What is the difference between pasteurised and ultra-pasteurised milk?

According to the U.S. Dairy industry, all milk sold in stores is pasteurised to kill harmful bacteria, but not all pasteurisation methods are equal. Understanding the difference between pasteurised and ultra-pasteurised milk is crucial for consumers who care about shelf life, taste, and nutritional profile.

Quick Summary

This guide compares standard pasteurisation (HTST) and ultra-pasteurisation (UHT), detailing the differences in processing temperature, shelf life, taste, and nutritional changes. It also explores the practical considerations for consumers when choosing between these two milk varieties.

Key Points

• Processing Temperatures: Standard pasteurised milk is heated to a lower temperature (72°C) for longer (15s), while ultra-pasteurised milk is heated to a higher temperature (138°C) for a shorter time (2s).

• Shelf Life: Pasteurised milk lasts about 10-21 days and needs refrigeration. Ultra-pasteurised (UHT) milk, with aseptic packaging, can last for months unrefrigerated until opened.

• Taste: The higher heat of ultra-pasteurisation can give the milk a slightly cooked or sweeter taste, whereas standard pasteurised milk has a fresher flavour.

• Nutritional Impact: While major nutrients like calcium and protein are preserved, ultra-pasteurisation may cause a slightly greater loss of heat-sensitive vitamins like B12 and C compared to standard pasteurisation.

• Storage Convenience: Ultra-pasteurised (UHT) milk is ideal for stocking up or for places with unreliable refrigeration, as it is shelf-stable until opened.

• Culinary Use: The heat treatment of ultra-pasteurised milk can denature proteins, potentially affecting its ability to whip compared to standard pasteurised milk.

Pasteurisation is a heating process developed to eliminate pathogenic bacteria in milk, making it safe for consumption. Over time, this process has evolved, leading to different techniques that result in varying product characteristics, with the most common being High Temperature Short Time (HTST) pasteurisation and Ultra-High Temperature (UHT) pasteurisation, often referred to as ultra-pasteurised milk. While both methods achieve the same goal of enhancing food safety, their distinct temperature and time parameters lead to significant differences in shelf life, taste, and convenience.

The Standard: HTST Pasteurisation

Standard pasteurised milk, typically found in the refrigerated section, undergoes HTST processing.

• The milk is heated to a minimum of 72°C (161°F) for at least 15 seconds, followed by rapid cooling.
• This process effectively kills disease-causing microorganisms like E. coli and Salmonella but leaves some non-pathogenic spoilage bacteria.
• Because some bacteria remain, HTST milk must be continuously refrigerated and has a shorter shelf life, typically lasting 10 to 21 days unopened.
• The flavour profile of HTST milk is closer to fresh, raw milk, with minimal 'cooked' taste.

The Advanced Method: Ultra-Pasteurisation

Ultra-pasteurised (UP) milk, which includes UHT milk, is heated to a much higher temperature for a shorter period.

• The milk is heated to at least 138°C (280°F) for a minimum of two seconds.
• This more intense heat treatment eliminates virtually all bacteria, including those that cause spoilage, making the product nearly sterile.
• This extended shelf life is paired with aseptic packaging for UHT products, allowing them to be stored at room temperature for several months until opened. Ultra-pasteurised milk not in aseptic packaging still requires refrigeration but will last longer than HTST milk.
• The higher temperature can cause a slightly 'cooked,' sweeter, or caramelised flavour that some consumers notice.

Comparing Processing and Product Qualities

Feature	Pasteurised (HTST) Milk	Ultra-Pasteurised (UHT/UP) Milk
Temperature	Min. 72°C (161°F)	Min. 138°C (280°F)
Time	15 seconds	2 seconds
Effect on Bacteria	Kills pathogenic bacteria, some spoilage bacteria remain.	Kills virtually all bacteria, including spoilage organisms.
Shelf Life (Unopened)	10-21 days (refrigerated).	30-90 days (refrigerated for UP) or up to 6 months (room temperature for UHT in aseptic packaging).
Storage	Requires continuous refrigeration.	Refrigerated until opened; UHT milk is shelf-stable until opened.
Taste	Fresh, minimal flavour changes.	Slightly cooked, sweeter, or caramelised taste possible.
Nutritional Impact	Minor loss of heat-sensitive vitamins (B12, C).	Slightly greater loss of heat-sensitive vitamins (B12, C).
Whipping/Baking	Whips well; ideal for applications needing distinct milk solids.	May not whip as well due to protein denaturation.
Availability	Widely available in refrigerated dairy aisles.	Found in refrigerated and shelf-stable sections; often used for organic milk.

The Impact of Ultra-Pasteurisation on Organic Milk

Interestingly, a significant portion of organic milk sold in the U.S. is ultra-pasteurised. This is primarily a logistical decision. Since organic farms can be geographically scattered, UHT processing extends the milk's shelf life and simplifies distribution across wide areas where maintaining a 'cold chain' for HTST milk might be challenging. The extended shelf life minimises spoilage and reduces waste, offering both producers and consumers a practical option.

Considerations for Cooking and Taste

The heat from ultra-pasteurisation denatures the whey proteins in the milk. This can affect its performance in certain culinary applications. For instance, ultra-pasteurised milk may not whip as effectively as HTST milk, and some people find the subtly altered flavour unsuitable for drinking straight. However, this flavour difference is often less noticeable when mixed into coffee, tea, or used in recipes.

Conclusion

The choice between pasteurised and ultra-pasteurised milk boils down to priorities. For those who value the freshest possible taste and have a reliable refrigeration system, standard pasteurised (HTST) milk is the ideal choice. For consumers prioritising convenience, a longer shelf life, and less frequent trips to the store, ultra-pasteurised milk offers a safe and convenient alternative, especially UHT varieties that can be stored in the pantry. Regardless of the option chosen, both processing methods ensure the milk is safe to consume, with minimal differences in major nutritional components like protein and calcium. A good resource for understanding the specifics of different processing methods can be found on Cornell University's College of Agriculture and Life Sciences fact sheet on pasteurisation.

What is the difference between pasteurised and ultra-pasteurised milk?

Frequently Asked Questions

Does ultra-pasteurised milk taste different?

Yes, ultra-pasteurised milk can have a slightly different taste, often described as a little cooked or sweeter due to the higher heat treatment. However, the difference is subtle and not always noticeable, especially when added to other beverages or food.

Do I need to refrigerate ultra-pasteurised milk?

Ultra-pasteurised milk sold in aseptic (hermetically sealed) packaging does not require refrigeration until it is opened. Once opened, it must be refrigerated and has a shelf life similar to regular pasteurised milk, typically 7-10 days.

Which milk is better for baking?

For most baking, either milk type works. However, standard pasteurised milk is often preferred for recipes that rely on milk proteins, such as whipping cream or certain cheeses, because its proteins are less denatured by heat.

Is ultra-pasteurised milk less nutritious?

The overall nutritional difference is minimal. While the higher temperature of ultra-pasteurisation can slightly reduce the levels of heat-sensitive vitamins like B12 and C, the major nutrients such as protein and calcium are largely unaffected.

Why is organic milk often ultra-pasteurised?

Organic milk is often ultra-pasteurised to extend its shelf life. The longer life is beneficial for distribution from smaller, more dispersed organic farms to reach a wider consumer base without spoilage.

Is UHT milk the same as ultra-pasteurised milk?

Ultra-High Temperature (UHT) processing is a form of ultra-pasteurisation. While all UHT milk is ultra-pasteurised, not all ultra-pasteurised milk is UHT. UHT typically refers to the shelf-stable products packaged aseptically, whereas other ultra-pasteurised milk still requires refrigeration.

Is ultra-pasteurised milk safe?

Yes, ultra-pasteurised milk is very safe. The process is specifically designed to kill virtually all bacteria, including harmful pathogens and spoilage organisms, resulting in a product with a high level of microbiological stability.