UHT TEMPERATURES OF MILK

UHT PROCESSING OF MILK

PRINCIPLES, APPLICATIONS, AND STANDARDS IN SOUTH AFRICAN DAIRY PRODUCTION.

1. Introduction
Ultra-High Temperature (UHT) processing is a modern heat-treatment technology designed to extend the shelf-life of milk by destroying all pathogenic and spoilage microorganisms, including bacterial spores. The process ensures safety, stability, and convenience without requiring refrigeration before opening. It has become a cornerstone of the dairy industry globally and is widely implemented in South Africa due to its efficiency and adaptability to local conditions.

2. UHT Processing: Temperature and Time Parameters
UHT milk treatment involves heating the milk to very high temperatures for a very short time, ensuring sterilisation while minimising nutrient loss and flavour changes. 

Heat Treatment Method

Temperature (ºC)

Time (sec./min.)

Purpose / Result

Thermisation

63 – 65 ºC

15 sec

Reduces microbial load before storage or further processing

Pasteurisation (LTLT)

63 ºC

13 min

Kills most pathogenic bacteria

HTST (High Temperature, Short Time)

72 – 75 ºC

15 – 20 sec

Widely used for fresh pasteurised milk

Ultra Pasteurisation (Extended Shelf-life)

125 – 138 ºC

2 – 4 sec

Extends shelf-life to several weeks

UHT (Flow Sterilisation)

135 – 150 ºC

2 – 5 sec

Achieves commercial sterility and 6 – 9 months shelf-life

In practice, the most common condition is 137 - 142 ºC for 4 - 6 seconds, depending on the equipment type, milk composition, and desired shelf-life.

3. Process Description
The UHT process typically follows these steps:
1. Preheating - Milk is preheated to 80 ºC to reduce viscosity and prepare for sterilisation.
2. Rapid Heating - The temperature is raised to 135 - 150 ºC using either:
      * Indirect Heating (plate or tubular heat exchangers), or
      * Direct Heating (steam injection or steam infusion).
3. Holding - Milk is held at the target temperature for 2 - 5 seconds.
4. Rapid Cooling - Immediately cooled to below 20 ºC to prevent chemical changes.
5. Aseptic Packaging - Filled into sterile containers in a closed, aseptic environment to prevent recontamination.

This process achieves commercial sterility, meaning the milk is free of viable microorganisms capable of growing under normal storage conditions.

4. Industry Guidelines for UHT Processing
Key principles for effective UHT milk production include:
* Temperature Range: 135 - 150 ºC for 2 - 5 seconds (commonly 137 - 142 ºC).
* System Type: The process must occur in a closed system to prevent contamination.
* Product Considerations: Low-acid product (pH > 4.5, such as milk) required full UHT treatment for safety.
* Quality Factors: Raw milk quality, pH, enzyme stability, and microbial load directly affect the efficiency and outcome of UHT treatment.

Both direct and indirect heating systems are widely used depending on energy efficiency, equipment availability, and desired product characteristics.

5. Application in South African Dairy Production
In South Africa, UHT milk production is well-established and regulated. Leading processors produce UHT milk for nationwide distribution due to its long shelf-life and convenience.

1. Industry Context
UHT milk dominates the South African retail market because:
* It remains shelf-stable for up to 9 months unopened at room temperature.
* It is ideal for regions with limited refrigeration or cold chain capacity.
* It significantly reduces spoilage and distribution losses, especially in rural and export supply chains.

2. Regulatory Framework
UHT processing and labelling in South Africa are governed by:
* The Dairy Products and Imitation Dairy Products Regulations (R260 of 2015) under the Agricultural Products Standards Act (Act 119 of 1990).
* SANS 1674 (South African National Standard): Specifies microbiological and chemical quality requirements.
* SANS 10330: Relates to food safety management and hazard analysis (HACCP).

Compliance ensures product safety and alignment with international standards.

3. Technical Practice
South African dairy plants follow internationally recognised UHT conditions:
* Temperature: 135 - 150 ºC
* Holding Time: 2 - 5 seconds
* Cooling: Rapid cooling to < 20 ºC
* Packaging: Aseptic filling into sterile multilayer cartons or similar packaging.

These standards guarantee long shelf-life, consistent taste, and nutritional retention while meeting food safety regulations.

6. Quality and Nutritional Impact
UHT treatment causes minimal nutrient loss. Heat-sensitive vitamins (such as B1 and C) may reduce slightly, but proteins, fats, and carbohydrates remain largely unchanged. The process can result in a slightly 'cooked' flavour due to the Maillard reaction, but most consumers find UHT milk acceptable for daily use.

CONCLUSION
UHT milk processing is a scientifically advanced, globally standardised, and locally relevant technology that supports South Africa's dairy industry i achieving safety, stability, and accessibility goals.

Maintaining 135 - 150 ºC for 2 - 5 seconds in a closed aseptic system, followed by sterile packaging, ensures commercial sterility and a long shelf-life. These principles are directly applied within South African dairy operations, aligned with national and international quality standards.

UHT processing represents a perfect balance between food safety, product longevity, and consumer convenience, making it a critical component of modern dairy production in South Africa.