or spoilage. Unlike sterilization, pasteurization does not kill all microorganisms – but it destroys 99.999% of pathogenic bacteria, making milk safe for consumption.

Pasteurization targets organisms such as Mycobacterium tuberculosis, Brucella abortis, Coxiella burnetii, Salmonella, and Listeria. The International Dairy Foods Association (IDFA) recognizes several time-temperature combinations as approved pasteurization methods, each designed to destroy these pathogens while preserving milk’s sensory and nutritional qualities.

Types of pasteurization 🔗

Low Temperature Long Time (LTLT) / Vat pasteurization heats milk to 63°C (145°F) for 30 minutes. It is the gentlest method and is still used in smaller operations and artisan dairy production, though it is less practical for large-scale commercial processing.

High Temperature Short Time (HTST) is the industry standard. Metal plates and hot water raise milk temperature to at least 72°C (161°F) for no less than 15 seconds, followed by rapid cooling. This allows continuous processing of large volumes and produces milk with a typical refrigerated shelf life of 2-3 weeks.

Ultra Pasteurization (UP) heats milk to a minimum of 138°C (280°F) for at least two seconds. It results in a longer shelf life than HTST but still requires refrigeration.

Ultra High Temperature (UHT) takes the process further, heating milk to 135-150°C for 2-5 seconds in commercially sterile equipment, then filling it into aseptically sealed packaging. When combined with aseptic packaging, UHT milk can be stored without refrigeration for up to 9 months, making it valuable for regions with limited cold storage infrastructure.

Sterilization: eliminating all viable organisms 🔗

Sterilization is the most intensive heat treatment applied to milk. It involves the destruction of all living microorganisms and their spores, typically by heating milk to above 110-120°C (230-248°F) for 10-30 minutes in sealed containers. Unlike pasteurization, which targets pathogens and most spoilage organisms, sterilization achieves what is called commercial sterility – the elimination of all organisms capable of growing under normal storage conditions.

In-container sterilization produces shelf-stable milk that requires no refrigeration, but the prolonged high heat causes noticeable changes. Sterilization can alter taste and may cause browning due to Maillard reactions – chemical interactions between proteins and sugars at high temperatures. Some heat-sensitive vitamins, including B vitamins, are also reduced in the process. For this reason, UHT processing (described above) has largely replaced in-container sterilization in modern commercial settings, as the shorter exposure time better preserves flavor and nutrition while still achieving commercial sterility.

A 2025 peer-reviewed study published in Foods notes that while heat pasteurization and sterilization have played a major role in public health, consumer demand for minimally processed and nutrient-retentive products is accelerating interest in alternative technologies.

Irradiation: a non-thermal option 🔗

Food irradiation is a non-thermal preservation technique that uses ionizing radiation – including gamma rays from radioactive isotopes like cobalt-60 or caesium-137, X-rays, or electron beams – to damage the DNA of microorganisms, preventing them from reproducing. With endorsement from international organizations including the FAO and WHO, irradiation is increasingly studied as a method to maintain quality, improve safety, and reduce post-harvest losses in dairy products.

Irradiation does not make food radioactive. Low doses (under 1 kGy) are used to inhibit sprouting or extend shelf life; medium doses (1-10 kGy) reduce spoilage organisms and pathogens. According to FDA guidelines in the United States, irradiated food must carry the label “Treated by irradiation” alongside the international Radura symbol.

However, irradiation has limitations in dairy applications specifically. The adoption of irradiation for dairy products faces strict opposition in many countries, and studies indicate that it can generate undesirable flavors in milk, particularly through oxidation of milk fats. Consumer acceptance also remains low due to misconceptions about the process. As a result, irradiation in dairy is more commonly applied to cheese brine, packaging materials, and dry dairy ingredients rather than fluid milk.

Chemical preservation: agents and applications 🔗

Chemical preservation refers to the use of specific compounds to inhibit microbial growth and extend shelf life. In dairy, chemical preservatives are tightly regulated and used in limited contexts – fresh milk in most markets is not treated with chemical preservatives, both due to regulatory restrictions and consumer expectations of a natural product.

That said, chemical agents play a functional role in certain applications. Hydrogen peroxide (H₂O₂) has historically been used in developing regions where refrigeration is limited. It acts as an oxidizing antimicrobial agent and breaks down into water and oxygen, leaving no residue – though it can affect flavor and reduce certain nutrients. Natamycin, a naturally derived antifungal compound, is applied in cheese production to inhibit mold growth on surfaces without interfering with the bacterial starter cultures responsible for fermentation and flavor development. Nisin, a bacteriocin produced by Lactococcus lactis, is approved in several countries as a preservative for processed cheese and some dairy products, targeting heat-resistant bacteria that may survive pasteurization.

The use of natural antimicrobial agents – plant extracts, essential oils, and lactic acid bacteria – is an active area of research, particularly for artisan and minimally processed dairy products where conventional chemical preservatives are considered inappropriate.

Combining methods: the hurdle technology approach 🔗

In practice, no single preservation method is relied upon exclusively. Modern dairy processing uses what is known as hurdle technology – a strategy of combining multiple preservation barriers to achieve safety and shelf life more effectively than any individual method can alone. Hurdle technology is used to get maximum lethality against microorganisms by combining two or more preservation parameters at optimum levels, which also reduces the need to apply any single method at its most extreme.

Common examples include pasteurized milk that is immediately refrigerated (two barriers: heat and cold), UHT milk packed in aseptic containers (heat treatment plus packaging integrity), and cheese that is thermised, fermented with starter cultures, and then treated with natamycin on the surface. Each additional hurdle targets a different microbial pathway, making the overall system more robust. This layered approach also helps reduce energy use, limit flavor damage, and meet consumer expectations for minimally processed products.

Choosing the right preservation method 🔗

The appropriate preservation method depends on several factors: the intended use of the milk or dairy product, the available infrastructure, the target market, required shelf life, and regulatory requirements. Fluid milk destined for retail in regions with reliable cold chains is typically HTST pasteurized and refrigerated. Products for export, emergency food supplies, or markets with limited refrigeration benefit from UHT or sterilization. Specialty dairy products like artisan cheese may rely on thermisation combined with fermentation and natural antimicrobials.

As research from the UAE University and Beijing Technology and Business University notes, the future of milk processing lies in balancing microbial safety with the preservation of nutritional and sensory quality – a challenge that is driving ongoing interest in non-thermal and emerging technologies like high-pressure processing (HPP) and pulsed electric fields (PEF) as complements to conventional methods.

What do you think? Given that each preservation method involves a trade-off between safety, shelf life, and nutritional quality, which factors should be given the highest priority when choosing how to preserve dairy products – especially in regions with limited cold storage infrastructure? And as non-thermal technologies like irradiation and high-pressure processing become more viable, how should regulatory frameworks evolve to keep up with the science?

References

1. https://www.bivatec.com/blog/milking-hygiene-and-milk-preservation
2. https://en.wikipedia.org/wiki/Pasteurization
3. https://microbenotes.com/preservation-of-milk-and-milk-products/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC10486694/
5. https://ohioline.osu.edu/factsheet/hyg-5817
6. https://www.idfa.org/pasteurization
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC12026572/
8. https://link.springer.com/article/10.1007/s11947-016-1709-y
9. https://www.ebsco.com/research-starters/applied-sciences/pasteurization-and-irradiation
10. https://www.sciencedirect.com/topics/food-science/pasteurization